includes/libs/rdbms/loadbalancer/LoadBalancer.php
<?php
/**
* 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
*/
namespace Wikimedia\Rdbms;
use ArrayUtils;
use BagOStuff;
use EmptyBagOStuff;
use InvalidArgumentException;
use Liuggio\StatsdClient\Factory\StatsdDataFactoryInterface;
use LogicException;
use NullStatsdDataFactory;
use Psr\Log\LoggerInterface;
use Psr\Log\NullLogger;
use RuntimeException;
use Throwable;
use UnexpectedValueException;
use WANObjectCache;
use Wikimedia\ScopedCallback;
/**
* @see ILoadBalancer
* @ingroup Database
*/
class LoadBalancer implements ILoadBalancerForOwner {
/** @var ILoadMonitor */
private $loadMonitor;
/** @var BagOStuff */
private $srvCache;
/** @var WANObjectCache */
private $wanCache;
/** @var DatabaseFactory */
private $databaseFactory;
/** @var TransactionProfiler */
private $trxProfiler;
/** @var StatsdDataFactoryInterface */
private $statsd;
/** @var LoggerInterface */
private $logger;
/** @var callable Exception logger */
private $errorLogger;
/** @var DatabaseDomain Local DB domain ID and default for new connections */
private $localDomain;
/** @var array<string,array<int,Database[]>> Map of (connection pool => server index => Database[]) */
private $conns;
/** @var string|null The name of the DB cluster */
private $clusterName;
/** @var ServerInfo */
private $serverInfo;
/** @var array[] Map of (group => server index => weight) */
private $groupLoads;
/** @var string|null Default query group to use with getConnection() */
private $defaultGroup;
/** @var array[] $aliases Map of (table => (dbname, schema, prefix) map) */
private $tableAliases = [];
/** @var string[] Map of (index alias => index) */
private $indexAliases = [];
/** @var DatabaseDomain[]|string[] Map of (domain alias => DB domain) */
private $domainAliases = [];
/** @var callable[] Map of (name => callable) */
private $trxRecurringCallbacks = [];
/** @var bool[] Map of (domain => whether to use "temp tables only" mode) */
private $tempTablesOnlyMode = [];
/** @var string|false Explicit DBO_TRX transaction round active or false if none */
private $trxRoundId = false;
/** @var string Stage of the current transaction round in the transaction round life-cycle */
private $trxRoundStage = self::ROUND_CURSORY;
/** @var int[] The group replica server indexes keyed by group */
private $readIndexByGroup = [];
/** @var DBPrimaryPos|null Replication sync position or false if not set */
private $waitForPos;
/** @var bool Whether a lagged replica DB was used */
private $laggedReplicaMode = false;
/** @var string|false Reason this instance is read-only or false if not */
private $readOnlyReason = false;
/** @var int Total number of new connections ever made with this instance */
private $connectionCounter = 0;
/** @var bool */
private $disabled = false;
private ?ChronologyProtector $chronologyProtector = null;
/** @var bool Whether the session consistency callback already executed */
private $chronologyProtectorCalled = false;
/** @var Database|null The last connection handle that caused a problem */
private $lastErrorConn;
/** @var DatabaseDomain[] Map of (domain ID => domain instance) */
private $nonLocalDomainCache = [];
/**
* @var int Modification counter for invalidating connections held by
* DBConnRef instances. This is bumped by reconfigure().
*/
private $modcount = 0;
/** The "server index" LB info key; see {@link IDatabase::getLBInfo()} */
private const INFO_SERVER_INDEX = 'serverIndex';
/** The "connection category" LB info key; see {@link IDatabase::getLBInfo()} */
private const INFO_CONN_CATEGORY = 'connCategory';
/**
* Default 'maxLag' when unspecified
* @internal Only for use within LoadBalancer/LoadMonitor
*/
public const MAX_LAG_DEFAULT = ServerInfo::MAX_LAG_DEFAULT;
/** Warn when this many connection are held */
private const CONN_HELD_WARN_THRESHOLD = 10;
/** Default 'waitTimeout' when unspecified */
private const MAX_WAIT_DEFAULT = 10;
/** Seconds to cache primary DB server read-only status */
private const TTL_CACHE_READONLY = 5;
/** A category of connections that are tracked and transaction round aware */
private const CATEGORY_ROUND = 'round';
/** A category of connections that are tracked and in autocommit-mode */
private const CATEGORY_AUTOCOMMIT = 'auto-commit';
/** A category of connections that are untracked and in gauge-mode */
private const CATEGORY_GAUGE = 'gauge';
/** Transaction round, explicit or implicit, has not finished writing */
private const ROUND_CURSORY = 'cursory';
/** Transaction round writes are complete and ready for pre-commit checks */
private const ROUND_FINALIZED = 'finalized';
/** Transaction round passed final pre-commit checks */
private const ROUND_APPROVED = 'approved';
/** Transaction round was committed and post-commit callbacks must be run */
private const ROUND_COMMIT_CALLBACKS = 'commit-callbacks';
/** Transaction round was rolled back and post-rollback callbacks must be run */
private const ROUND_ROLLBACK_CALLBACKS = 'rollback-callbacks';
/** Transaction round encountered an error */
private const ROUND_ERROR = 'error';
/** @var int Idiom for getExistingReaderIndex() meaning "no index selected" */
private const READER_INDEX_NONE = -1;
public function __construct( array $params ) {
$this->configure( $params );
$this->conns = self::newTrackedConnectionsArray();
}
/**
* @param array $params A database configuration array, see $wgLBFactoryConf.
