wikimedia/mediawiki-core

View on GitHub
includes/libs/rdbms/database/Database.php

Summary

Maintainability
F
1 mo
Test Coverage
<?php
/**
 * @defgroup Database Database
 *
 * This file deals with database interface functions
 * and query specifics/optimisations.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License along
 * with this program; if not, write to the Free Software Foundation, Inc.,
 * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
 * http://www.gnu.org/copyleft/gpl.html
 *
 * @file
 * @ingroup Database
 */
namespace Wikimedia\Rdbms;

use BagOStuff;
use Exception;
use HashBagOStuff;
use InvalidArgumentException;
use LogicException;
use MediaWiki\Installer\Services\InstallerDBSupport;
use Psr\Log\LoggerAwareInterface;
use Psr\Log\LoggerInterface;
use Psr\Log\NullLogger;
use RuntimeException;
use Throwable;
use UnexpectedValueException;
use Wikimedia\AtEase\AtEase;
use Wikimedia\ScopedCallback;
use Wikimedia\Timestamp\ConvertibleTimestamp;

/**
 * Relational database abstraction object
 *
 * @ingroup Database
 * @since 1.28
 */
abstract class Database implements IDatabase, IMaintainableDatabase, LoggerAwareInterface {
    /** @var BagOStuff APC cache */
    protected $srvCache;
    /** @var LoggerInterface */
    protected $connLogger;
    /** @var LoggerInterface */
    protected $queryLogger;
    /** @var LoggerInterface */
    protected $replLogger;
    /** @var callable Error logging callback */
    protected $errorLogger;
    /** @var callable Deprecation logging callback */
    protected $deprecationLogger;
    /** @var callable|null */
    protected $profiler;
    /** @var TransactionProfiler */
    protected $trxProfiler;

    /** @var DatabaseDomain */
    protected $currentDomain;

    /** @var object|resource|null Database connection */
    protected $conn;

    /** @var IDatabase|null Lazy handle to the master DB this server replicates from */
    private $lazyMasterHandle;

    /** @var string Server that this instance is currently connected to */
    protected $server;
    /** @var string User that this instance is currently connected under the name of */
    protected $user;
    /** @var string Password used to establish the current connection */
    protected $password;
    /** @var bool Whether this PHP instance is for a CLI script */
    protected $cliMode;
    /** @var string Agent name for query profiling */
    protected $agent;
    /** @var string Replication topology role of the server; one of the class ROLE_* constants */
    protected $topologyRole;
    /** @var string|null Host (or address) of the root master server for the replication topology */
    protected $topologyRootMaster;
    /** @var array Parameters used by initConnection() to establish a connection */
    protected $connectionParams;
    /** @var string[]|int[]|float[] SQL variables values to use for all new connections */
    protected $connectionVariables;
    /** @var int Row batch size to use for emulated INSERT SELECT queries */
    protected $nonNativeInsertSelectBatchSize;

    /** @var int Current bit field of class DBO_* constants */
    protected $flags;
    /** @var array Current LoadBalancer tracking information */
    protected $lbInfo = [];
    /** @var string Current SQL query delimiter */
    protected $delimiter = ';';
    /** @var array[] Current map of (table => (dbname, schema, prefix) map) */
    protected $tableAliases = [];
    /** @var string[] Current map of (index alias => index) */
    protected $indexAliases = [];
    /** @var array|null Current variables use for schema element placeholders */
    protected $schemaVars;

    /** @var string|bool|null Stashed value of html_errors INI setting */
    private $htmlErrors;
    /** @var int[] Prior flags member variable values */
    private $priorFlags = [];

    /** @var array Map of (name => 1) for locks obtained via lock() */
    protected $sessionNamedLocks = [];
    /** @var array Map of (table name => 1) for current TEMPORARY tables */
    protected $sessionTempTables = [];
    /** @var array Map of (table name => 1) for current TEMPORARY tables */
    protected $sessionDirtyTempTables = [];

    /** @var string ID of the active transaction or the empty string otherwise */
    private $trxShortId = '';
    /** @var int Transaction status */
    private $trxStatus = self::STATUS_TRX_NONE;
    /** @var Exception|null The last error that caused the status to become STATUS_TRX_ERROR */
    private $trxStatusCause;
    /** @var array|null Error details of the last statement-only rollback */
    private $trxStatusIgnoredCause;
    /** @var float|null UNIX timestamp at the time of BEGIN for the last transaction */
    private $trxTimestamp = null;
    /** @var float Replication lag estimate at the time of BEGIN for the last transaction */
    private $trxReplicaLag = null;
    /** @var string Name of the function that start the last transaction */
    private $trxFname = null;
    /** @var bool Whether possible write queries were done in the last transaction started */
    private $trxDoneWrites = false;
    /** @var bool Whether the current transaction was started implicitly due to DBO_TRX */
    private $trxAutomatic = false;
    /** @var int Counter for atomic savepoint identifiers (reset with each transaction) */
    private $trxAtomicCounter = 0;
    /** @var array List of (name, unique ID, savepoint ID) for each active atomic section level */
    private $trxAtomicLevels = [];
    /** @var bool Whether the current transaction was started implicitly by startAtomic() */
    private $trxAutomaticAtomic = false;
    /** @var string[] Write query callers of the current transaction */
    private $trxWriteCallers = [];
    /** @var float Seconds spent in write queries for the current transaction */
    private $trxWriteDuration = 0.0;
    /** @var int Number of write queries for the current transaction */
    private $trxWriteQueryCount = 0;
    /** @var int Number of rows affected by write queries for the current transaction */
    private $trxWriteAffectedRows = 0;
    /** @var float Like trxWriteQueryCount but excludes lock-bound, easy to replicate, queries */
    private $trxWriteAdjDuration = 0.0;
    /** @var int Number of write queries counted in trxWriteAdjDuration */
    private $trxWriteAdjQueryCount = 0;
    /** @var array[] List of (callable, method name, atomic section id) */
    private $trxIdleCallbacks = [];
    /** @var array[] List of (callable, method name, atomic section id) */
    private $trxPreCommitCallbacks = [];
    /**
     * @var array[] List of (callable, method name, atomic section id)
     * @phan-var array<array{0:callable,1:string,2:AtomicSectionIdentifier|null}>
     */
    private $trxEndCallbacks = [];
    /** @var array[] List of (callable, method name, atomic section id) */
    private $trxSectionCancelCallbacks = [];
    /** @var callable[] Map of (name => callable) */
    private $trxRecurringCallbacks = [];
    /** @var bool Whether to suppress triggering of transaction end callbacks */
    private $trxEndCallbacksSuppressed = false;

    /** @var integer|null Rows affected by the last query to query() or its CRUD wrappers */
    protected $affectedRowCount;

    /** @var float UNIX timestamp */
    private $lastPing = 0.0;
    /** @var string The last SQL query attempted */
    private $lastQuery = '';
    /** @var float|bool UNIX timestamp of last write query */
    private $lastWriteTime = false;
    /** @var string|bool */
    private $lastPhpError = false;
    /** @var float Query round trip time estimate */
    private $lastRoundTripEstimate = 0.0;

    /** @var int|null Integer ID of the managing LBFactory instance or null if none */
    private $ownerId;

    /** @var string Whether the database is a file on disk */
    public const ATTR_DB_IS_FILE = 'db-is-file';
    /** @var string Lock granularity is on the level of the entire database */
    public const ATTR_DB_LEVEL_LOCKING = 'db-level-locking';
    /** @var string The SCHEMA keyword refers to a grouping of tables in a database */
    public const ATTR_SCHEMAS_AS_TABLE_GROUPS = 'supports-schemas';

    /** @var int New Database instance will not be connected yet when returned */
    public const NEW_UNCONNECTED = 0;
    /** @var int New Database instance will already be connected when returned */
    public const NEW_CONNECTED = 1;

    /** @var int Transaction is in a error state requiring a full or savepoint rollback */
    public const STATUS_TRX_ERROR = 1;
    /** @var int Transaction is active and in a normal state */
    public const STATUS_TRX_OK = 2;
    /** @var int No transaction is active */
    public const STATUS_TRX_NONE = 3;

    /** @var string Idiom used when a cancelable atomic section started the transaction */
    private static $NOT_APPLICABLE = 'n/a';
    /** @var string Prefix to the atomic section counter used to make savepoint IDs */
    private static $SAVEPOINT_PREFIX = 'wikimedia_rdbms_atomic';

    /** @var int Writes to this temporary table do not affect lastDoneWrites() */
    private static $TEMP_NORMAL = 1;
    /** @var int Writes to this temporary table effect lastDoneWrites() */
    private static $TEMP_PSEUDO_PERMANENT = 2;

    /** @var int Number of times to re-try an operation in case of deadlock */
    private static $DEADLOCK_TRIES = 4;
    /** @var int Minimum time to wait before retry, in microseconds */
    private static $DEADLOCK_DELAY_MIN = 500000;
    /** @var int Maximum time to wait before retry */
    private static $DEADLOCK_DELAY_MAX = 1500000;

    /** @var int How long before it is worth doing a dummy query to test the connection */
    private static $PING_TTL = 1.0;
    /** @var string Dummy SQL query */
    private static $PING_QUERY = 'SELECT 1 AS ping';

    /** @var float Guess of how many seconds it takes to replicate a small insert */
    private static $TINY_WRITE_SEC = 0.010;
    /** @var float Consider a write slow if it took more than this many seconds */
    private static $SLOW_WRITE_SEC = 0.500;
    /** @var float Assume an insert of this many rows or less should be fast to replicate */
    private static $SMALL_WRITE_ROWS = 100;

    /** @var string[] List of DBO_* flags that can be changed after connection */
    protected static $MUTABLE_FLAGS = [
        'DBO_DEBUG',
        'DBO_NOBUFFER',
        'DBO_TRX',
        'DBO_DDLMODE',
    ];
    /** @var int Bit field of all DBO_* flags that can be changed after connection */
    protected static $DBO_MUTABLE = (
        self::DBO_DEBUG | self::DBO_NOBUFFER | self::DBO_TRX | self::DBO_DDLMODE
    );

    /**
     * @note exceptions for missing libraries/drivers should be thrown in initConnection()
     * @param array $params Parameters passed from Database::factory()
     */
    public function __construct( array $params ) {
        $this->connectionParams = [
            'host' => strlen( $params['host'] ) ? $params['host'] : null,
            'user' => strlen( $params['user'] ) ? $params['user'] : null,
            'dbname' => strlen( $params['dbname'] ) ? $params['dbname'] : null,
            'schema' => strlen( $params['schema'] ) ? $params['schema'] : null,
            'password' => is_string( $params['password'] ) ? $params['password'] : null,
            'tablePrefix' => (string)$params['tablePrefix']
        ];

        $this->lbInfo = $params['lbInfo'] ?? [];
        $this->lazyMasterHandle = $params['lazyMasterHandle'] ?? null;
        $this->connectionVariables = $params['variables'] ?? [];

        $this->flags = (int)$params['flags'];
        $this->cliMode = (bool)$params['cliMode'];
        $this->agent = (string)$params['agent'];
        $this->topologyRole = (string)$params['topologyRole'];
        $this->topologyRootMaster = (string)$params['topologicalMaster'];
        $this->nonNativeInsertSelectBatchSize = $params['nonNativeInsertSelectBatchSize'] ?? 10000;

        $this->srvCache = $params['srvCache'];
        $this->profiler = is_callable( $params['profiler'] ) ? $params['profiler'] : null;
        $this->trxProfiler = $params['trxProfiler'];
        $this->connLogger = $params['connLogger'];
        $this->queryLogger = $params['queryLogger'];
        $this->replLogger = $params['replLogger'];
        $this->errorLogger = $params['errorLogger'];
        $this->deprecationLogger = $params['deprecationLogger'];

        // Set initial dummy domain until open() sets the final DB/prefix
        $this->currentDomain = new DatabaseDomain(
            $params['dbname'] != '' ? $params['dbname'] : null,
            $params['schema'] != '' ? $params['schema'] : null,
            $params['tablePrefix']
        );

        $this->ownerId = $params['ownerId'] ?? null;
    }

    /**
     * Initialize the connection to the database over the wire (or to local files)
     *
     * @throws LogicException
     * @throws InvalidArgumentException
     * @throws DBConnectionError
     * @since 1.31
     */
    final public function initConnection() {
        if ( $this->isOpen() ) {
            throw new LogicException( __METHOD__ . ': already connected' );
        }
        // Establish the connection
        $this->doInitConnection();
    }

    /**
     * Actually connect to the database over the wire (or to local files)
     *
     * @throws DBConnectionError
     * @since 1.31
     */
    protected function doInitConnection() {
        $this->open(
            $this->connectionParams['host'],
            $this->connectionParams['user'],
            $this->connectionParams['password'],
            $this->connectionParams['dbname'],
            $this->connectionParams['schema'],
            $this->connectionParams['tablePrefix']
        );
    }

    /**
     * Open a new connection to the database (closing any existing one)
     *
     * @param string|null $server Database server host
     * @param string|null $user Database user name
     * @param string|null $password Database user password
     * @param string|null $dbName Database name
     * @param string|null $schema Database schema name
     * @param string $tablePrefix Table prefix
     * @throws DBConnectionError
     */
    abstract protected function open( $server, $user, $password, $dbName, $schema, $tablePrefix );

    /**
     * Construct a Database subclass instance given a database type and parameters
     *
     * This also connects to the database immediately upon object construction
     *
     * @param string $type A possible DB type (sqlite, mysql, postgres,...)
     * @param array $params Parameter map with keys:
     *   - host : The hostname of the DB server
     *   - user : The name of the database user the client operates under
     *   - password : The password for the database user
     *   - dbname : The name of the database to use where queries do not specify one.
     *      The database must exist or an error might be thrown. Setting this to the empty string
     *      will avoid any such errors and make the handle have no implicit database scope. This is
     *      useful for queries like SHOW STATUS, CREATE DATABASE, or DROP DATABASE. Note that a
     *      "database" in Postgres is rougly equivalent to an entire MySQL server. This the domain
     *      in which user names and such are defined, e.g. users are database-specific in Postgres.
     *   - schema : The database schema to use (if supported). A "schema" in Postgres is roughly
     *      equivalent to a "database" in MySQL. Note that MySQL and SQLite do not use schemas.
     *   - tablePrefix : Optional table prefix that is implicitly added on to all table names
     *      recognized in queries. This can be used in place of schemas for handle site farms.
     *   - flags : Optional bit field of DBO_* constants that define connection, protocol,
     *      buffering, and transaction behavior. It is STRONGLY adviced to leave the DBO_DEFAULT
     *      flag in place UNLESS this this database simply acts as a key/value store.
     *   - driver: Optional name of a specific DB client driver. For MySQL, there is only the
     *      'mysqli' driver; the old one 'mysql' has been removed.
     *   - variables: Optional map of session variables to set after connecting. This can be
     *      used to adjust lock timeouts or encoding modes and the like.
     *   - topologyRole: Optional IDatabase::ROLE_* constant for the server.
     *   - topologicalMaster: Optional name of the master server within the replication topology.
     *   - lbInfo: Optional map of field/values for the managing load balancer instance.
     *      The "master" and "replica" fields are used to flag the replication role of this
     *      database server and whether methods like getLag() should actually issue queries.
     *   - lazyMasterHandle: lazy-connecting IDatabase handle to the master DB for the cluster
     *      that this database belongs to. This is used for replication status purposes.
     *   - connLogger: Optional PSR-3 logger interface instance.
     *   - queryLogger: Optional PSR-3 logger interface instance.
     *   - profiler : Optional callback that takes a section name argument and returns
     *      a ScopedCallback instance that ends the profile section in its destructor.
     *      These will be called in query(), using a simplified version of the SQL that
     *      also includes the agent as a SQL comment.
     *   - trxProfiler: Optional TransactionProfiler instance.
     *   - errorLogger: Optional callback that takes an Exception and logs it.
     *   - deprecationLogger: Optional callback that takes a string and logs it.
     *   - cliMode: Whether to consider the execution context that of a CLI script.
     *   - agent: Optional name used to identify the end-user in query profiling/logging.
     *   - srvCache: Optional BagOStuff instance to an APC-style cache.
     *   - nonNativeInsertSelectBatchSize: Optional batch size for non-native INSERT SELECT.
     *   - ownerId: Optional integer ID of a LoadBalancer instance that manages this instance.
     * @param int $connect One of the class constants (NEW_CONNECTED, NEW_UNCONNECTED) [optional]
     * @return Database|null If the database driver or extension cannot be found
     * @throws InvalidArgumentException If the database driver or extension cannot be found
     * @since 1.18
     */
    final public static function factory( $type, $params = [], $connect = self::NEW_CONNECTED ) {
        $class = InstallerDBSupport::getInstance()->getDBDriverClass( $type );

        if ( class_exists( $class ) && is_subclass_of( $class, IDatabase::class ) ) {
            $params += [
                // Default configuration
                'host' => null,
                'user' => null,
                'password' => null,
                'dbname' => null,
                'schema' => null,
                'tablePrefix' => '',
                'flags' => 0,
                'variables' => [],
                'lbInfo' => [],
                'cliMode' => ( PHP_SAPI === 'cli' || PHP_SAPI === 'phpdbg' ),
                'agent' => '',
                'ownerId' => null,
                'topologyRole' => null,
                'topologicalMaster' => null,
                // Objects and callbacks
                'lazyMasterHandle' => $params['lazyMasterHandle'] ?? null,
                'srvCache' => $params['srvCache'] ?? new HashBagOStuff(),
                'profiler' => $params['profiler'] ?? null,
                'trxProfiler' => $params['trxProfiler'] ?? new TransactionProfiler(),
                'connLogger' => $params['connLogger'] ?? new NullLogger(),
                'queryLogger' => $params['queryLogger'] ?? new NullLogger(),
                'replLogger' => $params['replLogger'] ?? new NullLogger(),
                'errorLogger' => $params['errorLogger'] ?? function ( Throwable $e ) {
                    trigger_error( get_class( $e ) . ': ' . $e->getMessage(), E_USER_WARNING );
                },
                'deprecationLogger' => $params['deprecationLogger'] ?? function ( $msg ) {
                    trigger_error( $msg, E_USER_DEPRECATED );
                }
            ];

            /** @var Database $conn */
            $conn = new $class( $params );
            if ( $connect === self::NEW_CONNECTED ) {
                $conn->initConnection();
            }
        } else {
            $conn = null;
        }

        return $conn;
    }

    /**
     * @param string $dbType A possible DB type (sqlite, mysql, postgres,...)
     * @param string|null $driver Optional name of a specific DB client driver
     * @return array Map of (Database::ATTR_* constant => value) for all such constants
     * @throws InvalidArgumentException
     * @since 1.31
     */
    final public static function attributesFromType( $dbType, $driver = null ) {
        static $defaults = [
            self::ATTR_DB_IS_FILE => false,
            self::ATTR_DB_LEVEL_LOCKING => false,
            self::ATTR_SCHEMAS_AS_TABLE_GROUPS => false
        ];

        $class = InstallerDBSupport::getInstance()->getDBDriverClass( $dbType );

        return call_user_func( [ $class, 'getAttributes' ] ) + $defaults;
    }

    /**
     * @return array Map of (Database::ATTR_* constant => value)
     * @since 1.31
     */
    protected static function getAttributes() {
        return [];
    }

    /**
     * Set the PSR-3 logger interface to use for query logging. (The logger
     * interfaces for connection logging and error logging can be set with the
     * constructor.)
     *
     * @param LoggerInterface $logger
     */
    public function setLogger( LoggerInterface $logger ) {
        $this->queryLogger = $logger;
    }

    public function getServerInfo() {
        return $this->getServerVersion();
    }

    public function getTopologyRole() {
        return $this->topologyRole;
    }

    public function getTopologyRootMaster() {
        return $this->topologyRootMaster;
    }

    final public function trxLevel() {
        return ( $this->trxShortId != '' ) ? 1 : 0;
    }

    public function trxTimestamp() {
        return $this->trxLevel() ? $this->trxTimestamp : null;
    }

    /**
     * @return int One of the STATUS_TRX_* class constants
     * @since 1.31
     */
    public function trxStatus() {
        return $this->trxStatus;
    }

    public function tablePrefix( $prefix = null ) {
        $old = $this->currentDomain->getTablePrefix();
        if ( $prefix !== null ) {
            $this->currentDomain = new DatabaseDomain(
                $this->currentDomain->getDatabase(),
                $this->currentDomain->getSchema(),
                $prefix
            );
        }

        return $old;
    }

    public function dbSchema( $schema = null ) {
        if ( strlen( $schema ) && $this->getDBname() === null ) {
            throw new DBUnexpectedError( $this, "Cannot set schema to '$schema'; no database set" );
        }

        $old = $this->currentDomain->getSchema();
        if ( $schema !== null ) {
            $this->currentDomain = new DatabaseDomain(
                $this->currentDomain->getDatabase(),
                // DatabaseDomain uses null for unspecified schemas
                strlen( $schema ) ? $schema : null,
                $this->currentDomain->getTablePrefix()
            );
        }

        return (string)$old;
    }

    /**
     * @return string Schema to use to qualify relations in queries
     */
    protected function relationSchemaQualifier() {
        return $this->dbSchema();
    }

    public function getLBInfo( $name = null ) {
        if ( $name === null ) {
            return $this->lbInfo;
        }

        if ( array_key_exists( $name, $this->lbInfo ) ) {
            return $this->lbInfo[$name];
        }

        return null;
    }

    public function setLBInfo( $nameOrArray, $value = null ) {
        if ( is_array( $nameOrArray ) ) {
            $this->lbInfo = $nameOrArray;
        } elseif ( is_string( $nameOrArray ) ) {
            if ( $value !== null ) {
                $this->lbInfo[$nameOrArray] = $value;
            } else {
                unset( $this->lbInfo[$nameOrArray] );
            }
        } else {
            throw new InvalidArgumentException( "Got non-string key" );
        }
    }