*
* @return void
*/
protected function configure( array $params ): void {
$this->localDomain = isset( $params['localDomain'] )
? DatabaseDomain::newFromId( $params['localDomain'] )
: DatabaseDomain::newUnspecified();
$this->serverInfo = new ServerInfo();
$this->groupLoads = [ self::GROUP_GENERIC => [] ];
foreach ( $this->serverInfo->normalizeServerMaps( $params['servers'] ?? [] ) as $i => $server ) {
$this->serverInfo->addServer( $i, $server );
foreach ( $server['groupLoads'] as $group => $weight ) {
$this->groupLoads[$group][$i] = $weight;
}
$this->groupLoads[self::GROUP_GENERIC][$i] = $server['load'];
}
if ( isset( $params['readOnlyReason'] ) && is_string( $params['readOnlyReason'] ) ) {
$this->readOnlyReason = $params['readOnlyReason'];
}
$this->srvCache = $params['srvCache'] ?? new EmptyBagOStuff();
$this->wanCache = $params['wanCache'] ?? WANObjectCache::newEmpty();
// Note: this parameter is normally absent. It is injectable for testing purposes only.
$this->databaseFactory = $params['databaseFactory'] ?? new DatabaseFactory( $params );
$this->errorLogger = $params['errorLogger'] ?? static function ( Throwable $e ) {
trigger_error( get_class( $e ) . ': ' . $e->getMessage(), E_USER_WARNING );
};
$this->logger = $params['logger'] ?? new NullLogger();
$this->clusterName = $params['clusterName'] ?? null;
$this->trxProfiler = $params['trxProfiler'] ?? new TransactionProfiler();
$this->statsd = $params['statsdDataFactory'] ?? new NullStatsdDataFactory();
// Set up LoadMonitor
$loadMonitorConfig = $params['loadMonitor'] ?? [ 'class' => 'LoadMonitorNull' ];
$loadMonitorConfig += [ 'lagWarnThreshold' => self::MAX_LAG_DEFAULT ];
$compat = [
'LoadMonitor' => LoadMonitor::class,
'LoadMonitorNull' => LoadMonitorNull::class
];
$class = $loadMonitorConfig['class'];
if ( isset( $compat[$class] ) ) {
$class = $compat[$class];
}
$this->loadMonitor = new $class(
$this, $this->srvCache, $this->wanCache, $loadMonitorConfig );
$this->loadMonitor->setLogger( $this->logger );
$this->loadMonitor->setStatsdDataFactory( $this->statsd );
if ( isset( $params['chronologyProtector'] ) ) {
$this->chronologyProtector = $params['chronologyProtector'];
}
if ( isset( $params['roundStage'] ) ) {
if ( $params['roundStage'] === self::STAGE_POSTCOMMIT_CALLBACKS ) {
$this->trxRoundStage = self::ROUND_COMMIT_CALLBACKS;
} elseif ( $params['roundStage'] === self::STAGE_POSTROLLBACK_CALLBACKS ) {
$this->trxRoundStage = self::ROUND_ROLLBACK_CALLBACKS;
}
}
$group = $params['defaultGroup'] ?? self::GROUP_GENERIC;
$this->defaultGroup = isset( $this->groupLoads[ $group ] ) ? $group : self::GROUP_GENERIC;
}
private static function newTrackedConnectionsArray() {
// Note that CATEGORY_GAUGE connections are untracked
return [
self::CATEGORY_ROUND => [],
self::CATEGORY_AUTOCOMMIT => []
];
}
public function getClusterName(): string {
// Fallback to the current primary name if not specified
return $this->clusterName ?? $this->getServerName( ServerInfo::WRITER_INDEX );
}
public function getLocalDomainID(): string {
return $this->localDomain->getId();
}
public function resolveDomainID( $domain ): string {
return $this->resolveDomainInstance( $domain )->getId();
}
/**
* @param DatabaseDomain|string|false $domain
* @return DatabaseDomain
*/
final protected function resolveDomainInstance( $domain ): DatabaseDomain {
if ( $domain instanceof DatabaseDomain ) {
return $domain; // already a domain instance
} elseif ( $domain === false || $domain === $this->localDomain->getId() ) {
return $this->localDomain;
} elseif ( isset( $this->domainAliases[$domain] ) ) {
$this->domainAliases[$domain] =
DatabaseDomain::newFromId( $this->domainAliases[$domain] );
return $this->domainAliases[$domain];
}
$cachedDomain = $this->nonLocalDomainCache[$domain] ?? null;
if ( $cachedDomain === null ) {
$cachedDomain = DatabaseDomain::newFromId( $domain );
$this->nonLocalDomainCache = [ $domain => $cachedDomain ];
}
return $cachedDomain;
}
/**
* Get the first group in $groups with assigned servers, falling back to the default group
*
* @param string[]|string|false $groups Query group(s) in preference order, [], or false
* @param int $i Specific server index or DB_PRIMARY/DB_REPLICA
* @return string Query group
*/
private function resolveGroups( $groups, $i ) {
// If a specific replica server was specified, then $groups makes no sense
if ( $i > 0 && $groups !== [] && $groups !== false ) {
$list = implode( ', ', (array)$groups );
throw new LogicException( "Query group(s) ($list) given with server index (#$i)" );
}
if ( $groups === [] || $groups === false || $groups === $this->defaultGroup ) {
$resolvedGroup = $this->defaultGroup;
} elseif ( is_string( $groups ) ) {
$resolvedGroup = isset( $this->groupLoads[$groups] ) ? $groups : $this->defaultGroup;
} elseif ( is_array( $groups ) ) {
$resolvedGroup = $this->defaultGroup;
foreach ( $groups as $group ) {
if ( isset( $this->groupLoads[$group] ) ) {
$resolvedGroup = $group;
break;
}
}
} else {
$resolvedGroup = $this->defaultGroup;
}
return $resolvedGroup;
}
/**
* Sanitize connection flags provided by a call to getConnection()
*
* @param int $flags Bitfield of class CONN_* constants
* @param int $i Specific server index or DB_PRIMARY/DB_REPLICA
* @param string $domain Database domain
* @return int Sanitized bitfield
*/
private function sanitizeConnectionFlags( $flags, $i, $domain ) {
// Whether an outside caller is explicitly requesting the primary database server
if ( $i === self::DB_PRIMARY || $i === ServerInfo::WRITER_INDEX ) {
$flags |= self::CONN_INTENT_WRITABLE;
}
if ( self::fieldHasBit( $flags, self::CONN_TRX_AUTOCOMMIT ) ) {
// Callers use CONN_TRX_AUTOCOMMIT to bypass REPEATABLE-READ staleness without
// resorting to row locks (e.g. FOR UPDATE) or to make small out-of-band commits
// during larger transactions. This is useful for avoiding lock contention.