    /**
     * Get a handle to the master server of the cluster to which this server belongs
     *
     * @return IDatabase|null
     * @since 1.27
     */
    protected function getLazyMasterHandle() {
        return $this->lazyMasterHandle;
    }

    public function implicitOrderby() {
        return true;
    }

    public function lastQuery() {
        return $this->lastQuery;
    }

    public function lastDoneWrites() {
        return $this->lastWriteTime ?: false;
    }

    public function writesPending() {
        return $this->trxLevel() && $this->trxDoneWrites;
    }

    public function writesOrCallbacksPending() {
        return $this->trxLevel() && (
            $this->trxDoneWrites ||
            $this->trxIdleCallbacks ||
            $this->trxPreCommitCallbacks ||
            $this->trxEndCallbacks ||
            $this->trxSectionCancelCallbacks
        );
    }

    public function preCommitCallbacksPending() {
        return $this->trxLevel() && $this->trxPreCommitCallbacks;
    }

    /**
     * @return string|null
     */
    final protected function getTransactionRoundId() {
        // If transaction round participation is enabled, see if one is active
        if ( $this->getFlag( self::DBO_TRX ) ) {
            $id = $this->getLBInfo( self::LB_TRX_ROUND_ID );

            return is_string( $id ) ? $id : null;
        }

        return null;
    }

    public function pendingWriteQueryDuration( $type = self::ESTIMATE_TOTAL ) {
        if ( !$this->trxLevel() ) {
            return false;
        } elseif ( !$this->trxDoneWrites ) {
            return 0.0;
        }

        switch ( $type ) {
            case self::ESTIMATE_DB_APPLY:
                return $this->pingAndCalculateLastTrxApplyTime();
            default: // everything
                return $this->trxWriteDuration;
        }
    }

    /**
     * @return float Time to apply writes to replicas based on trxWrite* fields
     */
    private function pingAndCalculateLastTrxApplyTime() {
        $this->ping( $rtt );

        $rttAdjTotal = $this->trxWriteAdjQueryCount * $rtt;
        $applyTime = max( $this->trxWriteAdjDuration - $rttAdjTotal, 0 );
        // For omitted queries, make them count as something at least
        $omitted = $this->trxWriteQueryCount - $this->trxWriteAdjQueryCount;
        $applyTime += self::$TINY_WRITE_SEC * $omitted;

        return $applyTime;
    }

    public function pendingWriteCallers() {
        return $this->trxLevel() ? $this->trxWriteCallers : [];
    }

    public function pendingWriteRowsAffected() {
        return $this->trxWriteAffectedRows;
    }

    /**
     * List the methods that have write queries or callbacks for the current transaction
     *
     * This method should not be used outside of Database/LoadBalancer
     *
     * @return string[]
     * @since 1.32
     */
    public function pendingWriteAndCallbackCallers() {
        $fnames = $this->pendingWriteCallers();
        foreach ( [
            $this->trxIdleCallbacks,
            $this->trxPreCommitCallbacks,
            $this->trxEndCallbacks,
            $this->trxSectionCancelCallbacks
        ] as $callbacks ) {
            foreach ( $callbacks as $callback ) {
                $fnames[] = $callback[1];
            }
        }

        return $fnames;
    }

    /**
     * @return string
     */
    private function flatAtomicSectionList() {
        return array_reduce( $this->trxAtomicLevels, function ( $accum, $v ) {
            return $accum === null ? $v[0] : "$accum, " . $v[0];
        } );
    }

    public function isOpen() {
        return (bool)$this->conn;
    }

    public function setFlag( $flag, $remember = self::REMEMBER_NOTHING ) {
        if ( $flag & ~static::$DBO_MUTABLE ) {
            throw new DBUnexpectedError(
                $this,
                "Got $flag (allowed: " . implode( ', ', static::$MUTABLE_FLAGS ) . ')'
            );
        }

        if ( $remember === self::REMEMBER_PRIOR ) {
            array_push( $this->priorFlags, $this->flags );
        }

        $this->flags |= $flag;
    }

    public function clearFlag( $flag, $remember = self::REMEMBER_NOTHING ) {
        if ( $flag & ~static::$DBO_MUTABLE ) {
            throw new DBUnexpectedError(
                $this,
                "Got $flag (allowed: " . implode( ', ', static::$MUTABLE_FLAGS ) . ')'
            );
        }

        if ( $remember === self::REMEMBER_PRIOR ) {
            array_push( $this->priorFlags, $this->flags );
        }

        $this->flags &= ~$flag;
    }

    public function restoreFlags( $state = self::RESTORE_PRIOR ) {
        if ( !$this->priorFlags ) {
            return;
        }

        if ( $state === self::RESTORE_INITIAL ) {
            $this->flags = reset( $this->priorFlags );
            $this->priorFlags = [];
        } else {
            $this->flags = array_pop( $this->priorFlags );
        }
    }

    public function getFlag( $flag ) {
        return ( ( $this->flags & $flag ) === $flag );
    }

    public function getDomainID() {
        return $this->currentDomain->getId();
    }

    /**
     * Get information about an index into an object
     * @param string $table Table name
     * @param string $index Index name
     * @param string $fname Calling function name
     * @return mixed Database-specific index description class or false if the index does not exist
     */
    abstract public function indexInfo( $table, $index, $fname = __METHOD__ );

    /**
     * Wrapper for addslashes()
     *
     * @param string $s String to be slashed.
     * @return string Slashed string.
     */
    abstract public function strencode( $s );

    /**
     * Set a custom error handler for logging errors during database connection
     */
    protected function installErrorHandler() {
        $this->lastPhpError = false;
        $this->htmlErrors = ini_set( 'html_errors', '0' );
        set_error_handler( [ $this, 'connectionErrorLogger' ] );
    }

    /**
     * Restore the previous error handler and return the last PHP error for this DB
     *
     * @return bool|string
     */
    protected function restoreErrorHandler() {
        restore_error_handler();
        if ( $this->htmlErrors !== false ) {
            ini_set( 'html_errors', $this->htmlErrors );
        }

        return $this->getLastPHPError();
    }

    /**
     * @return string|bool Last PHP error for this DB (typically connection errors)
     */
    protected function getLastPHPError() {
        if ( $this->lastPhpError ) {
            $error = preg_replace( '!\[<a.*</a>\]!', '', $this->lastPhpError );
            $error = preg_replace( '!^.*?:\s?(.*)$!', '$1', $error );

            return $error;
        }

        return false;
    }

    /**
     * Error handler for logging errors during database connection
     * This method should not be used outside of Database classes
     *
     * @param int $errno
     * @param string $errstr
     */
    public function connectionErrorLogger( $errno, $errstr ) {
        $this->lastPhpError = $errstr;
    }

    /**
     * Create a log context to pass to PSR-3 logger functions.
     *
     * @param array $extras Additional data to add to context
     * @return array
     */
    protected function getLogContext( array $extras = [] ) {
        return array_merge(
            [
                'db_server' => $this->server,
                'db_name' => $this->getDBname(),
                'db_user' => $this->user,
            ],
            $extras
        );
    }

    final public function close( $fname = __METHOD__, $owner = null ) {
        $error = null; // error to throw after disconnecting

        $wasOpen = (bool)$this->conn;
        // This should mostly do nothing if the connection is already closed
        if ( $this->conn ) {
            // Roll back any dangling transaction first
            if ( $this->trxLevel() ) {
                if ( $this->trxAtomicLevels ) {
                    // Cannot let incomplete atomic sections be committed
                    $levels = $this->flatAtomicSectionList();
                    $error = "$fname: atomic sections $levels are still open";
                } elseif ( $this->trxAutomatic ) {
                    // Only the connection manager can commit non-empty DBO_TRX transactions
                    // (empty ones we can silently roll back)
                    if ( $this->writesOrCallbacksPending() ) {
                        $error = "$fname: " .
                            "expected mass rollback of all peer transactions (DBO_TRX set)";
                    }
                } else {
                    // Manual transactions should have been committed or rolled
                    // back, even if empty.
                    $error = "$fname: transaction is still open (from {$this->trxFname})";
                }

                if ( $this->trxEndCallbacksSuppressed && $error === null ) {
                    $error = "$fname: callbacks are suppressed; cannot properly commit";
                }

                // Rollback the changes and run any callbacks as needed
                $this->rollback( __METHOD__, self::FLUSHING_INTERNAL );
            }

            // Close the actual connection in the binding handle
            $closed = $this->closeConnection();
        } else {
            $closed = true; // already closed; nothing to do
        }

        $this->conn = null;

        // Log or throw any unexpected errors after having disconnected
        if ( $error !== null ) {
            // T217819, T231443: if this is probably just LoadBalancer trying to recover from
            // errors and shutdown, then log any problems and move on since the request has to
            // end one way or another. Throwing errors is not very useful at some point.
            if ( $this->ownerId !== null && $owner === $this->ownerId ) {
                $this->queryLogger->error( $error );
            } else {
                throw new DBUnexpectedError( $this, $error );
            }
        }

        // Note that various subclasses call close() at the start of open(), which itself is
        // called by replaceLostConnection(). In that case, just because onTransactionResolution()
        // callbacks are pending does not mean that an exception should be thrown. Rather, they
        // will be executed after the reconnection step.
        if ( $wasOpen ) {
            // Sanity check that no callbacks are dangling
            $fnames = $this->pendingWriteAndCallbackCallers();
            if ( $fnames ) {
                throw new RuntimeException(
                    "Transaction callbacks are still pending: " . implode( ', ', $fnames )
                );
            }
        }

        return $closed;
    }

    /**
     * Make sure there is an open connection handle (alive or not) as a sanity check
     *
     * This guards against fatal errors to the binding handle not being defined
     * in cases where open() was never called or close() was already called
     *
     * @throws DBUnexpectedError
     */
    final protected function assertHasConnectionHandle() {
        if ( !$this->isOpen() ) {
            throw new DBUnexpectedError( $this, "DB connection was already closed" );
        }
    }

    /**
     * Make sure that this server is not marked as a replica nor read-only as a sanity check
     *
     * @throws DBReadOnlyError
     */
    protected function assertIsWritableMaster() {
        $info = $this->getReadOnlyReason();
        if ( $info ) {
            list( $reason, $source ) = $info;
            if ( $source === 'role' ) {
                throw new DBReadOnlyRoleError( $this, "Database is read-only: $reason" );
            } else {
                throw new DBReadOnlyError( $this, "Database is read-only: $reason" );
            }
        }
    }

    /**
     * Closes underlying database connection
     * @return bool Whether connection was closed successfully
     * @since 1.20
     */
    abstract protected function closeConnection();

    /**
     * Run a query and return a DBMS-dependent wrapper or boolean
     *
     * This is meant to handle the basic command of actually sending a query to the
     * server via the driver. No implicit transaction, reconnection, nor retry logic
     * should happen here. The higher level query() method is designed to handle those
     * sorts of concerns. This method should not trigger such higher level methods.
     *
     * The lastError() and lastErrno() methods should meaningfully reflect what error,
     * if any, occurred during the last call to this method. Methods like executeQuery(),
     * query(), select(), insert(), update(), delete(), and upsert() implement their calls
     * to doQuery() such that an immediately subsequent call to lastError()/lastErrno()
     * meaningfully reflects any error that occurred during that public query method call.
     *
     * For SELECT queries, this returns either:
     *   - a) A driver-specific value/resource, only on success. This can be iterated
     *        over by calling fetchObject()/fetchRow() until there are no more rows.
     *        Alternatively, the result can be passed to resultObject() to obtain an
     *        IResultWrapper instance which can then be iterated over via "foreach".
     *   - b) False, on any query failure
     *
     * For non-SELECT queries, this returns either:
     *   - a) A driver-specific value/resource, only on success
     *   - b) True, only on success (e.g. no meaningful result other than "OK")
     *   - c) False, on any query failure
     *
     * @param string $sql SQL query
     * @return mixed|bool An object, resource, or true on success; false on failure
     */
    abstract protected function doQuery( $sql );

    /**
     * Determine whether a query writes to the DB. When in doubt, this returns true.
     *
     * Main use cases:
     *
     * - Subsequent web requests should not need to wait for replication from
     *   the master position seen by this web request, unless this request made
     *   changes to the master. This is handled by ChronologyProtector by checking
     *   doneWrites() at the end of the request. doneWrites() returns true if any
     *   query set lastWriteTime; which query() does based on isWriteQuery().
     *
     * - Reject write queries to replica DBs, in query().
     *
     * @param string $sql
     * @param int $flags Query flags to query()
     * @return bool
     */
    protected function isWriteQuery( $sql, $flags ) {
        if (
            $this->fieldHasBit( $flags, self::QUERY_CHANGE_ROWS ) ||
            $this->fieldHasBit( $flags, self::QUERY_CHANGE_SCHEMA )
        ) {
            return true;
        } elseif ( $this->fieldHasBit( $flags, self::QUERY_CHANGE_NONE ) ) {
            return false;
        }
        // BEGIN and COMMIT queries are considered read queries here.
        // Database backends and drivers (MySQL, MariaDB, php-mysqli) generally
        // treat these as write queries, in that their results have "affected rows"
        // as meta data as from writes, instead of "num rows" as from reads.
        // But, we treat them as read queries because when reading data (from
        // either replica or master) we use transactions to enable repeatable-read
        // snapshots, which ensures we get consistent results from the same snapshot
        // for all queries within a request. Use cases:
        // - Treating these as writes would trigger ChronologyProtector (see method doc).
        // - We use this method to reject writes to replicas, but we need to allow
        //   use of transactions on replicas for read snapshots. This is fine given
        //   that transactions by themselves don't make changes, only actual writes
        //   within the transaction matter, which we still detect.
        return !preg_match(
            '/^\s*(?:SELECT|BEGIN|ROLLBACK|COMMIT|SAVEPOINT|RELEASE|SET|SHOW|EXPLAIN|USE|\(SELECT)\b/i',
            $sql
        );
    }

    /**
     * @param string $sql
     * @return string|null
     */
    protected function getQueryVerb( $sql ) {
        return preg_match( '/^\s*([a-z]+)/i', $sql, $m ) ? strtoupper( $m[1] ) : null;
    }

    /**
     * Determine whether a SQL statement is sensitive to isolation level.
     *
     * A SQL statement is considered transactable if its result could vary
     * depending on the transaction isolation level. Operational commands
     * such as 'SET' and 'SHOW' are not considered to be transactable.
     *
     * Main purpose: Used by query() to decide whether to begin a transaction
     * before the current query (in DBO_TRX mode, on by default).
     *
     * @param string $sql
     * @return bool
     */
    protected function isTransactableQuery( $sql ) {
        return !in_array(
            $this->getQueryVerb( $sql ),
            [ 'BEGIN', 'ROLLBACK', 'COMMIT', 'SET', 'SHOW', 'CREATE', 'ALTER', 'USE', 'SHOW' ],
            true
        );
    }

    /**
     * @param string $sql SQL query
     * @param bool $pseudoPermanent Treat any table from CREATE TEMPORARY as pseudo-permanent
     * @return array[] List of change n-tuples with:
     *   - int: self::TEMP_* constant for temp table operations
     *   - string: SQL query verb from $sql
     *   - string: Name of the temp table changed in $sql
     */
    protected function getTempTableWrites( $sql, $pseudoPermanent ) {
        // Regexes for basic queries that can create/change/drop temporary tables.
        // For simplicity, this only looks for tables with sane, alphanumeric, names;
        // temporary tables only need simple programming names anyway.
        static $regexes = null;
        if ( $regexes === null ) {
            // Regex with a group for quoted table 0 and a group for quoted tables 1..N
            $qts = '(\w+|`\w+`|\'\w+\'|"\w+")(?:\s*,\s*(\w+|`\w+`|\'\w+\'|"\w+"))*';
            // Regex to get query verb, table 0, and tables 1..N
            $regexes = [
                // DML write queries
                "/^(INSERT|REPLACE)\s+(?:\w+\s+)*?INTO\s+$qts/i",
                "/^(UPDATE)(?:\s+OR\s+\w+|\s+IGNORE|\s+ONLY)?\s+$qts/i",
                "/^(DELETE)\s+(?:\w+\s+)*?FROM(?:\s+ONLY)?\s+$qts/i",
                // DDL write queries
                "/^(CREATE)\s+TEMPORARY\s+TABLE(?:\s+IF\s+NOT\s+EXISTS)?\s+$qts/i",
                "/^(DROP)\s+(?:TEMPORARY\s+)?TABLE(?:\s+IF\s+EXISTS)?\s+$qts/i",
                "/^(TRUNCATE)\s+(?:TEMPORARY\s+)?TABLE\s+$qts/i",
                "/^(ALTER)\s+TABLE\s+$qts/i"
            ];
        }

        $queryVerb = null;
        $queryTables = [];
        foreach ( $regexes as $regex ) {
            if ( preg_match( $regex, $sql, $m, PREG_UNMATCHED_AS_NULL ) ) {
                $queryVerb = $m[1];
                $queryTables[] = trim( $m[2], "\"'`" );
                foreach ( ( $m[3] ?? [] ) as $quotedTable ) {
                    $queryTables[] = trim( $quotedTable, "\"'`" );
                }
                break;
            }
        }

        $tempTableChanges = [];
        foreach ( $queryTables as $table ) {
            if ( $queryVerb === 'CREATE' ) {
                // Record the type of temporary table being created
                $tableType = $pseudoPermanent ? self::$TEMP_PSEUDO_PERMANENT : self::$TEMP_NORMAL;
            } else {
                $tableType = $this->sessionTempTables[$table] ?? null;
            }

            if ( $tableType !== null ) {
                $tempTableChanges[] = [ $tableType, $queryVerb, $table ];
            }
        }

        return $tempTableChanges;
    }

    /**
     * @param IResultWrapper|bool $ret
     * @param array[] $changes List of change n-tuples with from getTempWrites()
     */
    protected function registerTempWrites( $ret, array $changes ) {
        if ( $ret === false ) {
            return;
        }

        foreach ( $changes as list( $tmpTableType, $verb, $table ) ) {
            switch ( $verb ) {
                case 'CREATE':
                    $this->sessionTempTables[$table] = $tmpTableType;
                    break;
                case 'DROP':
                    unset( $this->sessionTempTables[$table] );
                    unset( $this->sessionDirtyTempTables[$table] );
                    break;
                case 'TRUNCATE':
                    unset( $this->sessionDirtyTempTables[$table] );
                    break;
                default:
                    $this->sessionDirtyTempTables[$table] = 1;
                    break;
            }
        }
    }

    /**
     * Check if the table is both a TEMPORARY table and has not yet received CRUD operations
     *
     * @param string $table
     * @return bool
     * @since 1.35
     */
    protected function isPristineTemporaryTable( $table ) {
        $rawTable = $this->tableName( $table, 'raw' );

        return (
            isset( $this->sessionTempTables[$rawTable] ) &&
            !isset( $this->sessionDirtyTempTables[$rawTable] )
        );
    }

    public function query( $sql, $fname = __METHOD__, $flags = self::QUERY_NORMAL ) {
        $flags = (int)$flags; // b/c; this field used to be a bool
        // Sanity check that the SQL query is appropriate in the current context and is
        // allowed for an outside caller (e.g. does not break transaction/session tracking).
        $this->assertQueryIsCurrentlyAllowed( $sql, $fname );

        // Send the query to the server and fetch any corresponding errors
        list( $ret, $err, $errno, $unignorable ) = $this->executeQuery( $sql, $fname, $flags );
        if ( $ret === false ) {
            $ignoreErrors = $this->fieldHasBit( $flags, self::QUERY_SILENCE_ERRORS );
            // Throw an error unless both the ignore flag was set and a rollback is not needed
            $this->reportQueryError( $err, $errno, $sql, $fname, $ignoreErrors && !$unignorable );
        }

        return $this->resultObject( $ret );
    }

    /**
     * Execute a query, retrying it if there is a recoverable connection loss
     *
     * This is similar to query() except:
     *   - It does not prevent all non-ROLLBACK queries if there is a corrupted transaction
     *   - It does not disallow raw queries that are supposed to use dedicated IDatabase methods
     *   - It does not throw exceptions for common error cases
     *
     * This is meant for internal use with Database subclasses.
     *
     * @param string $sql Original SQL query
     * @param string $fname Name of the calling function
     * @param int $flags Bit field of class QUERY_* constants
     * @return array An n-tuple of:
     *   - mixed|bool: An object, resource, or true on success; false on failure
     *   - string: The result of calling lastError()
     *   - int: The result of calling lastErrno()
     *   - bool: Whether a rollback is needed to allow future non-rollback queries
     * @throws DBUnexpectedError
     */
    final protected function executeQuery( $sql, $fname, $flags ) {
        $this->assertHasConnectionHandle();

        $priorTransaction = $this->trxLevel();

        if ( $this->isWriteQuery( $sql, $flags ) ) {
            // In theory, non-persistent writes are allowed in read-only mode, but due to things
            // like https://bugs.mysql.com/bug.php?id=33669 that might not work anyway...
            $this->assertIsWritableMaster();
            // Do not treat temporary table writes as "meaningful writes" since they are only
            // visible to one session and are not permanent. Profile them as reads. Integration
            // tests can override this behavior via $flags.
            $pseudoPermanent = $this->fieldHasBit( $flags, self::QUERY_PSEUDO_PERMANENT );
            $tempTableChanges = $this->getTempTableWrites( $sql, $pseudoPermanent );
            $isPermWrite = !$tempTableChanges;
            foreach ( $tempTableChanges as list( $tmpType ) ) {
                $isPermWrite = $isPermWrite || ( $tmpType !== self::$TEMP_NORMAL );
            }
            // DBConnRef uses QUERY_REPLICA_ROLE to enforce the replica role for raw SQL queries
            if ( $isPermWrite && $this->fieldHasBit( $flags, self::QUERY_REPLICA_ROLE ) ) {
                throw new DBReadOnlyRoleError( $this, "Cannot write; target role is DB_REPLICA" );
            }
        } else {
            // No permanent writes in this query
            $isPermWrite = false;
            // No temporary tables written to either
            $tempTableChanges = [];
        }

        // Add trace comment to the begin of the sql string, right after the operator.
        // Or, for one-word queries (like "BEGIN" or COMMIT") add it to the end (T44598).
        $encAgent = str_replace( '/', '-', $this->agent );
        $commentedSql = preg_replace( '/\s|$/', " /* $fname $encAgent */ ", $sql, 1 );

        // Send the query to the server and fetch any corresponding errors.
        // This also doubles as a "ping" to see if the connection was dropped.
        list( $ret, $err, $errno, $recoverableSR, $recoverableCL, $reconnected ) =
            $this->executeQueryAttempt( $sql, $commentedSql, $isPermWrite, $fname, $flags );

        // Check if the query failed due to a recoverable connection loss
        $allowRetry = !$this->fieldHasBit( $flags, self::QUERY_NO_RETRY );
        if ( $ret === false && $recoverableCL && $reconnected && $allowRetry ) {
            // Silently resend the query to the server since it is safe and possible
            list( $ret, $err, $errno, $recoverableSR, $recoverableCL ) =
                $this->executeQueryAttempt( $sql, $commentedSql, $isPermWrite, $fname, $flags );
        }

        // Register creation and dropping of temporary tables
        $this->registerTempWrites( $ret, $tempTableChanges );

        $corruptedTrx = false;

        if ( $ret === false ) {
            if ( $priorTransaction ) {
                if ( $recoverableSR ) {
                    # We're ignoring an error that caused just the current query to be aborted.
                    # But log the cause so we can log a deprecation notice if a caller actually
                    # does ignore it.
                    $this->trxStatusIgnoredCause = [ $err, $errno, $fname ];
                } elseif ( !$recoverableCL ) {
                    # Either the query was aborted or all queries after BEGIN where aborted.
                    # In the first case, the only options going forward are (a) ROLLBACK, or
                    # (b) ROLLBACK TO SAVEPOINT (if one was set). If the later case, the only
                    # option is ROLLBACK, since the snapshots would have been released.
                    $corruptedTrx = true; // cannot recover
                    $this->trxStatus = self::STATUS_TRX_ERROR;
                    $this->trxStatusCause = $this->getQueryException( $err, $errno, $sql, $fname );
                    $this->trxStatusIgnoredCause = null;
                }
            }
        }

        return [ $ret, $err, $errno, $corruptedTrx ];
    }

    /**
     * Wrapper for doQuery() that handles DBO_TRX, profiling, logging, affected row count
     * tracking, and reconnects (without retry) on query failure due to connection loss
     *
     * @param string $sql Original SQL query
     * @param string $commentedSql SQL query with debugging/trace comment
     * @param bool $isPermWrite Whether the query is a (non-temporary table) write
     * @param string $fname Name of the calling function
     * @param int $flags Bit field of class QUERY_* constants
     * @return array An n-tuple of:
     *   - mixed|bool: An object, resource, or true on success; false on failure
     *   - string: The result of calling lastError()
     *   - int: The result of calling lastErrno()
     *      - bool: Whether a statement rollback error occurred
     *   - bool: Whether a disconnect *both* happened *and* was recoverable
     *   - bool: Whether a reconnection attempt was *both* made *and* succeeded
     * @throws DBUnexpectedError
     */
    private function executeQueryAttempt( $sql, $commentedSql, $isPermWrite, $fname, $flags ) {
        $priorWritesPending = $this->writesOrCallbacksPending();

        if ( ( $flags & self::QUERY_IGNORE_DBO_TRX ) == 0 ) {
            $this->beginIfImplied( $sql, $fname );
        }

        // Keep track of whether the transaction has write queries pending
        if ( $isPermWrite ) {
            $this->lastWriteTime = microtime( true );
            if ( $this->trxLevel() && !$this->trxDoneWrites ) {
                $this->trxDoneWrites = true;
                $this->trxProfiler->transactionWritingIn(
                    $this->server, $this->getDomainID(), $this->trxShortId );
            }
        }

        $prefix = $this->topologyRole ? 'query-m: ' : 'query: ';
        $generalizedSql = new GeneralizedSql( $sql, $this->trxShortId, $prefix );

        $startTime = microtime( true );
        $ps = $this->profiler
            ? ( $this->profiler )( $generalizedSql->stringify() )
            : null;
        $this->affectedRowCount = null;
        $this->lastQuery = $sql;
        $ret = $this->doQuery( $commentedSql );
        $lastError = $this->lastError();
        $lastErrno = $this->lastErrno();

        $this->affectedRowCount = $this->affectedRows();
        unset( $ps ); // profile out (if set)
        $queryRuntime = max( microtime( true ) - $startTime, 0.0 );

        $recoverableSR = false; // recoverable statement rollback?
        $recoverableCL = false; // recoverable connection loss?
        $reconnected = false; // reconnection both attempted and succeeded?

        if ( $ret !== false ) {
            $this->lastPing = $startTime;
            if ( $isPermWrite && $this->trxLevel() ) {
                $this->updateTrxWriteQueryTime( $sql, $queryRuntime, $this->affectedRows() );
                $this->trxWriteCallers[] = $fname;
            }
        } elseif ( $this->wasConnectionError( $lastErrno ) ) {
            # Check if no meaningful session state was lost
            $recoverableCL = $this->canRecoverFromDisconnect( $sql, $priorWritesPending );
            # Update session state tracking and try to restore the connection
            $reconnected = $this->replaceLostConnection( __METHOD__ );
        } else {
            # Check if only the last query was rolled back
            $recoverableSR = $this->wasKnownStatementRollbackError();
        }

        if ( $sql === self::$PING_QUERY ) {
            $this->lastRoundTripEstimate = $queryRuntime;
        }

        $this->trxProfiler->recordQueryCompletion(
            $generalizedSql,
            $startTime,
            $isPermWrite,
            $isPermWrite ? $this->affectedRows() : $this->numRows( $ret )
        );

        // Avoid the overhead of logging calls unless debug mode is enabled
        if ( $this->getFlag( self::DBO_DEBUG ) ) {
            $this->queryLogger->debug(
                "{method} [{runtime}s] {db_host}: {sql}",
                [
                    'method' => $fname,
                    'db_host' => $this->getServer(),
                    'sql' => $sql,
                    'domain' => $this->getDomainID(),
                    'runtime' => round( $queryRuntime, 3 )
                ]
            );
        }

        return [ $ret, $lastError, $lastErrno, $recoverableSR, $recoverableCL, $reconnected ];
    }

    /**
     * Start an implicit transaction if DBO_TRX is enabled and no transaction is active
     *
     * @param string $sql
     * @param string $fname
     */
    private function beginIfImplied( $sql, $fname ) {
        if (
            !$this->trxLevel() &&
            $this->getFlag( self::DBO_TRX ) &&
            $this->isTransactableQuery( $sql )
        ) {
            $this->begin( __METHOD__ . " ($fname)", self::TRANSACTION_INTERNAL );
            $this->trxAutomatic = true;
        }
    }

    /**
     * Update the estimated run-time of a query, not counting large row lock times
     *
     * LoadBalancer can be set to rollback transactions that will create huge replication
     * lag. It bases this estimate off of pendingWriteQueryDuration(). Certain simple
     * queries, like inserting a row can take a long time due to row locking. This method
     * uses some simple heuristics to discount those cases.
     *
     * @param string $sql A SQL write query
     * @param float $runtime Total runtime, including RTT
     * @param int $affected Affected row count
     */
    private function updateTrxWriteQueryTime( $sql, $runtime, $affected ) {
        // Whether this is indicative of replica DB runtime (except for RBR or ws_repl)
        $indicativeOfReplicaRuntime = true;
        if ( $runtime > self::$SLOW_WRITE_SEC ) {
            $verb = $this->getQueryVerb( $sql );
            // insert(), upsert(), replace() are fast unless bulky in size or blocked on locks
            if ( $verb === 'INSERT' ) {
                $indicativeOfReplicaRuntime = $this->affectedRows() > self::$SMALL_WRITE_ROWS;
            } elseif ( $verb === 'REPLACE' ) {
                $indicativeOfReplicaRuntime = $this->affectedRows() > self::$SMALL_WRITE_ROWS / 2;
            }
        }

        $this->trxWriteDuration += $runtime;
        $this->trxWriteQueryCount += 1;
        $this->trxWriteAffectedRows += $affected;
        if ( $indicativeOfReplicaRuntime ) {
            $this->trxWriteAdjDuration += $runtime;
            $this->trxWriteAdjQueryCount += 1;
        }
    }

    /**
     * Error out if the DB is not in a valid state for a query via query()
     *
     * @param string $sql
     * @param string $fname
     * @throws DBTransactionStateError
     */
    private function assertQueryIsCurrentlyAllowed( $sql, $fname ) {
        $verb = $this->getQueryVerb( $sql );
        if ( $verb === 'USE' ) {
            throw new DBUnexpectedError( $this, "Got USE query; use selectDomain() instead" );
        }

        if ( $verb === 'ROLLBACK' ) { // transaction/savepoint
            return;
        }

        if ( $this->trxStatus < self::STATUS_TRX_OK ) {
            throw new DBTransactionStateError(
                $this,
                "Cannot execute query from $fname while transaction status is ERROR",
                [],
                $this->trxStatusCause
            );
        } elseif ( $this->trxStatus === self::STATUS_TRX_OK && $this->trxStatusIgnoredCause ) {
            list( $iLastError, $iLastErrno, $iFname ) = $this->trxStatusIgnoredCause;
            call_user_func( $this->deprecationLogger,
                "Caller from $fname ignored an error originally raised from $iFname: " .
                "[$iLastErrno] $iLastError"
            );
            $this->trxStatusIgnoredCause = null;
        }
    }

    public function assertNoOpenTransactions() {
        if ( $this->explicitTrxActive() ) {
            throw new DBTransactionError(
                $this,
                "Explicit transaction still active. A caller may have caught an error. "
                . "Open transactions: " . $this->flatAtomicSectionList()
            );
        }
    }

    /**
     * Determine whether it is safe to retry queries after a database connection is lost
     *
     * @param string $sql SQL query
     * @param bool $priorWritesPending Whether there is a transaction open with
     *     possible write queries or transaction pre-commit/idle callbacks
     *     waiting on it to finish.
     * @return bool True if it is safe to retry the query, false otherwise
     */
    private function canRecoverFromDisconnect( $sql, $priorWritesPending ) {
        # Transaction dropped; this can mean lost writes, or REPEATABLE-READ snapshots.
        # Dropped connections also mean that named locks are automatically released.
        # Only allow error suppression in autocommit mode or when the lost transaction
        # didn't matter anyway (aside from DBO_TRX snapshot loss).
        if ( $this->sessionNamedLocks ) {
            return false; // possible critical section violation
        } elseif ( $this->sessionTempTables ) {
            return false; // tables might be queried latter
        } elseif ( $sql === 'COMMIT' ) {
            return !$priorWritesPending; // nothing written anyway? (T127428)
        } elseif ( $sql === 'ROLLBACK' ) {
            return true; // transaction lost...which is also what was requested :)
        } elseif ( $this->explicitTrxActive() ) {
            return false; // don't drop atomicity and explicit snapshots
        } elseif ( $priorWritesPending ) {
            return false; // prior writes lost from implicit transaction
        }

        return true;
    }

    /**
     * Clean things up after session (and thus transaction) loss before reconnect
     */
    private function handleSessionLossPreconnect() {
        // Clean up tracking of session-level things...
        // https://dev.mysql.com/doc/refman/5.7/en/implicit-commit.html
        // https://www.postgresql.org/docs/9.2/static/sql-createtable.html (ignoring ON COMMIT)
        $this->sessionTempTables = [];
        $this->sessionDirtyTempTables = [];
        // https://dev.mysql.com/doc/refman/5.7/en/miscellaneous-functions.html#function_get-lock
        // https://www.postgresql.org/docs/9.4/static/functions-admin.html#FUNCTIONS-ADVISORY-LOCKS
        $this->sessionNamedLocks = [];
        // Session loss implies transaction loss
        $oldTrxShortId = $this->consumeTrxShortId();
        $this->trxAtomicCounter = 0;
        $this->trxIdleCallbacks = []; // T67263; transaction already lost
        $this->trxPreCommitCallbacks = []; // T67263; transaction already lost
        // Clear additional subclass fields
        $this->doHandleSessionLossPreconnect();
        // @note: leave trxRecurringCallbacks in place
        if ( $this->trxDoneWrites ) {
            $this->trxProfiler->transactionWritingOut(
                $this->server,
                $this->getDomainID(),
                $oldTrxShortId,
                $this->pendingWriteQueryDuration( self::ESTIMATE_TOTAL ),
                $this->trxWriteAffectedRows
            );
        }
    }

    /**
     * Reset any additional subclass trx* and session* fields
     */
    protected function doHandleSessionLossPreconnect() {
        // no-op
    }

    /**
     * Clean things up after session (and thus transaction) loss after reconnect
     */
    private function handleSessionLossPostconnect() {
        try {
            // Handle callbacks in trxEndCallbacks, e.g. onTransactionResolution().
            // If callback suppression is set then the array will remain unhandled.
            $this->runOnTransactionIdleCallbacks( self::TRIGGER_ROLLBACK );
        } catch ( Throwable $ex ) {
            // Already logged; move on...
        }
        try {
            // Handle callbacks in trxRecurringCallbacks, e.g. setTransactionListener()
            $this->runTransactionListenerCallbacks( self::TRIGGER_ROLLBACK );
        } catch ( Throwable $ex ) {
            // Already logged; move on...
        }
    }

    /**
     * Reset the transaction ID and return the old one
     *
     * @return string The old transaction ID or the empty string if there wasn't one
     */
    private function consumeTrxShortId() {
        $old = $this->trxShortId;
        $this->trxShortId = '';

        return $old;
    }

    /**
     * Checks whether the cause of the error is detected to be a timeout.
     *
     * It returns false by default, and not all engines support detecting this yet.
     * If this returns false, it will be treated as a generic query error.
     *
     * @param string $error Error text
     * @param int $errno Error number
     * @return bool
     */
    protected function wasQueryTimeout( $error, $errno ) {
        return false;
    }

    /**
     * Report a query error. Log the error, and if neither the object ignore
     * flag nor the $ignoreErrors flag is set, throw a DBQueryError.
     *
     * @param string $error
     * @param int $errno
     * @param string $sql
     * @param string $fname
     * @param bool $ignore
     * @throws DBQueryError
     */
    public function reportQueryError( $error, $errno, $sql, $fname, $ignore = false ) {
        if ( $ignore ) {
            $this->queryLogger->debug( "SQL ERROR (ignored): $error" );
        } else {
            throw $this->getQueryExceptionAndLog( $error, $errno, $sql, $fname );
        }
    }

    /**
     * @param string $error
     * @param string|int $errno
     * @param string $sql
     * @param string $fname
     * @return DBError
     */
    private function getQueryExceptionAndLog( $error, $errno, $sql, $fname ) {
        // Information that instances of the same problem have in common should
        // not be normalized (T255202).
        $this->queryLogger->error(
            "Error $errno from $fname, {error} {sql1line} {db_server}",
            $this->getLogContext( [
                'method' => __METHOD__,
                'errno' => $errno,
                'error' => $error,
                'sql1line' => mb_substr( str_replace( "\n", "\\n", $sql ), 0, 5 * 1024 ),
                'fname' => $fname,
                'exception' => new RuntimeException()
            ] )
        );
        return $this->getQueryException( $error, $errno, $sql, $fname );
    }

    /**
     * @param string $error
     * @param string|int $errno
     * @param string $sql
     * @param string $fname
     * @return DBError
     */
    private function getQueryException( $error, $errno, $sql, $fname ) {
        if ( $this->wasQueryTimeout( $error, $errno ) ) {
            return new DBQueryTimeoutError( $this, $error, $errno, $sql, $fname );
        } elseif ( $this->wasConnectionError( $errno ) ) {
            return new DBQueryDisconnectedError( $this, $error, $errno, $sql, $fname );
        } else {
            return new DBQueryError( $this, $error, $errno, $sql, $fname );
        }
    }

    /**
     * @param string $error
     * @return DBConnectionError
     */
    final protected function newExceptionAfterConnectError( $error ) {
        // Connection was not fully initialized and is not safe for use
        $this->conn = null;

        $this->connLogger->error(
            "Error connecting to {db_server} as user {db_user}: {error}",
            $this->getLogContext( [
                'error' => $error,
                'exception' => new RuntimeException()
            ] )
        );

        return new DBConnectionError( $this, $error );
    }

    public function freeResult( $res ) {
    }

    public function newSelectQueryBuilder() {
        return new SelectQueryBuilder( $this );
    }

    public function selectField(
        $table, $var, $cond = '', $fname = __METHOD__, $options = [], $join_conds = []
    ) {
        if ( $var === '*' ) { // sanity
            throw new DBUnexpectedError( $this, "Cannot use a * field: got '$var'" );
        }

        $options = $this->normalizeOptions( $options );
        $options['LIMIT'] = 1;

        $res = $this->select( $table, $var, $cond, $fname, $options, $join_conds );
        if ( $res === false ) {
            throw new DBUnexpectedError( $this, "Got false from select()" );
        }

        $row = $this->fetchRow( $res );
        if ( $row === false ) {
            return false;
        }

        return reset( $row );
    }

    public function selectFieldValues(
        $table, $var, $cond = '', $fname = __METHOD__, $options = [], $join_conds = []
    ) {
        if ( $var === '*' ) { // sanity
            throw new DBUnexpectedError( $this, "Cannot use a * field" );
        } elseif ( !is_string( $var ) ) { // sanity
            throw new DBUnexpectedError( $this, "Cannot use an array of fields" );
        }

        $options = $this->normalizeOptions( $options );
        $res = $this->select( $table, [ 'value' => $var ], $cond, $fname, $options, $join_conds );
        if ( $res === false ) {
            throw new DBUnexpectedError( $this, "Got false from select()" );
        }

        $values = [];
        foreach ( $res as $row ) {
            $values[] = $row->value;
        }

        return $values;
    }

    /**
     * Returns an optional USE INDEX clause to go after the table, and a
     * string to go at the end of the query.
     *
     * @see Database::select()
     *
     * @param array $options Associative array of options to be turned into
     *   an SQL query, valid keys are listed in the function.
     * @return array
     */
    protected function makeSelectOptions( array $options ) {
        $preLimitTail = $postLimitTail = '';
        $startOpts = '';

        $noKeyOptions = [];

        foreach ( $options as $key => $option ) {
            if ( is_numeric( $key ) ) {
                $noKeyOptions[$option] = true;
            }
        }

        $preLimitTail .= $this->makeGroupByWithHaving( $options );

        $preLimitTail .= $this->makeOrderBy( $options );

        if ( isset( $noKeyOptions['FOR UPDATE'] ) ) {
            $postLimitTail .= ' FOR UPDATE';
        }

        if ( isset( $noKeyOptions['LOCK IN SHARE MODE'] ) ) {
            $postLimitTail .= ' LOCK IN SHARE MODE';
        }

        if ( isset( $noKeyOptions['DISTINCT'] ) || isset( $noKeyOptions['DISTINCTROW'] ) ) {
            $startOpts .= 'DISTINCT';
        }

        # Various MySQL extensions
        if ( isset( $noKeyOptions['STRAIGHT_JOIN'] ) ) {
            $startOpts .= ' /*! STRAIGHT_JOIN */';
        }

        if ( isset( $noKeyOptions['SQL_BIG_RESULT'] ) ) {
            $startOpts .= ' SQL_BIG_RESULT';
        }

        if ( isset( $noKeyOptions['SQL_BUFFER_RESULT'] ) ) {
            $startOpts .= ' SQL_BUFFER_RESULT';
        }

        if ( isset( $noKeyOptions['SQL_SMALL_RESULT'] ) ) {
            $startOpts .= ' SQL_SMALL_RESULT';
        }

        if ( isset( $noKeyOptions['SQL_CALC_FOUND_ROWS'] ) ) {
            $startOpts .= ' SQL_CALC_FOUND_ROWS';
        }

        if ( isset( $options['USE INDEX'] ) && is_string( $options['USE INDEX'] ) ) {
            $useIndex = $this->useIndexClause( $options['USE INDEX'] );
        } else {
            $useIndex = '';
        }
        if ( isset( $options['IGNORE INDEX'] ) && is_string( $options['IGNORE INDEX'] ) ) {
            $ignoreIndex = $this->ignoreIndexClause( $options['IGNORE INDEX'] );
        } else {
            $ignoreIndex = '';
        }

        return [ $startOpts, $useIndex, $preLimitTail, $postLimitTail, $ignoreIndex ];
    }

    /**
     * Returns an optional GROUP BY with an optional HAVING
     *
     * @param array $options Associative array of options
     * @return string
     * @see Database::select()
     * @since 1.21
     */
    protected function makeGroupByWithHaving( $options ) {
        $sql = '';
        if ( isset( $options['GROUP BY'] ) ) {
            $gb = is_array( $options['GROUP BY'] )
                ? implode( ',', $options['GROUP BY'] )
                : $options['GROUP BY'];
            $sql .= ' GROUP BY ' . $gb;
        }
        if ( isset( $options['HAVING'] ) ) {
            $having = is_array( $options['HAVING'] )
                ? $this->makeList( $options['HAVING'], self::LIST_AND )
                : $options['HAVING'];
            $sql .= ' HAVING ' . $having;
        }

        return $sql;
    }

    /**
     * Returns an optional ORDER BY
     *
     * @param array $options Associative array of options
     * @return string
     * @see Database::select()
     * @since 1.21
     */
    protected function makeOrderBy( $options ) {
        if ( isset( $options['ORDER BY'] ) ) {
            $ob = is_array( $options['ORDER BY'] )
                ? implode( ',', $options['ORDER BY'] )
                : $options['ORDER BY'];

            return ' ORDER BY ' . $ob;
        }

        return '';
    }

    public function select(
        $table, $vars, $conds = '', $fname = __METHOD__, $options = [], $join_conds = []
    ) {
        $sql = $this->selectSQLText( $table, $vars, $conds, $fname, $options, $join_conds );

        return $this->query( $sql, $fname, self::QUERY_CHANGE_NONE );
    }

    public function selectSQLText( $table, $vars, $conds = '', $fname = __METHOD__,
        $options = [], $join_conds = []
    ) {
        if ( is_array( $vars ) ) {
            $fields = implode( ',', $this->fieldNamesWithAlias( $vars ) );
        } else {
            $fields = $vars;
        }