// Assuming all servers are of the same type (or similar), which is overwhelmingly
// the case, use the primary server information to get the attributes. The information
// for $i cannot be used since it might be DB_REPLICA, which might require connection
// attempts in order to be resolved into a real server index.
$attributes = $this->getServerAttributes( ServerInfo::WRITER_INDEX );
if ( $attributes[Database::ATTR_DB_LEVEL_LOCKING] ) {
// The RDBMS does not support concurrent writes (e.g. SQLite), so attempts
// to use separate connections would just cause self-deadlocks. Note that
// REPEATABLE-READ staleness is not an issue since DB-level locking means
// that transactions are Strict Serializable anyway.
$flags &= ~self::CONN_TRX_AUTOCOMMIT;
$type = $this->serverInfo->getServerType( ServerInfo::WRITER_INDEX );
$this->logger->info( __METHOD__ . ": CONN_TRX_AUTOCOMMIT disallowed ($type)" );
} elseif ( isset( $this->tempTablesOnlyMode[$domain] ) ) {
// T202116: integration tests are active and queries should be all be using
// temporary clone tables (via prefix). Such tables are not visible across
// different connections nor can there be REPEATABLE-READ snapshot staleness,
// so use the same connection for everything.
$flags &= ~self::CONN_TRX_AUTOCOMMIT;
}
}
return $flags;
}
/**
* @param IDatabase $conn
* @param int $flags
* @throws DBUnexpectedError
*/
private function enforceConnectionFlags( IDatabase $conn, $flags ) {
if (
self::fieldHasBit( $flags, self::CONN_TRX_AUTOCOMMIT ) ||
// Handles with open transactions are avoided since they might be subject
// to REPEATABLE-READ snapshots, which could affect the lag estimate query.
self::fieldHasBit( $flags, self::CONN_UNTRACKED_GAUGE )
) {
if ( $conn->trxLevel() ) {
throw new DBUnexpectedError(
$conn,
'Handle requested with autocommit-mode yet it has a transaction'
);
}
$conn->clearFlag( $conn::DBO_TRX ); // auto-commit mode
}
}
/**
* @param array $loads
* @param int|float $maxLag Restrict the maximum allowed lag to this many seconds, or INF for no max
* @return int|string|false
*/
private function getRandomNonLagged( array $loads, $maxLag = INF ) {
$lags = $this->getLagTimes();
# Unset excessively lagged servers
foreach ( $lags as $i => $lag ) {
if ( $i !== ServerInfo::WRITER_INDEX ) {
# How much lag this server nominally is allowed to have
$maxServerLag = $this->serverInfo->getServerMaxLag( $i ); // default
# Constrain that further by $maxLag argument
$maxServerLag = min( $maxServerLag, $maxLag );
$srvName = $this->serverInfo->getServerName( $i );
if ( $lag === false && !is_infinite( $maxServerLag ) ) {
$this->logger->debug(
__METHOD__ . ": server {db_server} is not replicating?",
[ 'db_server' => $srvName ]
);
unset( $loads[$i] );
} elseif ( $lag > $maxServerLag ) {
$this->logger->debug(
__METHOD__ .
": server {db_server} has {lag} seconds of lag (>= {maxlag})",
[ 'db_server' => $srvName, 'lag' => $lag, 'maxlag' => $maxServerLag ]
);
unset( $loads[$i] );
}
}
}
if ( array_sum( $loads ) == 0 ) {
// All the replicas with non-zero load are lagged and the primary has zero load.
// Inform caller so that it can use switch to read-only mode and use a lagged replica.
return false;
}
# Return a random representative of the remainder
return ArrayUtils::pickRandom( $loads );
}
public function getReaderIndex( $group = false ) {
$group = is_string( $group ) ? $group : self::GROUP_GENERIC;
if ( !$this->serverInfo->hasReplicaServers() ) {
// There is only one possible server to use (the primary)
return ServerInfo::WRITER_INDEX;
}
$index = $this->getExistingReaderIndex( $group );
if ( $index !== self::READER_INDEX_NONE ) {
// A reader index was already selected for this query group. Keep using it,
// since any session replication position was already waited on and any
// active transaction will be reused (e.g. for point-in-time snapshots).
return $index;
}
// Get the server weight array for this load group
$loads = $this->groupLoads[$group] ?? [];
if ( !$loads ) {
$this->logger->info( __METHOD__ . ": no loads for group $group" );
return false;
}
// Load any session replication positions, before any connection attempts,
// since reading them afterwards can only cause more delay due to possibly
// seeing even higher replication positions (e.g. from concurrent requests).