        $options = (array)$options;
        $useIndexes = ( isset( $options['USE INDEX'] ) && is_array( $options['USE INDEX'] ) )
            ? $options['USE INDEX']
            : [];
        $ignoreIndexes = (
            isset( $options['IGNORE INDEX'] ) &&
            is_array( $options['IGNORE INDEX'] )
        )
            ? $options['IGNORE INDEX']
            : [];

        if (
            $this->selectOptionsIncludeLocking( $options ) &&
            $this->selectFieldsOrOptionsAggregate( $vars, $options )
        ) {
            // Some DB types (e.g. postgres) disallow FOR UPDATE with aggregate
            // functions. Discourage use of such queries to encourage compatibility.
            call_user_func(
                $this->deprecationLogger,
                __METHOD__ . ": aggregation used with a locking SELECT ($fname)"
            );
        }

        if ( is_array( $table ) ) {
            if ( count( $table ) === 0 ) {
                $from = '';
            } else {
                $from = ' FROM ' .
                    $this->tableNamesWithIndexClauseOrJOIN(
                        $table, $useIndexes, $ignoreIndexes, $join_conds );
            }
        } elseif ( $table != '' ) {
            $from = ' FROM ' .
                $this->tableNamesWithIndexClauseOrJOIN(
                    [ $table ], $useIndexes, $ignoreIndexes, [] );
        } else {
            $from = '';
        }

        list( $startOpts, $useIndex, $preLimitTail, $postLimitTail, $ignoreIndex ) =
            $this->makeSelectOptions( $options );

        if ( is_array( $conds ) ) {
            $conds = $this->makeList( $conds, self::LIST_AND );
        }

        if ( $conds === null || $conds === false ) {
            $this->queryLogger->warning(
                __METHOD__
                . ' called from '
                . $fname
                . ' with incorrect parameters: $conds must be a string or an array'
            );
            $conds = '';
        }

        if ( $conds === '' || $conds === '*' ) {
            $sql = "SELECT $startOpts $fields $from $useIndex $ignoreIndex $preLimitTail";
        } elseif ( is_string( $conds ) ) {
            $sql = "SELECT $startOpts $fields $from $useIndex $ignoreIndex " .
                "WHERE $conds $preLimitTail";
        } else {
            throw new DBUnexpectedError( $this, __METHOD__ . ' called with incorrect parameters' );
        }

        if ( isset( $options['LIMIT'] ) ) {
            $sql = $this->limitResult( $sql, $options['LIMIT'],
                $options['OFFSET'] ?? false );
        }
        $sql = "$sql $postLimitTail";

        if ( isset( $options['EXPLAIN'] ) ) {
            $sql = 'EXPLAIN ' . $sql;
        }

        return $sql;
    }

    public function selectRow( $table, $vars, $conds, $fname = __METHOD__,
        $options = [], $join_conds = []
    ) {
        $options = (array)$options;
        $options['LIMIT'] = 1;

        $res = $this->select( $table, $vars, $conds, $fname, $options, $join_conds );
        if ( $res === false ) {
            throw new DBUnexpectedError( $this, "Got false from select()" );
        }

        if ( !$this->numRows( $res ) ) {
            return false;
        }

        return $this->fetchObject( $res );
    }

    public function estimateRowCount(
        $tables, $var = '*', $conds = '', $fname = __METHOD__, $options = [], $join_conds = []
    ) {
        $conds = $this->normalizeConditions( $conds, $fname );
        $column = $this->extractSingleFieldFromList( $var );
        if ( is_string( $column ) && !in_array( $column, [ '*', '1' ] ) ) {
            $conds[] = "$column IS NOT NULL";
        }

        $res = $this->select(
            $tables, [ 'rowcount' => 'COUNT(*)' ], $conds, $fname, $options, $join_conds
        );
        $row = $res ? $this->fetchRow( $res ) : [];

        return isset( $row['rowcount'] ) ? (int)$row['rowcount'] : 0;
    }

    public function selectRowCount(
        $tables, $var = '*', $conds = '', $fname = __METHOD__, $options = [], $join_conds = []
    ) {
        $conds = $this->normalizeConditions( $conds, $fname );
        $column = $this->extractSingleFieldFromList( $var );
        if ( is_string( $column ) && !in_array( $column, [ '*', '1' ] ) ) {
            $conds[] = "$column IS NOT NULL";
        }

        $res = $this->select(
            [
                'tmp_count' => $this->buildSelectSubquery(
                    $tables,
                    '1',
                    $conds,
                    $fname,
                    $options,
                    $join_conds
                )
            ],
            [ 'rowcount' => 'COUNT(*)' ],
            [],
            $fname
        );
        $row = $res ? $this->fetchRow( $res ) : [];

        return isset( $row['rowcount'] ) ? (int)$row['rowcount'] : 0;
    }

    /**
     * @param string|array $options
     * @return bool
     */
    private function selectOptionsIncludeLocking( $options ) {
        $options = (array)$options;
        foreach ( [ 'FOR UPDATE', 'LOCK IN SHARE MODE' ] as $lock ) {
            if ( in_array( $lock, $options, true ) ) {
                return true;
            }
        }

        return false;
    }

    /**
     * @param array|string $fields
     * @param array|string $options
     * @return bool
     */
    private function selectFieldsOrOptionsAggregate( $fields, $options ) {
        foreach ( (array)$options as $key => $value ) {
            if ( is_string( $key ) ) {
                if ( preg_match( '/^(?:GROUP BY|HAVING)$/i', $key ) ) {
                    return true;
                }
            } elseif ( is_string( $value ) ) {
                if ( preg_match( '/^(?:DISTINCT|DISTINCTROW)$/i', $value ) ) {
                    return true;
                }
            }
        }

        $regex = '/^(?:COUNT|MIN|MAX|SUM|GROUP_CONCAT|LISTAGG|ARRAY_AGG)\s*\\(/i';
        foreach ( (array)$fields as $field ) {
            if ( is_string( $field ) && preg_match( $regex, $field ) ) {
                return true;
            }
        }

        return false;
    }

    /**
     * @param array $rowOrRows A single (field => value) map or a list of such maps
     * @return array[] List of (field => value) maps
     * @since 1.35
     */
    final protected function normalizeRowArray( array $rowOrRows ) {
        if ( !$rowOrRows ) {
            $rows = [];
        } elseif ( isset( $rowOrRows[0] ) ) {
            $rows = $rowOrRows;
        } else {
            $rows = [ $rowOrRows ];
        }

        foreach ( $rows as $row ) {
            if ( !is_array( $row ) ) {
                throw new DBUnexpectedError( $this, "Got non-array in row array" );
            } elseif ( !$row ) {
                throw new DBUnexpectedError( $this, "Got empty array in row array" );
            }
        }

        return $rows;
    }

    /**
     * @param array|string $conds
     * @param string $fname
     * @return array
     * @since 1.31
     */
    final protected function normalizeConditions( $conds, $fname ) {
        if ( $conds === null || $conds === false ) {
            $this->queryLogger->warning(
                __METHOD__
                . ' called from '
                . $fname
                . ' with incorrect parameters: $conds must be a string or an array'
            );
            return [];
        } elseif ( $conds === '' ) {
            return [];
        }

        return is_array( $conds ) ? $conds : [ $conds ];
    }

    /**
     * @param string|string[]|string[][] $uniqueKeys Unique indexes (first is identity key)
     * @return string[][] Unique indexes as column lists (first index is the identity key)
     * @since 1.35
     */
    final protected function normalizeUpsertKeys( $uniqueKeys ) {
        if ( is_string( $uniqueKeys ) ) {
            return [ [ $uniqueKeys ] ];
        }

        if ( !is_array( $uniqueKeys ) || !$uniqueKeys ) {
            throw new DBUnexpectedError( $this, 'Invalid or empty unique key array' );
        }

        $oldStyle = false;
        $uniqueColumnSets = [];
        foreach ( $uniqueKeys as $i => $uniqueKey ) {
            if ( !is_int( $i ) ) {
                throw new DBUnexpectedError( $this, 'Unique key array should be a list' );
            } elseif ( is_string( $uniqueKey ) ) {
                $oldStyle = true;
                $uniqueColumnSets[] = [ $uniqueKey ];
            } elseif ( is_array( $uniqueKey ) && $uniqueKey ) {
                $uniqueColumnSets[] = $uniqueKey;
            } else {
                throw new DBUnexpectedError( $this, 'Invalid unique key array entry' );
            }
        }

        if ( count( $uniqueColumnSets ) > 1 ) {
            // If an existing row conflicts with new row X on key A and new row Y on key B,
            // it is not well defined how many UPDATEs should apply to the existing row and
            // in what order the new rows are checked
            $this->queryLogger->warning(
                __METHOD__ . " called with multiple unique keys",
                [ 'exception' => new RuntimeException() ]
            );
        }

        if ( $oldStyle ) {
            // Passing a list of strings for single-column unique keys is too
            // easily confused with passing the columns of composite unique key
            $this->queryLogger->warning(
                __METHOD__ . " called with deprecated parameter style: " .
                "the unique key array should be a string or array of string arrays",
                [ 'exception' => new RuntimeException() ]
            );
        }

        return $uniqueColumnSets;
    }

    /**
     * @param string|array $options
     * @return array Combination option/value map and boolean option list
     * @since 1.35
     */
    final protected function normalizeOptions( $options ) {
        if ( is_array( $options ) ) {
            return $options;
        } elseif ( is_string( $options ) ) {
            return ( $options === '' ) ? [] : [ $options ];
        } else {
            throw new DBUnexpectedError( $this, __METHOD__ . ': expected string or array' );
        }
    }

    /**
     * @param string $option Query option flag (e.g. "IGNORE" or "FOR UPDATE")
     * @param array $options Combination option/value map and boolean option list
     * @return bool Whether the option appears as an integer-keyed value in the options
     * @since 1.35
     */
    final protected function isFlagInOptions( $option, array $options ) {
        foreach ( array_keys( $options, $option, true ) as $k ) {
            if ( is_int( $k ) ) {
                return true;
            }
        }

        return false;
    }

    /**
     * @param array|string $var Field parameter in the style of select()
     * @return string|null Column name or null; ignores aliases
     */
    final protected function extractSingleFieldFromList( $var ) {
        if ( is_array( $var ) ) {
            if ( !$var ) {
                $column = null;
            } elseif ( count( $var ) == 1 ) {
                $column = $var[0] ?? reset( $var );
            } else {
                throw new DBUnexpectedError( $this, __METHOD__ . ': got multiple columns' );
            }
        } else {
            $column = $var;
        }

        return $column;
    }

    public function lockForUpdate(
        $table, $conds = '', $fname = __METHOD__, $options = [], $join_conds = []
    ) {
        if ( !$this->trxLevel() && !$this->getFlag( self::DBO_TRX ) ) {
            throw new DBUnexpectedError(
                $this,
                __METHOD__ . ': no transaction is active nor is DBO_TRX set'
            );
        }

        $options = (array)$options;
        $options[] = 'FOR UPDATE';

        return $this->selectRowCount( $table, '*', $conds, $fname, $options, $join_conds );
    }

    public function fieldExists( $table, $field, $fname = __METHOD__ ) {
        $info = $this->fieldInfo( $table, $field );

        return (bool)$info;
    }

    public function indexExists( $table, $index, $fname = __METHOD__ ) {
        if ( !$this->tableExists( $table, $fname ) ) {
            return null;
        }

        $info = $this->indexInfo( $table, $index, $fname );
        if ( $info === null ) {
            return null;
        } else {
            return $info !== false;
        }
    }

    abstract public function tableExists( $table, $fname = __METHOD__ );

    public function indexUnique( $table, $index, $fname = __METHOD__ ) {
        $indexInfo = $this->indexInfo( $table, $index, $fname );

        if ( !$indexInfo ) {
            return null;
        }

        return !$indexInfo[0]->Non_unique;
    }

    public function insert( $table, $rows, $fname = __METHOD__, $options = [] ) {
        $rows = $this->normalizeRowArray( $rows );
        if ( !$rows ) {
            return true;
        }

        $options = $this->normalizeOptions( $options );
        if ( $this->isFlagInOptions( 'IGNORE', $options ) ) {
            $this->doInsertNonConflicting( $table, $rows, $fname );
        } else {
            $this->doInsert( $table, $rows, $fname );
        }

        return true;
    }

    /**
     * @see Database::insert()
     * @param string $table
     * @param array $rows Non-empty list of rows
     * @param string $fname
     * @since 1.35
     */
    protected function doInsert( $table, array $rows, $fname ) {
        $encTable = $this->tableName( $table );
        list( $sqlColumns, $sqlTuples ) = $this->makeInsertLists( $rows );

        $sql = "INSERT INTO $encTable ($sqlColumns) VALUES $sqlTuples";

        $this->query( $sql, $fname, self::QUERY_CHANGE_ROWS );
    }

    /**
     * @see Database::insert()
     * @param string $table
     * @param array $rows Non-empty list of rows
     * @param string $fname
     * @since 1.35
     */
    protected function doInsertNonConflicting( $table, array $rows, $fname ) {
        $encTable = $this->tableName( $table );
        list( $sqlColumns, $sqlTuples ) = $this->makeInsertLists( $rows );
        list( $sqlVerb, $sqlOpts ) = $this->makeInsertNonConflictingVerbAndOptions();

        $sql = rtrim( "$sqlVerb $encTable ($sqlColumns) VALUES $sqlTuples $sqlOpts" );

        $this->query( $sql, $fname, self::QUERY_CHANGE_ROWS );
    }

    /**
     * @return string[] ("INSERT"-style SQL verb, "ON CONFLICT"-style clause or "")
     * @since 1.35
     */
    protected function makeInsertNonConflictingVerbAndOptions() {
        return [ 'INSERT IGNORE INTO', '' ];
    }

    /**
     * Make SQL lists of columns, row tuples for INSERT/VALUES expressions
     *
     * The tuple column order is that of the columns of the first provided row.
     * The provided rows must have exactly the same keys and ordering thereof.
     *
     * @param array[] $rows Non-empty list of (column => value) maps
     * @return array (comma-separated columns, comma-separated tuples)
     * @since 1.35
     */
    protected function makeInsertLists( array $rows ) {
        $firstRow = $rows[0];
        if ( !is_array( $firstRow ) || !$firstRow ) {
            throw new DBUnexpectedError( $this, 'Got an empty row list or empty row' );
        }
        // List of columns that define the value tuple ordering
        $tupleColumns = array_keys( $firstRow );

        $valueTuples = [];
        foreach ( $rows as $row ) {
            $rowColumns = array_keys( $row );
            // VALUES(...) requires a uniform correspondance of (column => value)
            if ( $rowColumns !== $tupleColumns ) {
                throw new DBUnexpectedError(
                    $this,
                    'Got row columns (' . implode( ', ', $rowColumns ) . ') ' .
                    'instead of expected (' . implode( ', ', $tupleColumns ) . ')'
                );
            }
            // Make the value tuple that defines this row
            $valueTuples[] = '(' . $this->makeList( $row, self::LIST_COMMA ) . ')';
        }

        return [
            $this->makeList( $tupleColumns, self::LIST_NAMES ),
            implode( ',', $valueTuples )
        ];
    }

    /**
     * Make UPDATE options array for Database::makeUpdateOptions
     *
     * @param array $options
     * @return array
     */
    protected function makeUpdateOptionsArray( $options ) {
        $options = $this->normalizeOptions( $options );

        $opts = [];

        if ( in_array( 'IGNORE', $options ) ) {
            $opts[] = 'IGNORE';
        }

        return $opts;
    }

    /**
     * Make UPDATE options for the Database::update function
     *
     * @param array $options The options passed to Database::update
     * @return string
     */
    protected function makeUpdateOptions( $options ) {
        $opts = $this->makeUpdateOptionsArray( $options );

        return implode( ' ', $opts );
    }

    public function update( $table, $set, $conds, $fname = __METHOD__, $options = [] ) {
        $this->assertConditionIsNotEmpty( $conds, __METHOD__, true );
        $table = $this->tableName( $table );
        $opts = $this->makeUpdateOptions( $options );
        $sql = "UPDATE $opts $table SET " . $this->makeList( $set, self::LIST_SET );

        if ( $conds && $conds !== IDatabase::ALL_ROWS ) {
            if ( is_array( $conds ) ) {
                $conds = $this->makeList( $conds, self::LIST_AND );
            }
            $sql .= ' WHERE ' . $conds;
        }

        $this->query( $sql, $fname, self::QUERY_CHANGE_ROWS );

        return true;
    }

    public function makeList( array $a, $mode = self::LIST_COMMA ) {
        $first = true;
        $list = '';

        foreach ( $a as $field => $value ) {
            if ( !$first ) {
                if ( $mode == self::LIST_AND ) {
                    $list .= ' AND ';
                } elseif ( $mode == self::LIST_OR ) {
                    $list .= ' OR ';
                } else {
                    $list .= ',';
                }
            } else {
                $first = false;
            }

            if ( ( $mode == self::LIST_AND || $mode == self::LIST_OR ) && is_numeric( $field ) ) {
                $list .= "($value)";
            } elseif ( $mode == self::LIST_SET && is_numeric( $field ) ) {
                $list .= "$value";
            } elseif (
                ( $mode == self::LIST_AND || $mode == self::LIST_OR ) && is_array( $value )
            ) {
                // Remove null from array to be handled separately if found
                $includeNull = false;
                foreach ( array_keys( $value, null, true ) as $nullKey ) {
                    $includeNull = true;
                    unset( $value[$nullKey] );
                }
                if ( count( $value ) == 0 && !$includeNull ) {
                    throw new InvalidArgumentException(
                        __METHOD__ . ": empty input for field $field" );
                } elseif ( count( $value ) == 0 ) {
                    // only check if $field is null
                    $list .= "$field IS NULL";
                } else {
                    // IN clause contains at least one valid element
                    if ( $includeNull ) {
                        // Group subconditions to ensure correct precedence
                        $list .= '(';
                    }
                    if ( count( $value ) == 1 ) {
                        // Special-case single values, as IN isn't terribly efficient
                        // Don't necessarily assume the single key is 0; we don't
                        // enforce linear numeric ordering on other arrays here.
                        $value = array_values( $value )[0];
                        $list .= $field . " = " . $this->addQuotes( $value );
                    } else {
                        $list .= $field . " IN (" . $this->makeList( $value ) . ") ";
                    }
                    // if null present in array, append IS NULL
                    if ( $includeNull ) {
                        $list .= " OR $field IS NULL)";
                    }
                }
            } elseif ( $value === null ) {
                if ( $mode == self::LIST_AND || $mode == self::LIST_OR ) {
                    $list .= "$field IS ";
                } elseif ( $mode == self::LIST_SET ) {
                    $list .= "$field = ";
                }
                $list .= 'NULL';
            } else {
                if (
                    $mode == self::LIST_AND || $mode == self::LIST_OR || $mode == self::LIST_SET
                ) {
                    $list .= "$field = ";
                }
                $list .= $mode == self::LIST_NAMES ? $value : $this->addQuotes( $value );
            }
        }

        return $list;
    }

    public function makeWhereFrom2d( $data, $baseKey, $subKey ) {
        $conds = [];

        foreach ( $data as $base => $sub ) {
            if ( count( $sub ) ) {
                $conds[] = $this->makeList(
                    [ $baseKey => $base, $subKey => array_map( 'strval', array_keys( $sub ) ) ],
                    self::LIST_AND );
            }
        }

        if ( $conds ) {
            return $this->makeList( $conds, self::LIST_OR );
        } else {
            // Nothing to search for...
            return false;
        }
    }

    public function aggregateValue( $valuedata, $valuename = 'value' ) {
        return $valuename;
    }

    public function bitNot( $field ) {
        return "(~$field)";
    }

    public function bitAnd( $fieldLeft, $fieldRight ) {
        return "($fieldLeft & $fieldRight)";
    }

    public function bitOr( $fieldLeft, $fieldRight ) {
        return "($fieldLeft | $fieldRight)";
    }

    public function buildConcat( $stringList ) {
        return 'CONCAT(' . implode( ',', $stringList ) . ')';
    }

    public function buildGroupConcatField(
        $delim, $table, $field, $conds = '', $join_conds = []
    ) {
        $fld = "GROUP_CONCAT($field SEPARATOR " . $this->addQuotes( $delim ) . ')';

        return '(' . $this->selectSQLText( $table, $fld, $conds, null, [], $join_conds ) . ')';
    }

    public function buildGreatest( $fields, $values ) {
        return $this->buildSuperlative( 'GREATEST', $fields, $values );
    }

    public function buildLeast( $fields, $values ) {
        return $this->buildSuperlative( 'LEAST', $fields, $values );
    }

    /**
     * Build a superlative function statement comparing columns/values
     *
     * Integer and float values in $values will not be quoted
     *
     * If $fields is an array, then each value with a string key is treated as an expression
     * (which must be manually quoted); such string keys do not appear in the SQL and are only
     * descriptive aliases.
     *
     * @param string $sqlfunc Name of a SQL function
     * @param string|string[] $fields Name(s) of column(s) with values to compare
     * @param string|int|float|string[]|int[]|float[] $values Values to compare
     * @return mixed
     * @since 1.35
     */
    protected function buildSuperlative( $sqlfunc, $fields, $values ) {
        $fields = is_array( $fields ) ? $fields : [ $fields ];
        $values = is_array( $values ) ? $values : [ $values ];

        $encValues = [];
        foreach ( $fields as $alias => $field ) {
            if ( is_int( $alias ) ) {
                $encValues[] = $this->addIdentifierQuotes( $field );
            } else {
                $encValues[] = $field; // expression
            }
        }
        foreach ( $values as $value ) {
            if ( is_int( $value ) || is_float( $value ) ) {
                $encValues[] = $value;
            } elseif ( is_string( $value ) ) {
                $encValues[] = $this->addQuotes( $value );
            } elseif ( $value === null ) {
                throw new DBUnexpectedError( $this, 'Null value in superlative' );
            } else {
                throw new DBUnexpectedError( $this, 'Unexpected value type in superlative' );
            }
        }

        return $sqlfunc . '(' . implode( ',', $encValues ) . ')';
    }

    public function buildSubstring( $input, $startPosition, $length = null ) {
        $this->assertBuildSubstringParams( $startPosition, $length );
        $functionBody = "$input FROM $startPosition";
        if ( $length !== null ) {
            $functionBody .= " FOR $length";
        }
        return 'SUBSTRING(' . $functionBody . ')';
    }

    /**
     * Check type and bounds for parameters to self::buildSubstring()
     *
     * All supported databases have substring functions that behave the same for
     * positive $startPosition and non-negative $length, but behaviors differ when
     * given 0 or negative $startPosition or negative $length. The simplest
     * solution to that is to just forbid those values.
     *
     * @param int $startPosition
     * @param int|null $length
     * @since 1.31
     */
    protected function assertBuildSubstringParams( $startPosition, $length ) {
        if ( !is_int( $startPosition ) || $startPosition <= 0 ) {
            throw new InvalidArgumentException(
                '$startPosition must be a positive integer'
            );
        }
        if ( !( is_int( $length ) && $length >= 0 || $length === null ) ) {
            throw new InvalidArgumentException(
                '$length must be null or an integer greater than or equal to 0'
            );
        }
    }

    /**
     * Check type and bounds conditions parameters for update
     *
     * In order to prevent possible performance or replication issues,
     * empty condition for 'update' queries isn't allowed
     *
     * @param array|string $conds conditions to be validated on emptiness
     * @param string $fname caller's function name to be passed to exception
     * @param bool $deprecate define the assertion type. If true then
     *   wfDeprecated will be called, otherwise DBUnexpectedError will be
     *   raised.
     * @since 1.35
     */
    protected function assertConditionIsNotEmpty( $conds, string $fname, bool $deprecate ) {
        $isCondValid = ( is_string( $conds ) || is_array( $conds ) ) && $conds;
        if ( !$isCondValid ) {
            if ( $deprecate ) {
                wfDeprecated( $fname . ' called with empty $conds', '1.35', false, 3 );
            } else {
                throw new DBUnexpectedError( $this, $fname . ' called with empty conditions' );
            }
        }
    }

    public function buildStringCast( $field ) {
        // In theory this should work for any standards-compliant
        // SQL implementation, although it may not be the best way to do it.
        return "CAST( $field AS CHARACTER )";
    }

    public function buildIntegerCast( $field ) {
        return 'CAST( ' . $field . ' AS INTEGER )';
    }

    public function buildSelectSubquery(
        $table, $vars, $conds = '', $fname = __METHOD__,
        $options = [], $join_conds = []
    ) {
        return new Subquery(
            $this->selectSQLText( $table, $vars, $conds, $fname, $options, $join_conds )
        );
    }

    public function databasesAreIndependent() {
        return false;
    }

    final public function selectDB( $db ) {
        $this->selectDomain( new DatabaseDomain(
            $db,
            $this->currentDomain->getSchema(),
            $this->currentDomain->getTablePrefix()
        ) );

        return true;
    }

    final public function selectDomain( $domain ) {
        $this->doSelectDomain( DatabaseDomain::newFromId( $domain ) );
    }

    /**
     * @param DatabaseDomain $domain
     * @throws DBConnectionError
     * @throws DBError
     * @since 1.32
     */
    protected function doSelectDomain( DatabaseDomain $domain ) {
        $this->currentDomain = $domain;
    }

    public function getDBname() {
        return $this->currentDomain->getDatabase();
    }

    public function getServer() {
        return $this->server;
    }

    public function tableName( $name, $format = 'quoted' ) {
        if ( $name instanceof Subquery ) {
            throw new DBUnexpectedError(
                $this,
                __METHOD__ . ': got Subquery instance when expecting a string'
            );
        }

        # Skip the entire process when we have a string quoted on both ends.
        # Note that we check the end so that we will still quote any use of
        # use of `database`.table. But won't break things if someone wants
        # to query a database table with a dot in the name.
        if ( $this->isQuotedIdentifier( $name ) ) {
            return $name;
        }

        # Lets test for any bits of text that should never show up in a table
        # name. Basically anything like JOIN or ON which are actually part of
        # SQL queries, but may end up inside of the table value to combine
        # sql. Such as how the API is doing.
        # Note that we use a whitespace test rather than a \b test to avoid
        # any remote case where a word like on may be inside of a table name
        # surrounded by symbols which may be considered word breaks.
        if ( preg_match( '/(^|\s)(DISTINCT|JOIN|ON|AS)(\s|$)/i', $name ) !== 0 ) {
            $this->queryLogger->warning(
                __METHOD__ . ": use of subqueries is not supported this way",
                [ 'exception' => new RuntimeException() ]
            );

            return $name;
        }

        # Split database and table into proper variables.
        list( $database, $schema, $prefix, $table ) = $this->qualifiedTableComponents( $name );

        # Quote $table and apply the prefix if not quoted.
        # $tableName might be empty if this is called from Database::replaceVars()
        $tableName = "{$prefix}{$table}";
        if ( $format === 'quoted'
            && !$this->isQuotedIdentifier( $tableName )
            && $tableName !== ''
        ) {
            $tableName = $this->addIdentifierQuotes( $tableName );
        }

        # Quote $schema and $database and merge them with the table name if needed
        $tableName = $this->prependDatabaseOrSchema( $schema, $tableName, $format );
        $tableName = $this->prependDatabaseOrSchema( $database, $tableName, $format );

        return $tableName;
    }

    /**
     * Get the table components needed for a query given the currently selected database
     *
     * @param string $name Table name in the form of db.schema.table, db.table, or table
     * @return array (DB name or "" for default, schema name, table prefix, table name)
     */
    protected function qualifiedTableComponents( $name ) {
        # We reverse the explode so that database.table and table both output the correct table.
        $dbDetails = explode( '.', $name, 3 );
        if ( count( $dbDetails ) == 3 ) {
            list( $database, $schema, $table ) = $dbDetails;
            # We don't want any prefix added in this case
            $prefix = '';
        } elseif ( count( $dbDetails ) == 2 ) {
            list( $database, $table ) = $dbDetails;
            # We don't want any prefix added in this case
            $prefix = '';
            # In dbs that support it, $database may actually be the schema
            # but that doesn't affect any of the functionality here
            $schema = '';
        } else {
            list( $table ) = $dbDetails;
            if ( isset( $this->tableAliases[$table] ) ) {
                $database = $this->tableAliases[$table]['dbname'];
                $schema = is_string( $this->tableAliases[$table]['schema'] )
                    ? $this->tableAliases[$table]['schema']
                    : $this->relationSchemaQualifier();
                $prefix = is_string( $this->tableAliases[$table]['prefix'] )
                    ? $this->tableAliases[$table]['prefix']
                    : $this->tablePrefix();
            } else {
                $database = '';
                $schema = $this->relationSchemaQualifier(); # Default schema
                $prefix = $this->tablePrefix(); # Default prefix
            }
        }

        return [ $database, $schema, $prefix, $table ];
    }

    /**
     * @param string|null $namespace Database or schema
     * @param string $relation Name of table, view, sequence, etc...
     * @param string $format One of (raw, quoted)
     * @return string Relation name with quoted and merged $namespace as needed
     */
    private function prependDatabaseOrSchema( $namespace, $relation, $format ) {
        if ( strlen( $namespace ) ) {
            if ( $format === 'quoted' && !$this->isQuotedIdentifier( $namespace ) ) {
                $namespace = $this->addIdentifierQuotes( $namespace );
            }
            $relation = $namespace . '.' . $relation;
        }

        return $relation;
    }

    public function tableNames( ...$tables ) {
        $retVal = [];

        foreach ( $tables as $name ) {
            $retVal[$name] = $this->tableName( $name );
        }

        return $retVal;
    }

    public function tableNamesN( ...$tables ) {
        $retVal = [];

        foreach ( $tables as $name ) {
            $retVal[] = $this->tableName( $name );
        }

        return $retVal;
    }

    /**
     * Get an aliased table name
     *
     * This returns strings like "tableName AS newTableName" for aliased tables
     * and "(SELECT * from tableA) newTablename" for subqueries (e.g. derived tables)
     *
     * @see Database::tableName()
     * @param string|Subquery $table Table name or object with a 'sql' field
     * @param string|bool $alias Table alias (optional)
     * @return string SQL name for aliased table. Will not alias a table to its own name
     */
    protected function tableNameWithAlias( $table, $alias = false ) {
        if ( is_string( $table ) ) {
            $quotedTable = $this->tableName( $table );
        } elseif ( $table instanceof Subquery ) {
            $quotedTable = (string)$table;
        } else {
            throw new InvalidArgumentException( "Table must be a string or Subquery" );
        }

        if ( $alias === false || $alias === $table ) {
            if ( $table instanceof Subquery ) {
                throw new InvalidArgumentException( "Subquery table missing alias" );
            }

            return $quotedTable;
        } else {
            return $quotedTable . ' ' . $this->addIdentifierQuotes( $alias );
        }
    }

    /**
     * Get an aliased field name
     * e.g. fieldName AS newFieldName
     *
     * @param string $name Field name
     * @param string|bool $alias Alias (optional)
     * @return string SQL name for aliased field. Will not alias a field to its own name
     */
    protected function fieldNameWithAlias( $name, $alias = false ) {
        if ( !$alias || (string)$alias === (string)$name ) {
            return $name;
        } else {
            return $name . ' AS ' . $this->addIdentifierQuotes( $alias ); // PostgreSQL needs AS
        }
    }

    /**
     * Gets an array of aliased field names
     *
     * @param array $fields [ [alias] => field ]
     * @return string[] See fieldNameWithAlias()
     */
    protected function fieldNamesWithAlias( $fields ) {
        $retval = [];
        foreach ( $fields as $alias => $field ) {
            if ( is_numeric( $alias ) ) {
                $alias = $field;
            }
            $retval[] = $this->fieldNameWithAlias( $field, $alias );
        }

        return $retval;
    }

    /**
     * Get the aliased table name clause for a FROM clause
     * which might have a JOIN and/or USE INDEX or IGNORE INDEX clause
     *
     * @param array $tables ( [alias] => table )
     * @param array $use_index Same as for select()
     * @param array $ignore_index Same as for select()
     * @param array $join_conds Same as for select()
     * @return string
     */
    protected function tableNamesWithIndexClauseOrJOIN(
        $tables, $use_index = [], $ignore_index = [], $join_conds = []
    ) {
        $ret = [];
        $retJOIN = [];
        $use_index = (array)$use_index;
        $ignore_index = (array)$ignore_index;
        $join_conds = (array)$join_conds;

        foreach ( $tables as $alias => $table ) {
            if ( !is_string( $alias ) ) {
                // No alias? Set it equal to the table name
                $alias = $table;
            }

            if ( is_array( $table ) ) {
                // A parenthesized group
                if ( count( $table ) > 1 ) {
                    $joinedTable = '(' .
                        $this->tableNamesWithIndexClauseOrJOIN(
                            $table, $use_index, $ignore_index, $join_conds ) . ')';
                } else {
                    // Degenerate case
                    $innerTable = reset( $table );
                    $innerAlias = key( $table );
                    $joinedTable = $this->tableNameWithAlias(
                        $innerTable,
                        is_string( $innerAlias ) ? $innerAlias : $innerTable
                    );
                }
            } else {
                $joinedTable = $this->tableNameWithAlias( $table, $alias );
            }

            // Is there a JOIN clause for this table?
            if ( isset( $join_conds[$alias] ) ) {
                list( $joinType, $conds ) = $join_conds[$alias];
                $tableClause = $joinType;
                $tableClause .= ' ' . $joinedTable;
                if ( isset( $use_index[$alias] ) ) { // has USE INDEX?
                    $use = $this->useIndexClause( implode( ',', (array)$use_index[$alias] ) );
                    if ( $use != '' ) {
                        $tableClause .= ' ' . $use;
                    }
                }
                if ( isset( $ignore_index[$alias] ) ) { // has IGNORE INDEX?
                    $ignore = $this->ignoreIndexClause(
                        implode( ',', (array)$ignore_index[$alias] ) );
                    if ( $ignore != '' ) {
                        $tableClause .= ' ' . $ignore;
                    }
                }
                $on = $this->makeList( (array)$conds, self::LIST_AND );
                if ( $on != '' ) {
                    $tableClause .= ' ON (' . $on . ')';
                }

                $retJOIN[] = $tableClause;
            } elseif ( isset( $use_index[$alias] ) ) {
                // Is there an INDEX clause for this table?
                $tableClause = $joinedTable;
                $tableClause .= ' ' . $this->useIndexClause(
                        implode( ',', (array)$use_index[$alias] )
                    );

                $ret[] = $tableClause;
            } elseif ( isset( $ignore_index[$alias] ) ) {
                // Is there an INDEX clause for this table?
                $tableClause = $joinedTable;
                $tableClause .= ' ' . $this->ignoreIndexClause(
                        implode( ',', (array)$ignore_index[$alias] )
                    );

                $ret[] = $tableClause;
            } else {
                $tableClause = $joinedTable;

                $ret[] = $tableClause;
            }
        }

        // We can't separate explicit JOIN clauses with ',', use ' ' for those
        $implicitJoins = implode( ',', $ret );
        $explicitJoins = implode( ' ', $retJOIN );

        // Compile our final table clause
        return implode( ' ', [ $implicitJoins, $explicitJoins ] );
    }

    /**
     * Allows for index remapping in queries where this is not consistent across DBMS
     *
     * @param string $index
     * @return string
     */
    protected function indexName( $index ) {
        return $this->indexAliases[$index] ?? $index;
    }

    public function addQuotes( $s ) {
        if ( $s instanceof Blob ) {
            $s = $s->fetch();
        }
        if ( $s === null ) {
            return 'NULL';
        } elseif ( is_bool( $s ) ) {
            return (string)(int)$s;
        } elseif ( is_int( $s ) ) {
            return (string)$s;
        } else {
            return "'" . $this->strencode( $s ) . "'";
        }
    }

    public function addIdentifierQuotes( $s ) {
        return '"' . str_replace( '"', '""', $s ) . '"';
    }

    /**
     * Returns if the given identifier looks quoted or not according to
     * the database convention for quoting identifiers .
     *
     * @note Do not use this to determine if untrusted input is safe.
     *   A malicious user can trick this function.
     * @param string $name
     * @return bool
     */
    public function isQuotedIdentifier( $name ) {
        return $name[0] == '"' && substr( $name, -1, 1 ) == '"';
    }

    /**
     * @param string $s
     * @param string $escapeChar
     * @return string
     */
    protected function escapeLikeInternal( $s, $escapeChar = '`' ) {
        return str_replace( [ $escapeChar, '%', '_' ],
            [ "{$escapeChar}{$escapeChar}", "{$escapeChar}%", "{$escapeChar}_" ],
            $s );
    }

    public function buildLike( $param, ...$params ) {
        if ( is_array( $param ) ) {
            $params = $param;
        } else {
            $params = func_get_args();
        }

        $s = '';

        // We use ` instead of \ as the default LIKE escape character, since addQuotes()
        // may escape backslashes, creating problems of double escaping. The `
        // character has good cross-DBMS compatibility, avoiding special operators
        // in MS SQL like ^ and %
        $escapeChar = '`';

        foreach ( $params as $value ) {
            if ( $value instanceof LikeMatch ) {
                $s .= $value->toString();
            } else {
                $s .= $this->escapeLikeInternal( $value, $escapeChar );
            }
        }

        return ' LIKE ' .
            $this->addQuotes( $s ) . ' ESCAPE ' . $this->addQuotes( $escapeChar ) . ' ';
    }

    public function anyChar() {
        return new LikeMatch( '_' );
    }

    public function anyString() {
        return new LikeMatch( '%' );
    }

    public function nextSequenceValue( $seqName ) {
        return null;
    }

    /**
     * USE INDEX clause. Unlikely to be useful for anything but MySQL. This
     * is only needed because a) MySQL must be as efficient as possible due to
     * its use on Wikipedia, and b) MySQL 4.0 is kind of dumb sometimes about
     * which index to pick. Anyway, other databases might have different
     * indexes on a given table. So don't bother overriding this unless you're
     * MySQL.
     * @param string $index
     * @return string
     */
    public function useIndexClause( $index ) {
        return '';
    }

    /**
     * IGNORE INDEX clause. Unlikely to be useful for anything but MySQL. This
     * is only needed because a) MySQL must be as efficient as possible due to
     * its use on Wikipedia, and b) MySQL 4.0 is kind of dumb sometimes about
     * which index to pick. Anyway, other databases might have different
     * indexes on a given table. So don't bother overriding this unless you're
     * MySQL.
     * @param string $index
     * @return string
     */
    public function ignoreIndexClause( $index ) {
        return '';
    }

    public function replace( $table, $uniqueKeys, $rows, $fname = __METHOD__ ) {
        $rows = $this->normalizeRowArray( $rows );
        if ( !$rows ) {
            return;
        }

        if ( $uniqueKeys ) {
            $uniqueKeys = $this->normalizeUpsertKeys( $uniqueKeys );
            $this->doReplace( $table, $uniqueKeys, $rows, $fname );
        } else {
            $this->queryLogger->warning(
                __METHOD__ . " called with no unique keys",
                [ 'exception' => new RuntimeException() ]
            );
            $this->doInsert( $table, $rows, $fname );
        }
    }

    /**
     * @see Database::replace()
     * @param string $table
     * @param string[][] $uniqueKeys Non-empty list of unique keys
     * @param array $rows Non-empty list of rows
     * @param string $fname
     * @since 1.35
     */
    protected function doReplace( $table, array $uniqueKeys, array $rows, $fname ) {
        $affectedRowCount = 0;
        $this->startAtomic( $fname, self::ATOMIC_CANCELABLE );
        try {
            foreach ( $rows as $row ) {
                // Delete any conflicting rows (including ones inserted from $rows)
                $sqlCondition = $this->makeConditionCollidesUponKeys( [ $row ], $uniqueKeys );
                $this->delete( $table, [ $sqlCondition ], $fname );
                $affectedRowCount += $this->affectedRows();
                // Now insert the row
                $this->insert( $table, $row, $fname );
                $affectedRowCount += $this->affectedRows();
            }
            $this->endAtomic( $fname );
        } catch ( Throwable $e ) {
            $this->cancelAtomic( $fname );
            throw $e;
        }
        $this->affectedRowCount = $affectedRowCount;
    }

    /**
     * @param array[] $rows Non-empty list of rows
     * @param string[] $uniqueKey List of columns that define a single unique index
     * @return string SQL conditions to filter existing rows to those with counterparts in $rows
     */
    private function makeConditionCollidesUponKey( array $rows, array $uniqueKey ) {
        if ( !$rows ) {
            throw new DBUnexpectedError( $this, "Empty row array" );
        } elseif ( !$uniqueKey ) {
            throw new DBUnexpectedError( $this, "Empty unique key array" );
        }

        if ( count( $uniqueKey ) == 1 ) {
            // Use a simple IN(...) clause
            $column = reset( $uniqueKey );
            $values = array_column( $rows, $column );
            if ( count( $values ) !== count( $rows ) ) {
                throw new DBUnexpectedError( $this, "Missing values for unique key ($column)" );
            }

            return $this->makeList( [ $column => $values ], self::LIST_AND );
        }

        $disjunctions = [];
        foreach ( $rows as $row ) {
            $rowKeyMap = array_intersect_key( $row, array_flip( $uniqueKey ) );
            if ( count( $rowKeyMap ) != count( $uniqueKey ) ) {
                throw new DBUnexpectedError(
                    $this,
                    "Missing values for unique key (" . implode( ',', $uniqueKey ) . ")"
                );
            }
            $disjunctions[] = $this->makeList( $rowKeyMap, self::LIST_AND );
        }

        return count( $disjunctions ) > 1
            ? $this->makeList( $disjunctions, self::LIST_OR )
            : $disjunctions[0];
    }

    /**
     * @param array[] $rows Non-empty list of rows
     * @param string[][] $uniqueKeys List of column lists that each define a unique index
     * @return string SQL conditions to filter existing rows to those with counterparts in $rows
     * @since 1.35
     */
    final protected function makeConditionCollidesUponKeys( array $rows, array $uniqueKeys ) {
        if ( !$uniqueKeys ) {
            throw new DBUnexpectedError( $this, "Empty unique key array" );
        }

        $disjunctions = [];
        foreach ( $uniqueKeys as $uniqueKey ) {
            $disjunctions[] = $this->makeConditionCollidesUponKey( $rows, $uniqueKey );
        }

        return count( $disjunctions ) > 1
            ? $this->makeList( $disjunctions, self::LIST_OR )
            : $disjunctions[0];
    }

    public function upsert( $table, array $rows, $uniqueKeys, array $set, $fname = __METHOD__ ) {
        $rows = $this->normalizeRowArray( $rows );
        if ( !$rows ) {
            return true;
        }

        if ( $uniqueKeys ) {
            $uniqueKeys = $this->normalizeUpsertKeys( $uniqueKeys );
            $this->doUpsert( $table, $rows, $uniqueKeys, $set, $fname );
        } else {
            $this->queryLogger->warning(
                __METHOD__ . " called with no unique keys",
                [ 'exception' => new RuntimeException() ]
            );
            $this->doInsert( $table, $rows, $fname );
        }

        return true;
    }

    /**
     * @see Database::upsert()
     * @param string $table
     * @param array[] $rows Non-empty list of rows
     * @param string[][] $uniqueKeys Non-empty list of unique keys
     * @param array $set
     * @param string $fname
     * @since 1.35
     */
    protected function doUpsert( $table, array $rows, array $uniqueKeys, array $set, $fname ) {
        $affectedRowCount = 0;
        $this->startAtomic( $fname, self::ATOMIC_CANCELABLE );
        try {
            foreach ( $rows as $row ) {
                // Update any existing conflicting rows (including ones inserted from $rows)
                $sqlConditions = $this->makeConditionCollidesUponKeys( [ $row ], $uniqueKeys );
                $this->update( $table, $set, [ $sqlConditions ], $fname );
                $rowsUpdated = $this->affectedRows();
                $affectedRowCount += $rowsUpdated;
                if ( $rowsUpdated <= 0 ) {
                    // Now insert the row if there are no conflicts
                    $this->insert( $table, $row, $fname );
                    $affectedRowCount += $this->affectedRows();
                }
            }
            $this->endAtomic( $fname );
        } catch ( Throwable $e ) {
            $this->cancelAtomic( $fname );
            throw $e;
        }
        $this->affectedRowCount = $affectedRowCount;
    }

    public function deleteJoin( $delTable, $joinTable, $delVar, $joinVar, $conds,
        $fname = __METHOD__
    ) {
        if ( !$conds ) {
            throw new DBUnexpectedError( $this, __METHOD__ . ' called with empty $conds' );
        }