$this->loadSessionPrimaryPos();
// Scale the configured load ratios according to each server's load/state.
// This can sometimes trigger server connections due to cache regeneration.
$this->loadMonitor->scaleLoads( $loads );
// Pick a server, accounting for weight, load, lag, and session consistency
$i = $this->pickReaderIndex( $loads );
if ( $i === false ) {
// Connection attempts failed
return false;
}
// If data seen by queries is expected to reflect writes from a prior transaction,
// then wait for the chosen server to apply those changes. This is used to improve
// session consistency.
if ( !$this->awaitSessionPrimaryPos( $i ) ) {
// Data will be outdated compared to what was expected
$this->setLaggedReplicaMode();
}
// Keep using this server for DB_REPLICA handles for this group
if ( $i < 0 ) {
throw new UnexpectedValueException( "Cannot set a negative read server index" );
}
$this->readIndexByGroup[$group] = $i;
$serverName = $this->getServerName( $i );
$this->logger->debug( __METHOD__ . ": using server $serverName for group '$group'" );
return $i;
}
/**
* Get the server index chosen for DB_REPLICA connections for the given query group
*
* @param string $group Query group; use false for the generic group
* @return int Specific server index or LoadBalancer::READER_INDEX_NONE if none was chosen
*/
protected function getExistingReaderIndex( $group ) {
return $this->readIndexByGroup[$group] ?? self::READER_INDEX_NONE;
}
/**
* Pick a server that is reachable, preferably non-lagged, and return its server index
*
* This will leave the server connection open within the pool for reuse
*
* @param array $loads List of server weights
* @return int|false reader index or false
*/
private function pickReaderIndex( array $loads ) {
if ( $loads === [] ) {
throw new InvalidArgumentException( "Server configuration array is empty" );
}
// Quickly look through the available servers for a server that meets criteria...
$currentLoads = $loads;
$i = false;
while ( count( $currentLoads ) ) {
if ( $this->waitForPos && $this->waitForPos->asOfTime() ) {
$this->logger->debug( __METHOD__ . ": session has replication position" );
// ChronologyProtector::getSessionPrimaryPos called in $this->loadSessionPrimaryPos()
// sets "waitForPos" for session consistency.
// This triggers doWait() after connect, so it's especially good to
// avoid lagged servers so as to avoid excessive delay in that method.
$ago = microtime( true ) - $this->waitForPos->asOfTime();
// Aim for <= 1 second of waiting (being too picky can backfire)
$i = $this->getRandomNonLagged( $currentLoads, $ago + 1 );
} else {
// Any server with less lag than it's 'max lag' param is preferable
$i = $this->getRandomNonLagged( $currentLoads );
}
if ( $i === false && count( $currentLoads ) ) {
$this->setLaggedReplicaMode();
// All replica DBs lagged, just pick anything.
$i = ArrayUtils::pickRandom( $currentLoads );
}
if ( $i === false ) {
// pickRandom() returned false.
// This is permanent and means the configuration or LoadMonitor
// wants us to return false.
$this->logger->debug( __METHOD__ . ": no suitable server found" );
return false;
}
$serverName = $this->getServerName( $i );
$this->logger->debug( __METHOD__ . ": connecting to $serverName..." );
// Get a connection to this server without triggering complementary connections
// to other servers (due to things like lag or read-only checks). We want to avoid
// the risk of overhead and recursion here.
$conn = $this->getServerConnection( $i, self::DOMAIN_ANY, self::CONN_SILENCE_ERRORS );
if ( !$conn ) {
$this->logger->warning( __METHOD__ . ": failed connecting to $serverName" );
unset( $currentLoads[$i] ); // avoid this server next iteration
continue;
}
// Return this server
break;
}
// If all servers were down, quit now
if ( $currentLoads === [] ) {
$this->logger->error( __METHOD__ . ": all servers down" );
}
return $i;
}
public function waitForAll( DBPrimaryPos $pos, $timeout = null ) {
$timeout = $timeout ?: self::MAX_WAIT_DEFAULT;
$oldPos = $this->waitForPos;
try {
$this->waitForPos = $pos;
$ok = true;
foreach ( $this->serverInfo->getStreamingReplicaIndexes() as $i ) {
if ( $this->serverHasLoadInAnyGroup( $i ) ) {
$start = microtime( true );
$ok = $this->awaitSessionPrimaryPos( $i, $timeout ) && $ok;
$timeout -= intval( microtime( true ) - $start );
if ( $timeout <= 0 ) {
break; // timeout reached
}
}
}
return $ok;
} finally {
// Restore the old position; this is used for throttling, not lag-protection
$this->waitForPos = $oldPos;
}
}
/**
* @param int $i Specific server index
* @return bool
*/
private function serverHasLoadInAnyGroup( $i ) {
foreach ( $this->groupLoads as $loadsByIndex ) {
if ( ( $loadsByIndex[$i] ?? 0 ) > 0 ) {
return true;
}
}
return false;
}
public function getAnyOpenConnection( $i, $flags = 0 ) {
$i = ( $i === self::DB_PRIMARY ) ? ServerInfo::WRITER_INDEX : $i;
$conn = false;
foreach ( $this->conns as $type => $poolConnsByServer ) {
if ( $i === self::DB_REPLICA ) {
// Consider all existing connections to any server
$applicableConnsByServer = $poolConnsByServer;
} else {
// Consider all existing connections to a specific server
$applicableConnsByServer = isset( $poolConnsByServer[$i] )
? [ $i => $poolConnsByServer[$i] ]
: [];
}
$conn = $this->pickAnyOpenConnection( $applicableConnsByServer );
if ( $conn ) {
$this->logger->debug( __METHOD__ . ": found '$type' connection to #$i." );
break;
}
}
if ( $conn ) {
$this->enforceConnectionFlags( $conn, $flags );
}
return $conn;
}
/**
* @param Database[][] $connsByServer Map of (server index => array of DB handles)
* @return IDatabase|false An appropriate open connection or false if none found
*/
private function pickAnyOpenConnection( array $connsByServer ) {
foreach ( $connsByServer as $i => $conns ) {
foreach ( $conns as $conn ) {
if ( !$conn->isOpen() ) {
$this->logger->warning(
__METHOD__ .
": pooled DB handle for {db_server} (#$i) has no open connection.",
$this->getConnLogContext( $conn )
);
continue; // some sort of error occurred?