        $delTable = $this->tableName( $delTable );
        $joinTable = $this->tableName( $joinTable );
        $sql = "DELETE FROM $delTable WHERE $delVar IN (SELECT $joinVar FROM $joinTable ";
        if ( $conds != '*' ) {
            $sql .= 'WHERE ' . $this->makeList( $conds, self::LIST_AND );
        }
        $sql .= ')';

        $this->query( $sql, $fname, self::QUERY_CHANGE_ROWS );
    }

    public function textFieldSize( $table, $field ) {
        $table = $this->tableName( $table );
        $sql = "SHOW COLUMNS FROM $table LIKE \"$field\"";
        $res = $this->query( $sql, __METHOD__, self::QUERY_CHANGE_NONE );
        $row = $this->fetchObject( $res );

        $m = [];

        if ( preg_match( '/\((.*)\)/', $row->Type, $m ) ) {
            $size = $m[1];
        } else {
            $size = -1;
        }

        return $size;
    }

    public function delete( $table, $conds, $fname = __METHOD__ ) {
        $this->assertConditionIsNotEmpty( $conds, __METHOD__, false );

        $table = $this->tableName( $table );
        $sql = "DELETE FROM $table";

        if ( $conds !== IDatabase::ALL_ROWS ) {
            if ( is_array( $conds ) ) {
                $conds = $this->makeList( $conds, self::LIST_AND );
            }
            $sql .= ' WHERE ' . $conds;
        }

        $this->query( $sql, $fname, self::QUERY_CHANGE_ROWS );

        return true;
    }

    final public function insertSelect(
        $destTable,
        $srcTable,
        $varMap,
        $conds,
        $fname = __METHOD__,
        $insertOptions = [],
        $selectOptions = [],
        $selectJoinConds = []
    ) {
        static $hints = [ 'NO_AUTO_COLUMNS' ];

        $insertOptions = $this->normalizeOptions( $insertOptions );
        $selectOptions = $this->normalizeOptions( $selectOptions );

        if ( $this->cliMode && $this->isInsertSelectSafe( $insertOptions, $selectOptions ) ) {
            // For massive migrations with downtime, we don't want to select everything
            // into memory and OOM, so do all this native on the server side if possible.
            $this->doInsertSelectNative(
                $destTable,
                $srcTable,
                $varMap,
                $conds,
                $fname,
                array_diff( $insertOptions, $hints ),
                $selectOptions,
                $selectJoinConds
            );
        } else {
            $this->doInsertSelectGeneric(
                $destTable,
                $srcTable,
                $varMap,
                $conds,
                $fname,
                array_diff( $insertOptions, $hints ),
                $selectOptions,
                $selectJoinConds
            );
        }

        return true;
    }

    /**
     * @param array $insertOptions INSERT options
     * @param array $selectOptions SELECT options
     * @return bool Whether an INSERT SELECT with these options will be replication safe
     * @since 1.31
     */
    protected function isInsertSelectSafe( array $insertOptions, array $selectOptions ) {
        return true;
    }

    /**
     * Implementation of insertSelect() based on select() and insert()
     *
     * @see IDatabase::insertSelect()
     * @param string $destTable
     * @param string|array $srcTable
     * @param array $varMap
     * @param array $conds
     * @param string $fname
     * @param array $insertOptions
     * @param array $selectOptions
     * @param array $selectJoinConds
     * @since 1.35
     */
    protected function doInsertSelectGeneric(
        $destTable,
        $srcTable,
        array $varMap,
        $conds,
        $fname,
        array $insertOptions,
        array $selectOptions,
        $selectJoinConds
    ) {
        // For web requests, do a locking SELECT and then INSERT. This puts the SELECT burden
        // on only the master (without needing row-based-replication). It also makes it easy to
        // know how big the INSERT is going to be.
        $fields = [];
        foreach ( $varMap as $dstColumn => $sourceColumnOrSql ) {
            $fields[] = $this->fieldNameWithAlias( $sourceColumnOrSql, $dstColumn );
        }
        $res = $this->select(
            $srcTable,
            implode( ',', $fields ),
            $conds,
            $fname,
            array_merge( $selectOptions, [ 'FOR UPDATE' ] ),
            $selectJoinConds
        );
        if ( !$res ) {
            return;
        }

        $affectedRowCount = 0;
        $this->startAtomic( $fname, self::ATOMIC_CANCELABLE );
        try {
            $rows = [];
            foreach ( $res as $row ) {
                $rows[] = (array)$row;
            }
            // Avoid inserts that are too huge
            $rowBatches = array_chunk( $rows, $this->nonNativeInsertSelectBatchSize );
            foreach ( $rowBatches as $rows ) {
                $this->insert( $destTable, $rows, $fname, $insertOptions );
                $affectedRowCount += $this->affectedRows();
            }
        } catch ( Throwable $e ) {
            $this->cancelAtomic( $fname );
            throw $e;
        }
        $this->endAtomic( $fname );
        $this->affectedRowCount = $affectedRowCount;
    }

    /**
     * Native server-side implementation of insertSelect() for situations where
     * we don't want to select everything into memory
     *
     * @see IDatabase::insertSelect()
     * @param string $destTable
     * @param string|array $srcTable
     * @param array $varMap
     * @param array $conds
     * @param string $fname
     * @param array $insertOptions
     * @param array $selectOptions
     * @param array $selectJoinConds
     * @since 1.35
     */
    protected function doInsertSelectNative(
        $destTable,
        $srcTable,
        array $varMap,
        $conds,
        $fname,
        array $insertOptions,
        array $selectOptions,
        $selectJoinConds
    ) {
        list( $sqlVerb, $sqlOpts ) = $this->isFlagInOptions( 'IGNORE', $insertOptions )
            ? $this->makeInsertNonConflictingVerbAndOptions()
            : [ 'INSERT INTO', '' ];
        $encDstTable = $this->tableName( $destTable );
        $sqlDstColumns = implode( ',', array_keys( $varMap ) );
        $selectSql = $this->selectSQLText(
            $srcTable,
            array_values( $varMap ),
            $conds,
            $fname,
            $selectOptions,
            $selectJoinConds
        );

        $sql = rtrim( "$sqlVerb $encDstTable ($sqlDstColumns) $selectSql $sqlOpts" );

        $this->query( $sql, $fname, self::QUERY_CHANGE_ROWS );
    }

    public function limitResult( $sql, $limit, $offset = false ) {
        if ( !is_numeric( $limit ) ) {
            throw new DBUnexpectedError(
                $this,
                "Invalid non-numeric limit passed to " . __METHOD__
            );
        }
        // This version works in MySQL and SQLite. It will very likely need to be
        // overridden for most other RDBMS subclasses.
        return "$sql LIMIT "
            . ( ( is_numeric( $offset ) && $offset != 0 ) ? "{$offset}," : "" )
            . "{$limit} ";
    }

    public function unionSupportsOrderAndLimit() {
        return true; // True for almost every DB supported
    }

    public function unionQueries( $sqls, $all ) {
        $glue = $all ? ') UNION ALL (' : ') UNION (';

        return '(' . implode( $glue, $sqls ) . ')';
    }

    public function unionConditionPermutations(
        $table, $vars, array $permute_conds, $extra_conds = '', $fname = __METHOD__,
        $options = [], $join_conds = []
    ) {
        // First, build the Cartesian product of $permute_conds
        $conds = [ [] ];
        foreach ( $permute_conds as $field => $values ) {
            if ( !$values ) {
                // Skip empty $values
                continue;
            }
            $values = array_unique( $values ); // For sanity
            $newConds = [];
            foreach ( $conds as $cond ) {
                foreach ( $values as $value ) {
                    $cond[$field] = $value;
                    $newConds[] = $cond; // Arrays are by-value, not by-reference, so this works
                }
            }
            $conds = $newConds;
        }

        $extra_conds = $extra_conds === '' ? [] : (array)$extra_conds;

        // If there's just one condition and no subordering, hand off to
        // selectSQLText directly.
        if ( count( $conds ) === 1 &&
            ( !isset( $options['INNER ORDER BY'] ) || !$this->unionSupportsOrderAndLimit() )
        ) {
            return $this->selectSQLText(
                $table, $vars, $conds[0] + $extra_conds, $fname, $options, $join_conds
            );
        }

        // Otherwise, we need to pull out the order and limit to apply after
        // the union. Then build the SQL queries for each set of conditions in
        // $conds. Then union them together (using UNION ALL, because the
        // product *should* already be distinct).
        $orderBy = $this->makeOrderBy( $options );
        $limit = $options['LIMIT'] ?? null;
        $offset = $options['OFFSET'] ?? false;
        $all = empty( $options['NOTALL'] ) && !in_array( 'NOTALL', $options );
        if ( !$this->unionSupportsOrderAndLimit() ) {
            unset( $options['ORDER BY'], $options['LIMIT'], $options['OFFSET'] );
        } else {
            if ( array_key_exists( 'INNER ORDER BY', $options ) ) {
                $options['ORDER BY'] = $options['INNER ORDER BY'];
            }
            if ( $limit !== null && is_numeric( $offset ) && $offset != 0 ) {
                // We need to increase the limit by the offset rather than
                // using the offset directly, otherwise it'll skip incorrectly
                // in the subqueries.
                $options['LIMIT'] = $limit + $offset;
                unset( $options['OFFSET'] );
            }
        }

        $sqls = [];
        foreach ( $conds as $cond ) {
            $sqls[] = $this->selectSQLText(
                $table, $vars, $cond + $extra_conds, $fname, $options, $join_conds
            );
        }
        $sql = $this->unionQueries( $sqls, $all ) . $orderBy;
        if ( $limit !== null ) {
            $sql = $this->limitResult( $sql, $limit, $offset );
        }

        return $sql;
    }

    public function conditional( $cond, $trueVal, $falseVal ) {
        if ( is_array( $cond ) ) {
            $cond = $this->makeList( $cond, self::LIST_AND );
        }

        return " (CASE WHEN $cond THEN $trueVal ELSE $falseVal END) ";
    }

    public function strreplace( $orig, $old, $new ) {
        return "REPLACE({$orig}, {$old}, {$new})";
    }

    public function getServerUptime() {
        return 0;
    }

    public function wasDeadlock() {
        return false;
    }

    public function wasLockTimeout() {
        return false;
    }

    public function wasConnectionLoss() {
        return $this->wasConnectionError( $this->lastErrno() );
    }

    public function wasReadOnlyError() {
        return false;
    }

    public function wasErrorReissuable() {
        return (
            $this->wasDeadlock() ||
            $this->wasLockTimeout() ||
            $this->wasConnectionLoss()
        );
    }

    /**
     * Do not use this method outside of Database/DBError classes
     *
     * @param int|string $errno
     * @return bool Whether the given query error was a connection drop
     */
    public function wasConnectionError( $errno ) {
        return false;
    }

    /**
     * @return bool Whether it is known that the last query error only caused statement rollback
     * @note This is for backwards compatibility for callers catching DBError exceptions in
     *   order to ignore problems like duplicate key errors or foriegn key violations
     * @since 1.31
     */
    protected function wasKnownStatementRollbackError() {
        return false; // don't know; it could have caused a transaction rollback
    }

    public function deadlockLoop( ...$args ) {
        $function = array_shift( $args );
        $tries = self::$DEADLOCK_TRIES;

        $this->begin( __METHOD__ );

        $retVal = null;
        /** @var Throwable $e */
        $e = null;
        do {
            try {
                $retVal = $function( ...$args );
                break;
            } catch ( DBQueryError $e ) {
                if ( $this->wasDeadlock() ) {
                    // Retry after a randomized delay
                    usleep( mt_rand( self::$DEADLOCK_DELAY_MIN, self::$DEADLOCK_DELAY_MAX ) );
                } else {
                    // Throw the error back up
                    throw $e;
                }
            }
        } while ( --$tries > 0 );

        if ( $tries <= 0 ) {
            // Too many deadlocks; give up
            $this->rollback( __METHOD__ );
            throw $e;
        } else {
            $this->commit( __METHOD__ );

            return $retVal;
        }
    }

    public function masterPosWait( DBMasterPos $pos, $timeout ) {
        # Real waits are implemented in the subclass.
        return 0;
    }

    public function getReplicaPos() {
        # Stub
        return false;
    }

    public function getMasterPos() {
        # Stub
        return false;
    }

    public function serverIsReadOnly() {
        return false;
    }

    final public function onTransactionResolution( callable $callback, $fname = __METHOD__ ) {
        if ( !$this->trxLevel() ) {
            throw new DBUnexpectedError( $this, "No transaction is active" );
        }
        $this->trxEndCallbacks[] = [ $callback, $fname, $this->currentAtomicSectionId() ];
    }

    final public function onTransactionCommitOrIdle( callable $callback, $fname = __METHOD__ ) {
        if ( !$this->trxLevel() && $this->getTransactionRoundId() ) {
            // Start an implicit transaction similar to how query() does
            $this->begin( __METHOD__, self::TRANSACTION_INTERNAL );
            $this->trxAutomatic = true;
        }

        $this->trxIdleCallbacks[] = [ $callback, $fname, $this->currentAtomicSectionId() ];
        if ( !$this->trxLevel() ) {
            $this->runOnTransactionIdleCallbacks( self::TRIGGER_IDLE );
        }
    }

    final public function onTransactionIdle( callable $callback, $fname = __METHOD__ ) {
        $this->onTransactionCommitOrIdle( $callback, $fname );
    }

    final public function onTransactionPreCommitOrIdle( callable $callback, $fname = __METHOD__ ) {
        if ( !$this->trxLevel() && $this->getTransactionRoundId() ) {
            // Start an implicit transaction similar to how query() does
            $this->begin( __METHOD__, self::TRANSACTION_INTERNAL );
            $this->trxAutomatic = true;
        }

        if ( $this->trxLevel() ) {
            $this->trxPreCommitCallbacks[] = [ $callback, $fname, $this->currentAtomicSectionId() ];
        } else {
            // No transaction is active nor will start implicitly, so make one for this callback
            $this->startAtomic( __METHOD__, self::ATOMIC_CANCELABLE );
            try {
                $callback( $this );
                $this->endAtomic( __METHOD__ );
            } catch ( Throwable $e ) {
                $this->cancelAtomic( __METHOD__ );
                throw $e;
            }
        }
    }

    final public function onAtomicSectionCancel( callable $callback, $fname = __METHOD__ ) {
        if ( !$this->trxLevel() || !$this->trxAtomicLevels ) {
            throw new DBUnexpectedError( $this, "No atomic section is open (got $fname)" );
        }
        $this->trxSectionCancelCallbacks[] = [ $callback, $fname, $this->currentAtomicSectionId() ];
    }

    /**
     * @return AtomicSectionIdentifier|null ID of the topmost atomic section level
     */
    private function currentAtomicSectionId() {
        if ( $this->trxLevel() && $this->trxAtomicLevels ) {
            $levelInfo = end( $this->trxAtomicLevels );

            return $levelInfo[1];
        }

        return null;
    }

    /**
     * Hoist callback ownership for callbacks in a section to a parent section.
     * All callbacks should have an owner that is present in trxAtomicLevels.
     * @param AtomicSectionIdentifier $old
     * @param AtomicSectionIdentifier $new
     */
    private function reassignCallbacksForSection(
        AtomicSectionIdentifier $old, AtomicSectionIdentifier $new
    ) {
        foreach ( $this->trxPreCommitCallbacks as $key => $info ) {
            if ( $info[2] === $old ) {
                $this->trxPreCommitCallbacks[$key][2] = $new;
            }
        }
        foreach ( $this->trxIdleCallbacks as $key => $info ) {
            if ( $info[2] === $old ) {
                $this->trxIdleCallbacks[$key][2] = $new;
            }
        }
        foreach ( $this->trxEndCallbacks as $key => $info ) {
            if ( $info[2] === $old ) {
                $this->trxEndCallbacks[$key][2] = $new;
            }
        }
        foreach ( $this->trxSectionCancelCallbacks as $key => $info ) {
            if ( $info[2] === $old ) {
                $this->trxSectionCancelCallbacks[$key][2] = $new;
            }
        }
    }

    /**
     * Update callbacks that were owned by cancelled atomic sections.
     *
     * Callbacks for "on commit" should never be run if they're owned by a
     * section that won't be committed.
     *
     * Callbacks for "on resolution" need to reflect that the section was
     * rolled back, even if the transaction as a whole commits successfully.
     *
     * Callbacks for "on section cancel" should already have been consumed,
     * but errors during the cancellation itself can prevent that while still
     * destroying the section. Hoist any such callbacks to the new top section,
     * which we assume will itself have to be cancelled or rolled back to
     * resolve the error.
     *
     * @param AtomicSectionIdentifier[] $sectionIds ID of an actual savepoint
     * @param AtomicSectionIdentifier|null $newSectionId New top section ID.
     * @throws UnexpectedValueException
     */
    private function modifyCallbacksForCancel(
        array $sectionIds, AtomicSectionIdentifier $newSectionId = null
    ) {
        // Cancel the "on commit" callbacks owned by this savepoint
        $this->trxIdleCallbacks = array_filter(
            $this->trxIdleCallbacks,
            function ( $entry ) use ( $sectionIds ) {
                return !in_array( $entry[2], $sectionIds, true );
            }
        );
        $this->trxPreCommitCallbacks = array_filter(
            $this->trxPreCommitCallbacks,
            function ( $entry ) use ( $sectionIds ) {
                return !in_array( $entry[2], $sectionIds, true );
            }
        );
        // Make "on resolution" callbacks owned by this savepoint to perceive a rollback
        foreach ( $this->trxEndCallbacks as $key => $entry ) {
            if ( in_array( $entry[2], $sectionIds, true ) ) {
                $callback = $entry[0];
                $this->trxEndCallbacks[$key][0] = function () use ( $callback ) {
                    return $callback( self::TRIGGER_ROLLBACK, $this );
                };
                // This "on resolution" callback no longer belongs to a section.
                $this->trxEndCallbacks[$key][2] = null;
            }
        }
        // Hoist callback ownership for section cancel callbacks to the new top section
        foreach ( $this->trxSectionCancelCallbacks as $key => $entry ) {
            if ( in_array( $entry[2], $sectionIds, true ) ) {
                $this->trxSectionCancelCallbacks[$key][2] = $newSectionId;
            }
        }
    }

    final public function setTransactionListener( $name, callable $callback = null ) {
        if ( $callback ) {
            $this->trxRecurringCallbacks[$name] = $callback;
        } else {
            unset( $this->trxRecurringCallbacks[$name] );
        }
    }

    /**
     * Whether to disable running of post-COMMIT/ROLLBACK callbacks
     *
     * This method should not be used outside of Database/LoadBalancer
     *
     * @param bool $suppress
     * @since 1.28
     */
    final public function setTrxEndCallbackSuppression( $suppress ) {
        $this->trxEndCallbacksSuppressed = $suppress;
    }

    /**
     * Actually consume and run any "on transaction idle/resolution" callbacks.
     *
     * This method should not be used outside of Database/LoadBalancer
     *
     * @param int $trigger IDatabase::TRIGGER_* constant
     * @return int Number of callbacks attempted
     * @since 1.20
     * @throws Exception
     */
    public function runOnTransactionIdleCallbacks( $trigger ) {
        if ( $this->trxLevel() ) { // sanity
            throw new DBUnexpectedError( $this, __METHOD__ . ': a transaction is still open' );
        }

        if ( $this->trxEndCallbacksSuppressed ) {
            return 0;
        }

        $count = 0;
        $autoTrx = $this->getFlag( self::DBO_TRX ); // automatic begin() enabled?
        /** @var Throwable $e */
        $e = null; // first exception
        do { // callbacks may add callbacks :)
            $callbacks = array_merge(
                $this->trxIdleCallbacks,
                $this->trxEndCallbacks // include "transaction resolution" callbacks
            );
            $this->trxIdleCallbacks = []; // consumed (and recursion guard)
            $this->trxEndCallbacks = []; // consumed (recursion guard)

            // Only run trxSectionCancelCallbacks on rollback, not commit.
            // But always consume them.
            if ( $trigger === self::TRIGGER_ROLLBACK ) {
                $callbacks = array_merge( $callbacks, $this->trxSectionCancelCallbacks );
            }
            $this->trxSectionCancelCallbacks = []; // consumed (recursion guard)

            foreach ( $callbacks as $callback ) {
                ++$count;
                list( $phpCallback ) = $callback;
                $this->clearFlag( self::DBO_TRX ); // make each query its own transaction
                try {
                    call_user_func( $phpCallback, $trigger, $this );
                } catch ( Throwable $ex ) {
                    call_user_func( $this->errorLogger, $ex );
                    $e = $e ?: $ex;
                    // Some callbacks may use startAtomic/endAtomic, so make sure
                    // their transactions are ended so other callbacks don't fail
                    if ( $this->trxLevel() ) {
                        $this->rollback( __METHOD__, self::FLUSHING_INTERNAL );
                    }
                } finally {
                    if ( $autoTrx ) {
                        $this->setFlag( self::DBO_TRX ); // restore automatic begin()
                    } else {
                        $this->clearFlag( self::DBO_TRX ); // restore auto-commit
                    }
                }
            }
            // @phan-suppress-next-line PhanImpossibleConditionInLoop
        } while ( count( $this->trxIdleCallbacks ) );

        if ( $e instanceof Throwable ) {
            throw $e; // re-throw any first exception
        }

        return $count;
    }

    /**
     * Actually consume and run any "on transaction pre-commit" callbacks.
     *
     * This method should not be used outside of Database/LoadBalancer
     *
     * @since 1.22
     * @return int Number of callbacks attempted
     * @throws Exception
     */
    public function runOnTransactionPreCommitCallbacks() {
        $count = 0;

        $e = null; // first exception
        do { // callbacks may add callbacks :)
            $callbacks = $this->trxPreCommitCallbacks;
            $this->trxPreCommitCallbacks = []; // consumed (and recursion guard)
            foreach ( $callbacks as $callback ) {
                try {
                    ++$count;
                    list( $phpCallback ) = $callback;
                    // @phan-suppress-next-line PhanUndeclaredInvokeInCallable
                    $phpCallback( $this );
                } catch ( Throwable $ex ) {
                    ( $this->errorLogger )( $ex );
                    $e = $e ?: $ex;
                }
            }
            // @phan-suppress-next-line PhanImpossibleConditionInLoop
        } while ( count( $this->trxPreCommitCallbacks ) );

        if ( $e instanceof Throwable ) {
            throw $e; // re-throw any first exception
        }

        return $count;
    }

    /**
     * Actually run any "atomic section cancel" callbacks.
     *
     * @param int $trigger IDatabase::TRIGGER_* constant
     * @param AtomicSectionIdentifier[]|null $sectionIds Section IDs to cancel,
     *  null on transaction rollback
     */
    private function runOnAtomicSectionCancelCallbacks(
        $trigger, array $sectionIds = null
    ) {
        /** @var Throwable $e */
        $e = null; // first exception

        $notCancelled = [];
        do {
            $callbacks = $this->trxSectionCancelCallbacks;
            $this->trxSectionCancelCallbacks = []; // consumed (recursion guard)
            foreach ( $callbacks as $entry ) {
                if ( $sectionIds === null || in_array( $entry[2], $sectionIds, true ) ) {
                    try {
                        // @phan-suppress-next-line PhanUndeclaredInvokeInCallable
                        $entry[0]( $trigger, $this );
                    } catch ( Throwable $ex ) {
                        ( $this->errorLogger )( $ex );
                        $e = $e ?: $ex;
                    }
                } else {
                    $notCancelled[] = $entry;
                }
            }
            // @phan-suppress-next-line PhanImpossibleConditionInLoop
        } while ( count( $this->trxSectionCancelCallbacks ) );
        $this->trxSectionCancelCallbacks = $notCancelled;

        if ( $e !== null ) {
            throw $e; // re-throw any first Throwable
        }
    }

    /**
     * Actually run any "transaction listener" callbacks.
     *
     * This method should not be used outside of Database/LoadBalancer
     *
     * @param int $trigger IDatabase::TRIGGER_* constant
     * @throws Exception
     * @since 1.20
     */
    public function runTransactionListenerCallbacks( $trigger ) {
        if ( $this->trxEndCallbacksSuppressed ) {
            return;
        }

        /** @var Throwable $e */
        $e = null; // first exception

        foreach ( $this->trxRecurringCallbacks as $phpCallback ) {
            try {
                $phpCallback( $trigger, $this );
            } catch ( Throwable $ex ) {
                ( $this->errorLogger )( $ex );
                $e = $e ?: $ex;
            }
        }

        if ( $e instanceof Throwable ) {
            throw $e; // re-throw any first exception
        }
    }

    /**
     * Create a savepoint
     *
     * This is used internally to implement atomic sections. It should not be
     * used otherwise.
     *
     * @since 1.31
     * @param string $identifier Identifier for the savepoint
     * @param string $fname Calling function name
     */
    protected function doSavepoint( $identifier, $fname ) {
        $sql = 'SAVEPOINT ' . $this->addIdentifierQuotes( $identifier );
        $this->query( $sql, $fname, self::QUERY_CHANGE_TRX );
    }

    /**
     * Release a savepoint
     *
     * This is used internally to implement atomic sections. It should not be
     * used otherwise.
     *
     * @since 1.31
     * @param string $identifier Identifier for the savepoint
     * @param string $fname Calling function name
     */
    protected function doReleaseSavepoint( $identifier, $fname ) {
        $sql = 'RELEASE SAVEPOINT ' . $this->addIdentifierQuotes( $identifier );
        $this->query( $sql, $fname, self::QUERY_CHANGE_TRX );
    }

    /**
     * Rollback to a savepoint
     *
     * This is used internally to implement atomic sections. It should not be
     * used otherwise.
     *
     * @since 1.31
     * @param string $identifier Identifier for the savepoint
     * @param string $fname Calling function name
     */
    protected function doRollbackToSavepoint( $identifier, $fname ) {
        $sql = 'ROLLBACK TO SAVEPOINT ' . $this->addIdentifierQuotes( $identifier );
        $this->query( $sql, $fname, self::QUERY_CHANGE_TRX );
    }

    /**
     * @param string $fname
     * @return string
     */
    private function nextSavepointId( $fname ) {
        $savepointId = self::$SAVEPOINT_PREFIX . ++$this->trxAtomicCounter;
        if ( strlen( $savepointId ) > 30 ) {
            // 30 == Oracle's identifier length limit (pre 12c)
            // With a 22 character prefix, that puts the highest number at 99999999.
            throw new DBUnexpectedError(
                $this,
                'There have been an excessively large number of atomic sections in a transaction'
                . " started by $this->trxFname (at $fname)"
            );
        }

        return $savepointId;
    }

    final public function startAtomic(
        $fname = __METHOD__, $cancelable = self::ATOMIC_NOT_CANCELABLE
    ) {
        $savepointId = $cancelable === self::ATOMIC_CANCELABLE ? self::$NOT_APPLICABLE : null;

        if ( !$this->trxLevel() ) {
            $this->begin( $fname, self::TRANSACTION_INTERNAL ); // sets trxAutomatic
            // If DBO_TRX is set, a series of startAtomic/endAtomic pairs will result
            // in all changes being in one transaction to keep requests transactional.
            if ( $this->getFlag( self::DBO_TRX ) ) {
                // Since writes could happen in between the topmost atomic sections as part
                // of the transaction, those sections will need savepoints.
                $savepointId = $this->nextSavepointId( $fname );
                $this->doSavepoint( $savepointId, $fname );
            } else {
                $this->trxAutomaticAtomic = true;
            }
        } elseif ( $cancelable === self::ATOMIC_CANCELABLE ) {
            $savepointId = $this->nextSavepointId( $fname );
            $this->doSavepoint( $savepointId, $fname );
        }

        $sectionId = new AtomicSectionIdentifier;
        $this->trxAtomicLevels[] = [ $fname, $sectionId, $savepointId ];
        $this->queryLogger->debug( 'startAtomic: entering level ' .
            ( count( $this->trxAtomicLevels ) - 1 ) . " ($fname)" );

        return $sectionId;
    }

    final public function endAtomic( $fname = __METHOD__ ) {
        if ( !$this->trxLevel() || !$this->trxAtomicLevels ) {
            throw new DBUnexpectedError( $this, "No atomic section is open (got $fname)" );
        }

        // Check if the current section matches $fname
        $pos = count( $this->trxAtomicLevels ) - 1;
        list( $savedFname, $sectionId, $savepointId ) = $this->trxAtomicLevels[$pos];
        $this->queryLogger->debug( "endAtomic: leaving level $pos ($fname)" );

        if ( $savedFname !== $fname ) {
            throw new DBUnexpectedError(
                $this,
                "Invalid atomic section ended (got $fname but expected $savedFname)"
            );
        }

        // Remove the last section (no need to re-index the array)
        array_pop( $this->trxAtomicLevels );

        if ( !$this->trxAtomicLevels && $this->trxAutomaticAtomic ) {
            $this->commit( $fname, self::FLUSHING_INTERNAL );
        } elseif ( $savepointId !== null && $savepointId !== self::$NOT_APPLICABLE ) {
            $this->doReleaseSavepoint( $savepointId, $fname );
        }

        // Hoist callback ownership for callbacks in the section that just ended;
        // all callbacks should have an owner that is present in trxAtomicLevels.
        $currentSectionId = $this->currentAtomicSectionId();
        if ( $currentSectionId ) {
            $this->reassignCallbacksForSection( $sectionId, $currentSectionId );
        }
    }

    final public function cancelAtomic(
        $fname = __METHOD__, AtomicSectionIdentifier $sectionId = null
    ) {
        if ( !$this->trxLevel() || !$this->trxAtomicLevels ) {
            throw new DBUnexpectedError( $this, "No atomic section is open (got $fname)" );
        }

        $excisedIds = [];
        $newTopSection = $this->currentAtomicSectionId();
        try {
            $excisedFnames = [];
            if ( $sectionId !== null ) {
                // Find the (last) section with the given $sectionId
                $pos = -1;
                foreach ( $this->trxAtomicLevels as $i => list( $asFname, $asId, $spId ) ) {
                    if ( $asId === $sectionId ) {
                        $pos = $i;
                    }
                }
                if ( $pos < 0 ) {
                    throw new DBUnexpectedError( $this, "Atomic section not found (for $fname)" );
                }
                // Remove all descendant sections and re-index the array
                $len = count( $this->trxAtomicLevels );
                for ( $i = $pos + 1; $i < $len; ++$i ) {
                    $excisedFnames[] = $this->trxAtomicLevels[$i][0];
                    $excisedIds[] = $this->trxAtomicLevels[$i][1];
                }
                $this->trxAtomicLevels = array_slice( $this->trxAtomicLevels, 0, $pos + 1 );
                $newTopSection = $this->currentAtomicSectionId();
            }

            // Check if the current section matches $fname
            $pos = count( $this->trxAtomicLevels ) - 1;
            list( $savedFname, $savedSectionId, $savepointId ) = $this->trxAtomicLevels[$pos];

            if ( $excisedFnames ) {
                $this->queryLogger->debug( "cancelAtomic: canceling level $pos ($savedFname) " .
                    "and descendants " . implode( ', ', $excisedFnames ) );
            } else {
                $this->queryLogger->debug( "cancelAtomic: canceling level $pos ($savedFname)" );
            }

            if ( $savedFname !== $fname ) {
                throw new DBUnexpectedError(
                    $this,
                    "Invalid atomic section ended (got $fname but expected $savedFname)"
                );
            }

            // Remove the last section (no need to re-index the array)
            array_pop( $this->trxAtomicLevels );
            $excisedIds[] = $savedSectionId;
            $newTopSection = $this->currentAtomicSectionId();

            if ( $savepointId !== null ) {
                // Rollback the transaction to the state just before this atomic section
                if ( $savepointId === self::$NOT_APPLICABLE ) {
                    $this->rollback( $fname, self::FLUSHING_INTERNAL );
                    // Note: rollback() will run trxSectionCancelCallbacks
                } else {
                    $this->doRollbackToSavepoint( $savepointId, $fname );
                    $this->trxStatus = self::STATUS_TRX_OK; // no exception; recovered
                    $this->trxStatusIgnoredCause = null;

                    // Run trxSectionCancelCallbacks now.
                    $this->runOnAtomicSectionCancelCallbacks( self::TRIGGER_CANCEL, $excisedIds );
                }
            } elseif ( $this->trxStatus > self::STATUS_TRX_ERROR ) {
                // Put the transaction into an error state if it's not already in one
                $this->trxStatus = self::STATUS_TRX_ERROR;
                $this->trxStatusCause = new DBUnexpectedError(
                    $this,
                    "Uncancelable atomic section canceled (got $fname)"
                );
            }
        } finally {
            // Fix up callbacks owned by the sections that were just cancelled.
            // All callbacks should have an owner that is present in trxAtomicLevels.
            $this->modifyCallbacksForCancel( $excisedIds, $newTopSection );
        }

        $this->affectedRowCount = 0; // for the sake of consistency
    }

    final public function doAtomicSection(
        $fname, callable $callback, $cancelable = self::ATOMIC_NOT_CANCELABLE
    ) {
        $sectionId = $this->startAtomic( $fname, $cancelable );
        try {
            $res = $callback( $this, $fname );
        } catch ( Throwable $e ) {
            $this->cancelAtomic( $fname, $sectionId );

            throw $e;
        }
        $this->endAtomic( $fname );

        return $res;
    }

    final public function begin( $fname = __METHOD__, $mode = self::TRANSACTION_EXPLICIT ) {
        static $modes = [ self::TRANSACTION_EXPLICIT, self::TRANSACTION_INTERNAL ];
        if ( !in_array( $mode, $modes, true ) ) {
            throw new DBUnexpectedError( $this, "$fname: invalid mode parameter '$mode'" );
        }

        // Protect against mismatched atomic section, transaction nesting, and snapshot loss
        if ( $this->trxLevel() ) {
            if ( $this->trxAtomicLevels ) {
                $levels = $this->flatAtomicSectionList();
                $msg = "$fname: got explicit BEGIN while atomic section(s) $levels are open";
                throw new DBUnexpectedError( $this, $msg );
            } elseif ( !$this->trxAutomatic ) {
                $msg = "$fname: explicit transaction already active (from {$this->trxFname})";
                throw new DBUnexpectedError( $this, $msg );
            } else {
                $msg = "$fname: implicit transaction already active (from {$this->trxFname})";
                throw new DBUnexpectedError( $this, $msg );
            }
        } elseif ( $this->getFlag( self::DBO_TRX ) && $mode !== self::TRANSACTION_INTERNAL ) {
            $msg = "$fname: implicit transaction expected (DBO_TRX set)";
            throw new DBUnexpectedError( $this, $msg );
        }

        $this->assertHasConnectionHandle();

        $this->doBegin( $fname );
        $this->trxShortId = sprintf( '%06x', mt_rand( 0, 0xffffff ) );
        $this->trxStatus = self::STATUS_TRX_OK;
        $this->trxStatusIgnoredCause = null;
        $this->trxAtomicCounter = 0;
        $this->trxTimestamp = microtime( true );
        $this->trxFname = $fname;
        $this->trxDoneWrites = false;
        $this->trxAutomaticAtomic = false;
        $this->trxAtomicLevels = [];
        $this->trxWriteDuration = 0.0;
        $this->trxWriteQueryCount = 0;
        $this->trxWriteAffectedRows = 0;
        $this->trxWriteAdjDuration = 0.0;
        $this->trxWriteAdjQueryCount = 0;
        $this->trxWriteCallers = [];
        // First SELECT after BEGIN will establish the snapshot in REPEATABLE-READ.
        // Get an estimate of the replication lag before any such queries.
        $this->trxReplicaLag = null; // clear cached value first
        $this->trxReplicaLag = $this->getApproximateLagStatus()['lag'];
        // T147697: make explicitTrxActive() return true until begin() finishes. This way, no
        // caller will think its OK to muck around with the transaction just because startAtomic()
        // has not yet completed (e.g. setting trxAtomicLevels).
        $this->trxAutomatic = ( $mode === self::TRANSACTION_INTERNAL );
    }

    /**
     * Issues the BEGIN command to the database server.
     *
     * @see Database::begin()
     * @param string $fname
     * @throws DBError
     */
    protected function doBegin( $fname ) {
        $this->query( 'BEGIN', $fname, self::QUERY_CHANGE_TRX );
    }

    final public function commit( $fname = __METHOD__, $flush = self::FLUSHING_ONE ) {
        static $modes = [ self::FLUSHING_ONE, self::FLUSHING_ALL_PEERS, self::FLUSHING_INTERNAL ];
        if ( !in_array( $flush, $modes, true ) ) {
            throw new DBUnexpectedError( $this, "$fname: invalid flush parameter '$flush'" );
        }

        if ( $this->trxLevel() && $this->trxAtomicLevels ) {
            // There are still atomic sections open; this cannot be ignored
            $levels = $this->flatAtomicSectionList();
            throw new DBUnexpectedError(
                $this,
                "$fname: got COMMIT while atomic sections $levels are still open"
            );
        }

        if ( $flush === self::FLUSHING_INTERNAL || $flush === self::FLUSHING_ALL_PEERS ) {
            if ( !$this->trxLevel() ) {
                return; // nothing to do
            } elseif ( !$this->trxAutomatic ) {
                throw new DBUnexpectedError(
                    $this,
                    "$fname: flushing an explicit transaction, getting out of sync"
                );
            }
        } elseif ( !$this->trxLevel() ) {
            $this->queryLogger->error(
                "$fname: no transaction to commit, something got out of sync" );
            return; // nothing to do
        } elseif ( $this->trxAutomatic ) {
            throw new DBUnexpectedError(
                $this,
                "$fname: expected mass commit of all peer transactions (DBO_TRX set)"
            );
        }

        $this->assertHasConnectionHandle();

        $this->runOnTransactionPreCommitCallbacks();

        $writeTime = $this->pendingWriteQueryDuration( self::ESTIMATE_DB_APPLY );
        $this->doCommit( $fname );
        $oldTrxShortId = $this->consumeTrxShortId();
        $this->trxStatus = self::STATUS_TRX_NONE;

        if ( $this->trxDoneWrites ) {
            $this->lastWriteTime = microtime( true );
            $this->trxProfiler->transactionWritingOut(
                $this->server,
                $this->getDomainID(),
                $oldTrxShortId,
                $writeTime,
                $this->trxWriteAffectedRows
            );
        }

        // With FLUSHING_ALL_PEERS, callbacks will be explicitly run later
        if ( $flush !== self::FLUSHING_ALL_PEERS ) {
            $this->runOnTransactionIdleCallbacks( self::TRIGGER_COMMIT );
            $this->runTransactionListenerCallbacks( self::TRIGGER_COMMIT );
        }
    }

    /**
     * Issues the COMMIT command to the database server.
     *
     * @see Database::commit()
     * @param string $fname
     * @throws DBError
     */
    protected function doCommit( $fname ) {
        if ( $this->trxLevel() ) {
            $this->query( 'COMMIT', $fname, self::QUERY_CHANGE_TRX );
        }
    }

    final public function rollback( $fname = __METHOD__, $flush = self::FLUSHING_ONE ) {
        $trxActive = $this->trxLevel();

        if ( $flush !== self::FLUSHING_INTERNAL
            && $flush !== self::FLUSHING_ALL_PEERS
            && $this->getFlag( self::DBO_TRX )
        ) {
            throw new DBUnexpectedError(
                $this,
                "$fname: Expected mass rollback of all peer transactions (DBO_TRX set)"
            );
        }

        if ( $trxActive ) {
            $this->assertHasConnectionHandle();

            $this->doRollback( $fname );
            $oldTrxShortId = $this->consumeTrxShortId();
            $this->trxStatus = self::STATUS_TRX_NONE;
            $this->trxAtomicLevels = [];
            // Estimate the RTT via a query now that trxStatus is OK
            $writeTime = $this->pingAndCalculateLastTrxApplyTime();

            if ( $this->trxDoneWrites ) {
                $this->trxProfiler->transactionWritingOut(
                    $this->server,
                    $this->getDomainID(),
                    $oldTrxShortId,
                    $writeTime,
                    $this->trxWriteAffectedRows
                );
            }
        }

        // Clear any commit-dependant callbacks. They might even be present
        // only due to transaction rounds, with no SQL transaction being active
        $this->trxIdleCallbacks = [];
        $this->trxPreCommitCallbacks = [];

        // With FLUSHING_ALL_PEERS, callbacks will be explicitly run later
        if ( $trxActive && $flush !== self::FLUSHING_ALL_PEERS ) {
            try {
                $this->runOnTransactionIdleCallbacks( self::TRIGGER_ROLLBACK );
            } catch ( Throwable $e ) {
                // already logged; finish and let LoadBalancer move on during mass-rollback
            }
            try {
                $this->runTransactionListenerCallbacks( self::TRIGGER_ROLLBACK );
            } catch ( Throwable $e ) {
                // already logged; let LoadBalancer move on during mass-rollback
            }

            $this->affectedRowCount = 0; // for the sake of consistency
        }
    }

    /**
     * Issues the ROLLBACK command to the database server.
     *
     * @see Database::rollback()
     * @param string $fname
     * @throws DBError
     */
    protected function doRollback( $fname ) {
        if ( $this->trxLevel() ) {
            # Disconnects cause rollback anyway, so ignore those errors
            $this->query( 'ROLLBACK', $fname, self::QUERY_SILENCE_ERRORS | self::QUERY_CHANGE_TRX );
        }
    }

    public function flushSnapshot( $fname = __METHOD__, $flush = self::FLUSHING_ONE ) {
        if ( $this->explicitTrxActive() ) {
            // Committing this transaction would break callers that assume it is still open
            throw new DBUnexpectedError(
                $this,
                "$fname: Cannot flush snapshot; " .
                "explicit transaction '{$this->trxFname}' is still open"
            );
        } elseif ( $this->writesOrCallbacksPending() ) {
            // This only flushes transactions to clear snapshots, not to write data
            $fnames = implode( ', ', $this->pendingWriteAndCallbackCallers() );
            throw new DBUnexpectedError(
                $this,
                "$fname: Cannot flush snapshot; " .
                "writes from transaction {$this->trxFname} are still pending ($fnames)"
            );
        } elseif (
            $this->trxLevel() &&
            $this->getTransactionRoundId() &&
            $flush !== self::FLUSHING_INTERNAL &&
            $flush !== self::FLUSHING_ALL_PEERS
        ) {
            $this->queryLogger->warning(
                "$fname: Expected mass snapshot flush of all peer transactions " .
                "in the explicit transactions round '{$this->getTransactionRoundId()}'",
                [ 'exception' => new RuntimeException() ]
            );
        }

        $this->commit( $fname, self::FLUSHING_INTERNAL );
    }

    public function explicitTrxActive() {
        return $this->trxLevel() && ( $this->trxAtomicLevels || !$this->trxAutomatic );
    }

    public function duplicateTableStructure(
        $oldName, $newName, $temporary = false, $fname = __METHOD__
    ) {
        throw new RuntimeException( __METHOD__ . ' is not implemented in descendant class' );
    }

    public function listTables( $prefix = null, $fname = __METHOD__ ) {
        throw new RuntimeException( __METHOD__ . ' is not implemented in descendant class' );
    }

    public function listViews( $prefix = null, $fname = __METHOD__ ) {
        throw new RuntimeException( __METHOD__ . ' is not implemented in descendant class' );
    }

    public function timestamp( $ts = 0 ) {
        $t = new ConvertibleTimestamp( $ts );
        // Let errors bubble up to avoid putting garbage in the DB
        return $t->getTimestamp( TS_MW );
    }

    public function timestampOrNull( $ts = null ) {
        if ( $ts === null ) {
            return null;
        } else {
            return $this->timestamp( $ts );
        }
    }

    public function affectedRows() {
        return ( $this->affectedRowCount === null )
            ? $this->fetchAffectedRowCount() // default to driver value
            : $this->affectedRowCount;
    }