}
return $conn;
}
}
return false;
}
/**
* Wait for a given replica DB to catch up to the primary DB pos stored in "waitForPos"
*
* @see loadSessionPrimaryPos()
*
* @param int $index Specific server index
* @param int|null $timeout Max seconds to wait; default is "waitTimeout"
* @return bool Success
*/
private function awaitSessionPrimaryPos( $index, $timeout = null ) {
$timeout = max( 1, intval( $timeout ?: self::MAX_WAIT_DEFAULT ) );
if ( !$this->waitForPos || $index === ServerInfo::WRITER_INDEX ) {
return true;
}
$srvName = $this->getServerName( $index );
// Check if we already know that the DB has reached this point
$key = $this->srvCache->makeGlobalKey( __CLASS__, 'last-known-pos', $srvName, 'v2' );
/** @var DBPrimaryPos $knownReachedPos */
$position = $this->srvCache->get( $key );
if ( !is_array( $position ) ) {
$knownReachedPos = null;
} else {
$class = $position['_type_'];
$knownReachedPos = $class::newFromArray( $position );
}
if (
$knownReachedPos instanceof DBPrimaryPos &&
$knownReachedPos->hasReached( $this->waitForPos )
) {
$this->logger->debug(
__METHOD__ .
": replica DB {db_server} known to be caught up (pos >= $knownReachedPos).",
[ 'db_server' => $srvName ]
);
return true;
}
$close = false; // close the connection afterwards
$flags = self::CONN_SILENCE_ERRORS;
// Check if there is an existing connection that can be used
$conn = $this->getAnyOpenConnection( $index, $flags );
if ( !$conn ) {
// Get a connection to this server without triggering complementary connections
// to other servers (due to things like lag or read-only checks). We want to avoid
// the risk of overhead and recursion here.
$conn = $this->getServerConnection( $index, self::DOMAIN_ANY, $flags );
if ( !$conn ) {
$this->logger->warning(
__METHOD__ . ': failed to connect to {db_server}',
[ 'db_server' => $srvName ]
);
return false;
}
// Avoid connection spam in waitForAll() when connections
// are made just for the sake of doing this lag check.
$close = true;
}
$this->logger->info(
__METHOD__ .
': waiting for replica DB {db_server} to catch up...',
$this->getConnLogContext( $conn )
);
$result = $conn->primaryPosWait( $this->waitForPos, $timeout );
$ok = ( $result !== null && $result != -1 );
if ( $ok ) {
// Remember that the DB reached this point
$this->srvCache->set( $key, $this->waitForPos->toArray(), BagOStuff::TTL_DAY );
}
if ( $close ) {
$this->closeConnection( $conn );
}
return $ok;
}
public function getConnection( $i, $groups = [], $domain = false, $flags = 0 ) {
return $this->getConnectionRef( $i, $groups, $domain, $flags );
}
public function getConnectionInternal( $i, $groups = [], $domain = false, $flags = 0 ): IDatabase {
$domain = $this->resolveDomainID( $domain );
$group = $this->resolveGroups( $groups, $i );
$flags = $this->sanitizeConnectionFlags( $flags, $i, $domain );
// If given DB_PRIMARY/DB_REPLICA, resolve it to a specific server index. Resolving
// DB_REPLICA might trigger getServerConnection() calls due to the getReaderIndex()
// connectivity checks or LoadMonitor::scaleLoads() server state cache regeneration.
// The use of getServerConnection() instead of getConnection() avoids infinite loops.
$serverIndex = $i;
if ( $i === self::DB_PRIMARY ) {
$serverIndex = ServerInfo::WRITER_INDEX;
} elseif ( $i === self::DB_REPLICA ) {
$groupIndex = $this->getReaderIndex( $group );
if ( $groupIndex !== false ) {
// Group connection succeeded
$serverIndex = $groupIndex;
}
if ( $serverIndex < 0 ) {
$this->reportConnectionError( 'could not connect to any replica DB server' );
}
} elseif ( !$this->serverInfo->hasServerIndex( $i ) ) {
throw new UnexpectedValueException( "Invalid server index index #$i" );
}
// Get an open connection to that server (might trigger a new connection)
return $this->getServerConnection( $serverIndex, $domain, $flags );
}
public function getServerConnection( $i, $domain, $flags = 0 ) {
$domainInstance = DatabaseDomain::newFromId( $domain );
// Number of connections made before getting the server index and handle
$priorConnectionsMade = $this->connectionCounter;
// Get an open connection to this server (might trigger a new connection)
$conn = $this->reuseOrOpenConnectionForNewRef( $i, $domainInstance, $flags );
// Throw an error or otherwise bail out if the connection attempt failed
if ( !( $conn instanceof IDatabase ) ) {
if ( !self::fieldHasBit( $flags, self::CONN_SILENCE_ERRORS ) ) {
$this->reportConnectionError();
}
return false;
}
// Profile any new connections caused by this method
if ( $this->connectionCounter > $priorConnectionsMade ) {
$this->trxProfiler->recordConnection(
$conn->getServerName(),
$conn->getDBname(),
self::fieldHasBit( $flags, self::CONN_INTENT_WRITABLE )
);
}
if ( !$conn->isOpen() ) {
$this->lastErrorConn = $conn;
// Connection was made but later unrecoverably lost for some reason.
// Do not return a handle that will just throw exceptions on use, but
// let the calling code, e.g. getReaderIndex(), try another server.
if ( !self::fieldHasBit( $flags, self::CONN_SILENCE_ERRORS ) ) {
$this->reportConnectionError();
}
return false;
}
return $conn;
}
public function reuseConnection( IDatabase $conn ) {
// no-op
}
public function getConnectionRef( $i, $groups = [], $domain = false, $flags = 0 ): IDatabase {
if ( self::fieldHasBit( $flags, self::CONN_SILENCE_ERRORS ) ) {
throw new UnexpectedValueException(
__METHOD__ . ' got CONN_SILENCE_ERRORS; connection is already deferred'
);
}
$domain = $this->resolveDomainID( $domain );
$role = ( $i === self::DB_PRIMARY || $i === ServerInfo::WRITER_INDEX )
? self::DB_PRIMARY
: self::DB_REPLICA;
return new DBConnRef( $this, [ $i, $groups, $domain, $flags ], $role, $this->modcount );
}
public function getMaintenanceConnectionRef(
$i,
$groups = [],
$domain = false,
$flags = 0
): DBConnRef {
if ( self::fieldHasBit( $flags, self::CONN_SILENCE_ERRORS ) ) {
throw new UnexpectedValueException(
__METHOD__ . ' CONN_SILENCE_ERRORS is not supported'
);
}
$domain = $this->resolveDomainID( $domain );
$role = ( $i === self::DB_PRIMARY || $i === ServerInfo::WRITER_INDEX )
? self::DB_PRIMARY
: self::DB_REPLICA;
return new DBConnRef( $this, [ $i, $groups, $domain, $flags ], $role, $this->modcount );
}
/**
* Get a live connection handle to the given domain
*
* This will reuse an existing tracked connection when possible. In some cases, this
* involves switching the DB domain of an existing handle in order to reuse it. If no
* existing handles can be reused, then a new connection will be made.
*
* @param int $i Specific server index
* @param DatabaseDomain $domain Database domain ID required by the reference
* @param int $flags Bit field of class CONN_* constants
* @return IDatabase|null Database or null on error
* @throws DBError When database selection fails
* @throws InvalidArgumentException When the server index is invalid
* @throws UnexpectedValueException When the DB domain of the connection is corrupted
* @throws DBAccessError If disable() was called
*/
private function reuseOrOpenConnectionForNewRef( $i, DatabaseDomain $domain, $flags = 0 ) {
// Figure out which connection pool to use based on the flags
if ( $this->fieldHasBit( $flags, self::CONN_UNTRACKED_GAUGE ) ) {
// Use low timeouts, use autocommit mode, ignore transaction rounds
$category = self::CATEGORY_GAUGE;
} elseif ( self::fieldHasBit( $flags, self::CONN_TRX_AUTOCOMMIT ) ) {
// Use autocommit mode, ignore transaction rounds
$category = self::CATEGORY_AUTOCOMMIT;
} else {
// Respect DBO_DEFAULT, respect transaction rounds
$category = self::CATEGORY_ROUND;
}
$conn = null;
// Reuse a free connection in the pool from any domain if possible. There should only
// be one connection in this pool unless either:
// - a) IDatabase::databasesAreIndependent() returns true (e.g. postgres) and two
// or more database domains have been used during the load balancer's lifetime
// - b) Two or more nested function calls used getConnection() on different domains.
// Normally, callers should use getConnectionRef() instead of getConnection().
foreach ( ( $this->conns[$category][$i] ?? [] ) as $poolConn ) {
// Check if any required DB domain changes for the new reference are possible
// Calling selectDomain() would trigger a reconnect, which will break if a
// transaction is active or if there is any other meaningful session state.
$isShareable = !(
$poolConn->databasesAreIndependent() &&
$domain->getDatabase() !== null &&
$domain->getDatabase() !== $poolConn->getDBname()
);
if ( $isShareable ) {
$conn = $poolConn;
// Make any required DB domain changes for the new reference
if ( !$domain->isUnspecified() ) {
$conn->selectDomain( $domain );
}
$this->logger->debug( __METHOD__ . ": reusing connection for $i/$domain" );
break;
}
}
// If necessary, try to open a new connection and add it to the pool
if ( !$conn ) {
$conn = $this->reallyOpenConnection(
$i,
$domain,
[ self::INFO_CONN_CATEGORY => $category ]
);
if ( $conn->isOpen() ) {
// Make Database::isReadOnly() respect server-side and configuration-based
// read-only mode. Note that replica handles are always seen as read-only
// in Database::isReadOnly() and Database::assertIsWritablePrimary().