    /**
     * @return int Number of retrieved rows according to the driver
     */
    abstract protected function fetchAffectedRowCount();

    /**
     * Take a query result and wrap it in an iterable result wrapper if necessary.
     * Booleans are passed through as-is to indicate success/failure of write queries.
     *
     * Once upon a time, Database::query() returned a bare MySQL result
     * resource, and it was necessary to call this function to convert it to
     * a wrapper. Nowadays, raw database objects are never exposed to external
     * callers, so this is unnecessary in external code.
     *
     * @param bool|IResultWrapper|resource $result
     * @return bool|IResultWrapper
     */
    protected function resultObject( $result ) {
        if ( !$result ) {
            return false; // failed query
        } elseif ( $result instanceof IResultWrapper ) {
            return $result;
        } elseif ( $result === true ) {
            return $result; // successful write query
        } else {
            return new ResultWrapper( $this, $result );
        }
    }

    public function ping( &$rtt = null ) {
        // Avoid hitting the server if it was hit recently
        if ( $this->isOpen() && ( microtime( true ) - $this->lastPing ) < self::$PING_TTL ) {
            if ( !func_num_args() || $this->lastRoundTripEstimate > 0 ) {
                $rtt = $this->lastRoundTripEstimate;
                return true; // don't care about $rtt
            }
        }

        // This will reconnect if possible or return false if not
        $flags = self::QUERY_IGNORE_DBO_TRX | self::QUERY_SILENCE_ERRORS | self::QUERY_CHANGE_NONE;
        $ok = ( $this->query( self::$PING_QUERY, __METHOD__, $flags ) !== false );
        if ( $ok ) {
            $rtt = $this->lastRoundTripEstimate;
        }

        return $ok;
    }

    /**
     * Close any existing (dead) database connection and open a new connection
     *
     * @param string $fname
     * @return bool True if new connection is opened successfully, false if error
     */
    protected function replaceLostConnection( $fname ) {
        $this->closeConnection();
        $this->conn = null;

        $this->handleSessionLossPreconnect();

        try {
            $this->open(
                $this->server,
                $this->user,
                $this->password,
                $this->currentDomain->getDatabase(),
                $this->currentDomain->getSchema(),
                $this->tablePrefix()
            );
            $this->lastPing = microtime( true );
            $ok = true;

            $this->connLogger->warning(
                $fname . ': lost connection to {dbserver}; reconnected',
                [
                    'dbserver' => $this->getServer(),
                    'exception' => new RuntimeException()
                ]
            );
        } catch ( DBConnectionError $e ) {
            $ok = false;

            $this->connLogger->error(
                $fname . ': lost connection to {dbserver} permanently',
                [ 'dbserver' => $this->getServer() ]
            );
        }

        $this->handleSessionLossPostconnect();

        return $ok;
    }

    public function getSessionLagStatus() {
        return $this->getRecordedTransactionLagStatus() ?: $this->getApproximateLagStatus();
    }

    /**
     * Get the replica DB lag when the current transaction started
     *
     * This is useful when transactions might use snapshot isolation
     * (e.g. REPEATABLE-READ in innodb), so the "real" lag of that data
     * is this lag plus transaction duration. If they don't, it is still
     * safe to be pessimistic. This returns null if there is no transaction.
     *
     * This returns null if the lag status for this transaction was not yet recorded.
     *
     * @return array|null ('lag': seconds or false on error, 'since': UNIX timestamp of BEGIN)
     * @since 1.27
     */
    final protected function getRecordedTransactionLagStatus() {
        return ( $this->trxLevel() && $this->trxReplicaLag !== null )
            ? [ 'lag' => $this->trxReplicaLag, 'since' => $this->trxTimestamp() ]
            : null;
    }

    /**
     * Get a replica DB lag estimate for this server at the start of a transaction
     *
     * This is a no-op unless the server is known a priori to be a replica DB
     *
     * @return array ('lag': seconds or false on error, 'since': UNIX timestamp of estimate)
     * @since 1.27
     */
    protected function getApproximateLagStatus() {
        return [
            'lag' => ( $this->topologyRole === self::ROLE_STREAMING_REPLICA ) ? $this->getLag() : 0,
            'since' => microtime( true )
        ];
    }

    /**
     * Merge the result of getSessionLagStatus() for several DBs
     * using the most pessimistic values to estimate the lag of
     * any data derived from them in combination
     *
     * This is information is useful for caching modules
     *
     * @see WANObjectCache::set()
     * @see WANObjectCache::getWithSetCallback()
     *
     * @param IDatabase $db1
     * @param IDatabase|null $db2 [optional]
     * @return array Map of values:
     *   - lag: highest lag of any of the DBs or false on error (e.g. replication stopped)
     *   - since: oldest UNIX timestamp of any of the DB lag estimates
     *   - pending: whether any of the DBs have uncommitted changes
     * @throws DBError
     * @since 1.27
     */
    public static function getCacheSetOptions( IDatabase $db1, IDatabase $db2 = null ) {
        $res = [ 'lag' => 0, 'since' => INF, 'pending' => false ];
        foreach ( func_get_args() as $db ) {
            /** @var IDatabase $db */
            $status = $db->getSessionLagStatus();
            if ( $status['lag'] === false ) {
                $res['lag'] = false;
            } elseif ( $res['lag'] !== false ) {
                $res['lag'] = max( $res['lag'], $status['lag'] );
            }
            $res['since'] = min( $res['since'], $status['since'] );
            $res['pending'] = $res['pending'] ?: $db->writesPending();
        }

        return $res;
    }

    public function getLag() {
        if ( $this->topologyRole === self::ROLE_STREAMING_MASTER ) {
            return 0; // this is the master
        } elseif ( $this->topologyRole === self::ROLE_STATIC_CLONE ) {
            return 0; // static dataset
        }

        return $this->doGetLag();
    }

    protected function doGetLag() {
        return 0;
    }

    public function maxListLen() {
        return 0;
    }

    public function encodeBlob( $b ) {
        return $b;
    }

    public function decodeBlob( $b ) {
        if ( $b instanceof Blob ) {
            $b = $b->fetch();
        }
        return $b;
    }

    public function setSessionOptions( array $options ) {
    }

    public function sourceFile(
        $filename,
        callable $lineCallback = null,
        callable $resultCallback = null,
        $fname = false,
        callable $inputCallback = null
    ) {
        AtEase::suppressWarnings();
        $fp = fopen( $filename, 'r' );
        AtEase::restoreWarnings();

        if ( $fp === false ) {
            throw new RuntimeException( "Could not open \"{$filename}\"" );
        }

        if ( !$fname ) {
            $fname = __METHOD__ . "( $filename )";
        }

        try {
            $error = $this->sourceStream(
                $fp, $lineCallback, $resultCallback, $fname, $inputCallback );
        } catch ( Throwable $e ) {
            fclose( $fp );
            throw $e;
        }

        fclose( $fp );

        return $error;
    }

    public function setSchemaVars( $vars ) {
        $this->schemaVars = is_array( $vars ) ? $vars : null;
    }

    public function sourceStream(
        $fp,
        callable $lineCallback = null,
        callable $resultCallback = null,
        $fname = __METHOD__,
        callable $inputCallback = null
    ) {
        $delimiterReset = new ScopedCallback(
            function ( $delimiter ) {
                $this->delimiter = $delimiter;
            },
            [ $this->delimiter ]
        );
        $cmd = '';

        while ( !feof( $fp ) ) {
            if ( $lineCallback ) {
                call_user_func( $lineCallback );
            }

            $line = trim( fgets( $fp ) );

            if ( $line == '' ) {
                continue;
            }

            if ( $line[0] == '-' && $line[1] == '-' ) {
                continue;
            }

            if ( $cmd != '' ) {
                $cmd .= ' ';
            }

            $done = $this->streamStatementEnd( $cmd, $line );

            $cmd .= "$line\n";

            if ( $done || feof( $fp ) ) {
                $cmd = $this->replaceVars( $cmd );

                if ( $inputCallback ) {
                    $callbackResult = $inputCallback( $cmd );

                    if ( is_string( $callbackResult ) || !$callbackResult ) {
                        $cmd = $callbackResult;
                    }
                }

                if ( $cmd ) {
                    $res = $this->query( $cmd, $fname );

                    if ( $resultCallback ) {
                        $resultCallback( $res, $this );
                    }

                    if ( $res === false ) {
                        $err = $this->lastError();

                        return "Query \"{$cmd}\" failed with error code \"$err\".\n";
                    }
                }
                $cmd = '';
            }
        }

        ScopedCallback::consume( $delimiterReset );
        return true;
    }

    /**
     * Called by sourceStream() to check if we've reached a statement end
     *
     * @param string &$sql SQL assembled so far
     * @param string &$newLine New line about to be added to $sql
     * @return bool Whether $newLine contains end of the statement
     */
    public function streamStatementEnd( &$sql, &$newLine ) {
        if ( $this->delimiter ) {
            $prev = $newLine;
            $newLine = preg_replace(
                '/' . preg_quote( $this->delimiter, '/' ) . '$/', '', $newLine );
            if ( $newLine != $prev ) {
                return true;
            }
        }

        return false;
    }

    /**
     * Database independent variable replacement. Replaces a set of variables
     * in an SQL statement with their contents as given by $this->getSchemaVars().
     *
     * Supports '{$var}' `{$var}` and / *$var* / (without the spaces) style variables.
     *
     * - '{$var}' should be used for text and is passed through the database's
     *   addQuotes method.
     * - `{$var}` should be used for identifiers (e.g. table and database names).
     *   It is passed through the database's addIdentifierQuotes method which
     *   can be overridden if the database uses something other than backticks.
     * - / *_* / or / *$wgDBprefix* / passes the name that follows through the
     *   database's tableName method.
     * - / *i* / passes the name that follows through the database's indexName method.
     * - In all other cases, / *$var* / is left unencoded. Except for table options,
     *   its use should be avoided. In 1.24 and older, string encoding was applied.
     *
     * @param string $ins SQL statement to replace variables in
     * @return string The new SQL statement with variables replaced
     */
    protected function replaceVars( $ins ) {
        $vars = $this->getSchemaVars();
        return preg_replace_callback(
            '!
                /\* (\$wgDBprefix|[_i]) \*/ (\w*) | # 1-2. tableName, indexName
                \'\{\$ (\w+) }\'                  | # 3. addQuotes
                `\{\$ (\w+) }`                    | # 4. addIdentifierQuotes
                /\*\$ (\w+) \*/                     # 5. leave unencoded
            !x',
            function ( $m ) use ( $vars ) {
                // Note: Because of <https://bugs.php.net/bug.php?id=51881>,
                // check for both nonexistent keys *and* the empty string.
                if ( isset( $m[1] ) && $m[1] !== '' ) {
                    if ( $m[1] === 'i' ) {
                        return $this->indexName( $m[2] );
                    } else {
                        return $this->tableName( $m[2] );
                    }
                } elseif ( isset( $m[3] ) && $m[3] !== '' && array_key_exists( $m[3], $vars ) ) {
                    return $this->addQuotes( $vars[$m[3]] );
                } elseif ( isset( $m[4] ) && $m[4] !== '' && array_key_exists( $m[4], $vars ) ) {
                    return $this->addIdentifierQuotes( $vars[$m[4]] );
                } elseif ( isset( $m[5] ) && $m[5] !== '' && array_key_exists( $m[5], $vars ) ) {
                    return $vars[$m[5]];
                } else {
                    return $m[0];
                }
            },
            $ins
        );
    }

    /**
     * Get schema variables. If none have been set via setSchemaVars(), then
     * use some defaults from the current object.
     *
     * @return array
     */
    protected function getSchemaVars() {
        return $this->schemaVars ?? $this->getDefaultSchemaVars();
    }

    /**
     * Get schema variables to use if none have been set via setSchemaVars().
     *
     * Override this in derived classes to provide variables for tables.sql
     * and SQL patch files.
     *
     * @return array
     */
    protected function getDefaultSchemaVars() {
        return [];
    }

    public function lockIsFree( $lockName, $method ) {
        // RDBMs methods for checking named locks may or may not count this thread itself.
        // In MySQL, IS_FREE_LOCK() returns 0 if the thread already has the lock. This is
        // the behavior chosen by the interface for this method.
        return !isset( $this->sessionNamedLocks[$lockName] );
    }

    public function lock( $lockName, $method, $timeout = 5 ) {
        $this->sessionNamedLocks[$lockName] = 1;

        return true;
    }

    public function unlock( $lockName, $method ) {
        unset( $this->sessionNamedLocks[$lockName] );

        return true;
    }

    public function getScopedLockAndFlush( $lockKey, $fname, $timeout ) {
        if ( $this->writesOrCallbacksPending() ) {
            // This only flushes transactions to clear snapshots, not to write data
            $fnames = implode( ', ', $this->pendingWriteAndCallbackCallers() );
            throw new DBUnexpectedError(
                $this,
                "$fname: Cannot flush pre-lock snapshot; " .
                "writes from transaction {$this->trxFname} are still pending ($fnames)"
            );
        }

        if ( !$this->lock( $lockKey, $fname, $timeout ) ) {
            return null;
        }

        $unlocker = new ScopedCallback( function () use ( $lockKey, $fname ) {
            if ( $this->trxLevel() ) {
                // There is a good chance an exception was thrown, causing any early return
                // from the caller. Let any error handler get a chance to issue rollback().
                // If there isn't one, let the error bubble up and trigger server-side rollback.
                $this->onTransactionResolution(
                    function () use ( $lockKey, $fname ) {
                        $this->unlock( $lockKey, $fname );
                    },
                    $fname
                );
            } else {
                $this->unlock( $lockKey, $fname );
            }
        } );

        $this->commit( $fname, self::FLUSHING_INTERNAL );

        return $unlocker;
    }

    public function namedLocksEnqueue() {
        return false;
    }

    public function tableLocksHaveTransactionScope() {
        return true;
    }

    final public function lockTables( array $read, array $write, $method ) {
        if ( $this->writesOrCallbacksPending() ) {
            throw new DBUnexpectedError( $this, "Transaction writes or callbacks still pending" );
        }

        if ( $this->tableLocksHaveTransactionScope() ) {
            $this->startAtomic( $method );
        }

        return $this->doLockTables( $read, $write, $method );
    }

    /**
     * Helper function for lockTables() that handles the actual table locking
     *
     * @param array $read Array of tables to lock for read access
     * @param array $write Array of tables to lock for write access
     * @param string $method Name of caller
     * @return true
     */
    protected function doLockTables( array $read, array $write, $method ) {
        return true;
    }

    final public function unlockTables( $method ) {
        if ( $this->tableLocksHaveTransactionScope() ) {
            $this->endAtomic( $method );

            return true; // locks released on COMMIT/ROLLBACK
        }

        return $this->doUnlockTables( $method );
    }

    /**
     * Helper function for unlockTables() that handles the actual table unlocking
     *
     * @param string $method Name of caller
     * @return true
     */
    protected function doUnlockTables( $method ) {
        return true;
    }

    public function dropTable( $table, $fname = __METHOD__ ) {
        if ( !$this->tableExists( $table, $fname ) ) {
            return false;
        }

        $this->doDropTable( $table, $fname );

        return true;
    }

    /**
     * @see Database::dropTable()
     * @param string $table
     * @param string $fname
     */
    protected function doDropTable( $table, $fname ) {
        // https://mariadb.com/kb/en/drop-table/
        // https://dev.mysql.com/doc/refman/8.0/en/drop-table.html
        // https://www.postgresql.org/docs/9.2/sql-truncate.html
        $sql = "DROP TABLE " . $this->tableName( $table ) . " CASCADE";
        $this->query( $sql, $fname, self::QUERY_IGNORE_DBO_TRX );
    }

    public function truncate( $tables, $fname = __METHOD__ ) {
        $tables = is_array( $tables ) ? $tables : [ $tables ];

        $tablesTruncate = [];
        foreach ( $tables as $table ) {
            // Skip TEMPORARY tables with no writes nor sequence updates detected.
            // This mostly is an optimization for integration testing.
            if ( !$this->isPristineTemporaryTable( $table ) ) {
                $tablesTruncate[] = $table;
            }
        }

        if ( $tablesTruncate ) {
            $this->doTruncate( $tablesTruncate, $fname );
        }
    }

    /**
     * @see Database::truncate()
     * @param string[] $tables
     * @param string $fname
     */
    protected function doTruncate( array $tables, $fname ) {
        foreach ( $tables as $table ) {
            $sql = "TRUNCATE TABLE " . $this->tableName( $table );
            $this->query( $sql, $fname, self::QUERY_CHANGE_SCHEMA );
        }
    }

    public function getInfinity() {
        return 'infinity';
    }

    public function encodeExpiry( $expiry ) {
        return ( $expiry == '' || $expiry == 'infinity' || $expiry == $this->getInfinity() )
            ? $this->getInfinity()
            : $this->timestamp( $expiry );
    }

    public function decodeExpiry( $expiry, $format = TS_MW ) {
        if ( $expiry == '' || $expiry == 'infinity' || $expiry == $this->getInfinity() ) {
            return 'infinity';
        }

        return ConvertibleTimestamp::convert( $format, $expiry );
    }

    public function setBigSelects( $value = true ) {
        // no-op
    }

    public function isReadOnly() {
        return ( $this->getReadOnlyReason() !== false );
    }

    /**
     * @return array|bool Tuple of (read-only reason, "role" or "lb") or false if it is not
     */
    protected function getReadOnlyReason() {
        if ( $this->topologyRole === self::ROLE_STREAMING_REPLICA ) {
            return [ 'Server is configured as a read-only replica database.', 'role' ];
        } elseif ( $this->topologyRole === self::ROLE_STATIC_CLONE ) {
            return [ 'Server is configured as a read-only static clone database.', 'role' ];
        }

        $reason = $this->getLBInfo( self::LB_READ_ONLY_REASON );
        if ( is_string( $reason ) ) {
            return [ $reason, 'lb' ];
        }

        return false;
    }

    public function setTableAliases( array $aliases ) {
        $this->tableAliases = $aliases;
    }

    public function setIndexAliases( array $aliases ) {
        $this->indexAliases = $aliases;
    }

    /**
     * @param int $field
     * @param int $flags
     * @return bool
     * @since 1.34
     */
    final protected function fieldHasBit( $field, $flags ) {
        return ( ( $field & $flags ) === $flags );
    }

    /**
     * Get the underlying binding connection handle
     *
     * Makes sure the connection resource is set (disconnects and ping() failure can unset it).
     * This catches broken callers than catch and ignore disconnection exceptions.
     * Unlike checking isOpen(), this is safe to call inside of open().
     *
     * @return mixed
     * @throws DBUnexpectedError
     * @since 1.26
     */
    protected function getBindingHandle() {
        if ( !$this->conn ) {
            throw new DBUnexpectedError(
                $this,
                'DB connection was already closed or the connection dropped'
            );
        }

        return $this->conn;
    }

    public function __toString() {
        // spl_object_id is PHP >= 7.2
        $id = function_exists( 'spl_object_id' )
            ? spl_object_id( $this )
            : spl_object_hash( $this );

        $description = $this->getType() . ' object #' . $id;
        if ( is_resource( $this->conn ) ) {
            $description .= ' (' . (string)$this->conn . ')'; // "resource id #<ID>"
        } elseif ( is_object( $this->conn ) ) {
            // spl_object_id is PHP >= 7.2
            $handleId = function_exists( 'spl_object_id' )
                ? spl_object_id( $this->conn )
                : spl_object_hash( $this->conn );
            $description .= " (handle id #$handleId)";
        }

        return $description;
    }

    /**
     * Make sure that copies do not share the same client binding handle
     * @throws DBConnectionError
     */
    public function __clone() {
        $this->connLogger->warning(
            "Cloning " . static::class . " is not recommended; forking connection",
            [ 'exception' => new RuntimeException() ]
        );

        if ( $this->isOpen() ) {
            // Open a new connection resource without messing with the old one
            $this->conn = null;
            $this->trxEndCallbacks = []; // don't copy
            $this->trxSectionCancelCallbacks = []; // don't copy
            $this->handleSessionLossPreconnect(); // no trx or locks anymore
            $this->open(
                $this->server,
                $this->user,
                $this->password,
                $this->currentDomain->getDatabase(),
                $this->currentDomain->getSchema(),
                $this->tablePrefix()
            );
            $this->lastPing = microtime( true );
        }
    }

    /**
     * Called by serialize. Throw an exception when DB connection is serialized.
     * This causes problems on some database engines because the connection is
     * not restored on unserialize.
     */
    public function __sleep() {
        throw new RuntimeException( 'Database serialization may cause problems, since ' .
            'the connection is not restored on wakeup' );
    }

    /**
     * Run a few simple sanity checks and close dangling connections
     */
    public function __destruct() {
        if ( $this->trxLevel() && $this->trxDoneWrites ) {
            trigger_error( "Uncommitted DB writes (transaction from {$this->trxFname})" );
        }

        $danglingWriters = $this->pendingWriteAndCallbackCallers();
        if ( $danglingWriters ) {
            $fnames = implode( ', ', $danglingWriters );
            trigger_error( "DB transaction writes or callbacks still pending ($fnames)" );
        }

        if ( $this->conn ) {
            // Avoid connection leaks for sanity. Normally, resources close at script completion.
            // The connection might already be closed in PHP by now, so suppress warnings.
            AtEase::suppressWarnings();
            $this->closeConnection();
            AtEase::restoreWarnings();
            $this->conn = null;
        }
    }
}

/**
 * @deprecated since 1.28
 */
class_alias( Database::class, 'DatabaseBase' );

/**
 * @deprecated since 1.29
 */
class_alias( Database::class, 'Database' );