if ( $i === ServerInfo::WRITER_INDEX ) {
if ( $this->readOnlyReason !== false ) {
$readOnlyReason = $this->readOnlyReason;
} elseif ( $this->isPrimaryRunningReadOnly( $conn ) ) {
$readOnlyReason = 'The primary database server is running in read-only mode.';
} else {
$readOnlyReason = false;
}
$conn->setLBInfo( $conn::LB_READ_ONLY_REASON, $readOnlyReason );
}
// Connection obtained; check if it belongs to a tracked connection category
if ( isset( $this->conns[$category] ) ) {
// Track this connection for future reuse
$this->conns[$category][$i][] = $conn;
}
} else {
$this->logger->warning( __METHOD__ . ": connection error for $i/$domain" );
$this->lastErrorConn = $conn;
$conn = null;
}
}
if ( $conn instanceof IDatabase ) {
// Check to make sure that the right domain is selected
$this->assertConnectionDomain( $conn, $domain );
// Check to make sure that the CONN_* flags are respected
$this->enforceConnectionFlags( $conn, $flags );
}
return $conn;
}
/**
* Sanity check to make sure that the right domain is selected
*
* @param Database $conn
* @param DatabaseDomain $domain
* @throws DBUnexpectedError
*/
private function assertConnectionDomain( Database $conn, DatabaseDomain $domain ) {
if ( !$domain->isCompatible( $conn->getDomainID() ) ) {
throw new UnexpectedValueException(
"Got connection to '{$conn->getDomainID()}', but expected one for '{$domain}'"
);
}
}
public function getServerAttributes( $i ) {
return $this->databaseFactory->attributesFromType(
$this->getServerType( $i ),
$this->serverInfo->getServerDriver( $i )
);
}
/**
* Open a new network connection to a server (uncached)
*
* Returns a Database object whether or not the connection was successful.
*
* @param int $i Specific server index
* @param DatabaseDomain $domain Domain the connection is for, possibly unspecified
* @param array $lbInfo Additional information for setLBInfo()
* @return Database
* @throws DBAccessError
* @throws InvalidArgumentException
*/
protected function reallyOpenConnection( $i, DatabaseDomain $domain, array $lbInfo ) {
if ( $this->disabled ) {
throw new DBAccessError();
}
$server = $this->serverInfo->getServerInfoStrict( $i );
if ( $lbInfo[self::INFO_CONN_CATEGORY] === self::CATEGORY_GAUGE ) {
// Use low connection/read timeouts for connection used for gauging server health.
// Gauge information should be cached and used to avoid outages. Indefinite hanging
// while gauging servers would do the opposite.
$server['connectTimeout'] = min( 1, $server['connectTimeout'] ?? INF );
$server['receiveTimeout'] = min( 1, $server['receiveTimeout'] ?? INF );
// Avoid implicit transactions and avoid any SET query for session variables during
// Database::open(). If a server becomes slow, every extra query can cause significant
// delays, even with low connect/receive timeouts.
$server['flags'] ??= 0;
$server['flags'] &= ~IDatabase::DBO_DEFAULT;
$server['flags'] |= IDatabase::DBO_GAUGE;
} else {
// Use implicit transactions unless explicitly configured otherwise
$server['flags'] ??= IDatabase::DBO_DEFAULT;
}
if ( !empty( $server['is static'] ) ) {
$topologyRole = IDatabase::ROLE_STATIC_CLONE;
} else {
$topologyRole = ( $i === ServerInfo::WRITER_INDEX )
? IDatabase::ROLE_STREAMING_MASTER
: IDatabase::ROLE_STREAMING_REPLICA;
}
$conn = $this->databaseFactory->create(
$server['type'],
array_merge( $server, [
// Basic replication role information
'topologyRole' => $topologyRole,
// Use the database specified in $domain (null means "none or entrypoint DB");
// fallback to the $server default if the RDBMs is an embedded library using a
// file on disk since there would be nothing to access to without a DB/file name.
'dbname' => $this->getServerAttributes( $i )[Database::ATTR_DB_IS_FILE]
? ( $domain->getDatabase() ?? $server['dbname'] ?? null )
: $domain->getDatabase(),
// Override the $server default schema with that of $domain if specified
'schema' => $domain->getSchema(),
// Use the table prefix specified in $domain
'tablePrefix' => $domain->getTablePrefix(),
'srvCache' => $this->srvCache,
'logger' => $this->logger,
'errorLogger' => $this->errorLogger,
'trxProfiler' => $this->trxProfiler,
'lbInfo' => [ self::INFO_SERVER_INDEX => $i ] + $lbInfo
] ),
Database::NEW_UNCONNECTED
);
// Set alternative table/index names before any queries can be issued
$conn->setTableAliases( $this->tableAliases );
$conn->setIndexAliases( $this->indexAliases );
// Account for any active transaction round and listeners
if ( $i === ServerInfo::WRITER_INDEX ) {
if ( $this->trxRoundId !== false ) {
$this->applyTransactionRoundFlags( $conn );
}
foreach ( $this->trxRecurringCallbacks as $name => $callback ) {
$conn->setTransactionListener( $name, $callback );
}
}
// Make the connection handle live
try {
$conn->initConnection();
++$this->connectionCounter;
} catch ( DBConnectionError $e ) {
$this->lastErrorConn = $conn;
// ignore; let the DB handle the logging
}
if ( $conn->isOpen() ) {
$this->logger->debug( __METHOD__ . ": opened new connection for $i/$domain" );
} else {
$this->logger->warning(
__METHOD__ . ": connection error for $i/{db_domain}",
[ 'db_domain' => $domain->getId() ]
);
}
// Log when many connection are made during a single request/script
$count = 0;
foreach ( $this->conns as $poolConnsByServer ) {
foreach ( $poolConnsByServer as $serverConns ) {
$count += count( $serverConns );
}
}
if ( $count >= self::CONN_HELD_WARN_THRESHOLD ) {
$this->logger->warning(
__METHOD__ . ": {connections}+ connections made (primary={primarydb})",
$this->getConnLogContext(
$conn,
[
'connections' => $count,
'primarydb' => $this->serverInfo->getPrimaryServerName(),
'db_domain' => $domain->getId()
]
)
);
}
$this->assertConnectionDomain( $conn, $domain );
return $conn;
}
/**
* Make sure that any "waitForPos" replication positions are loaded and available
*
* Each load balancer cluster has up to one replication position for the session.
* These are used when data read by queries is expected to reflect writes caused
* by a prior request/script from the same client.
*
* @see awaitSessionPrimaryPos()
*/
private function loadSessionPrimaryPos() {
if ( !$this->chronologyProtectorCalled && $this->chronologyProtector ) {
$this->chronologyProtectorCalled = true;
$pos = $this->chronologyProtector->getSessionPrimaryPos( $this );
$this->logger->debug( __METHOD__ . ': executed chronology callback.' );
if ( $pos ) {
if ( !$this->waitForPos || $pos->hasReached( $this->waitForPos ) ) {
$this->waitForPos = $pos;
}
}
}
}
/**
* @param string $extraLbError Separat load balancer error
* @throws DBConnectionError
* @return never
*/
private function reportConnectionError( $extraLbError = '' ) {
if ( $this->lastErrorConn instanceof IDatabase ) {
$srvName = $this->lastErrorConn->getServerName();
$lastDbError = $this->lastErrorConn->lastError() ?: 'unknown error';
$exception = new DBConnectionError(
$this->lastErrorConn,
$extraLbError
? "{$extraLbError}; {$lastDbError} ({$srvName})"
: "{$lastDbError} ({$srvName})"
);
if ( $extraLbError ) {
$this->logger->warning(
__METHOD__ . ": $extraLbError; {last_error} ({db_server})",
$this->getConnLogContext(
$this->lastErrorConn,
[
'method' => __METHOD__,
'last_error' => $lastDbError
]
)
);
}
} else {
$exception = new DBConnectionError(
null,
$extraLbError ?: 'could not connect to the DB server'
);
if ( $extraLbError ) {
$this->logger->error(
__METHOD__ . ": $extraLbError",
[
'method' => __METHOD__,
'last_error' => '(last connection error missing)'
]
);
}
}
throw $exception;
}
public function getWriterIndex() {
return ServerInfo::WRITER_INDEX;
}
public function getServerCount() {
return $this->serverInfo->getServerCount();
}
public function hasReplicaServers() {
return $this->serverInfo->hasReplicaServers();
}
public function hasStreamingReplicaServers() {
return $this->serverInfo->hasStreamingReplicaServers();
}
public function getServerName( $i ): string {
return $this->serverInfo->getServerName( $i );
}
public function getServerInfo( $i ) {
return $this->serverInfo->getServerInfo( $i );
}
public function getServerType( $i ) {
return $this->serverInfo->getServerType( $i );
}
public function getPrimaryPos() {
$conn = $this->getAnyOpenConnection( ServerInfo::WRITER_INDEX );
if ( $conn ) {
return $conn->getPrimaryPos();
}
$conn = $this->getConnectionInternal( ServerInfo::WRITER_INDEX, self::CONN_SILENCE_ERRORS );
// @phan-suppress-next-line PhanRedundantCondition
if ( !$conn ) {
$this->reportConnectionError();
}
try {
return $conn->getPrimaryPos();
} finally {
$this->closeConnection( $conn );
}
}
/**
* Apply updated configuration.
*
* This only unregisters servers that were removed in the new configuration.
* It does not register new servers nor update the group load weights.
*
* This invalidates any open connections. However, existing connections may continue to be
* used while they are in an active transaction. In that case, the old connection will be
* discarded on the first operation after the transaction is complete. The next operation
* will use a new connection based on the new configuration.
*
* @internal for use by LBFactory::reconfigure()
*
* @see DBConnRef::ensureConnection()
* @see LBFactory::reconfigure()
*
* @param array $params A database configuration array, see $wgLBFactoryConf.
*
* @return void
*/
public function reconfigure( array $params ) {
$anyServerDepooled = false;
$paramServers = $params['servers'];
$newIndexByServerIndex = $this->serverInfo->reconfigureServers( $paramServers );
foreach ( $newIndexByServerIndex as $i => $ni ) {
if ( $ni !== null ) {
// Server still exists in the new config
$newWeightByGroup = $paramServers[$ni]['groupLoads'] ?? [];
$newWeightByGroup[ILoadBalancer::GROUP_GENERIC] = $paramServers[$ni]['load'];
// Check if the server was removed from any load groups
foreach ( $this->groupLoads as $group => $weightByIndex ) {
if ( isset( $weightByIndex[$i] ) && !isset( $newWeightByGroup[$group] ) ) {
// Server no longer in this load group in the new config
$anyServerDepooled = true;
unset( $this->groupLoads[$group][$i] );
}
}
} else {
// Server no longer exists in the new config
$anyServerDepooled = true;
// Note that if the primary server is depooled and a replica server promoted
// to new primary, then DB_PRIMARY handles will fail with server index errors
foreach ( $this->groupLoads as $group => $loads ) {
unset( $this->groupLoads[$group][$i] );
}
}
}
if ( $anyServerDepooled ) {
// NOTE: We could close all connection here, but some may be in the middle of
// a transaction. So instead, we leave it to DBConnRef to close the
// connection when it detects that the modcount has changed and no
// transaction is open.
$this->logger->info( 'Reconfiguring dbs!' );
// Unpin DB_REPLICA connection groups from server indexes
$this->readIndexByGroup = [];
// We could close all connection here, but some may be in the middle of a
// transaction. So instead, we leave it to DBConnRef to close the connection
// when it detects that the modcount has changed and no transaction is open.
$this->conns = self::newTrackedConnectionsArray();
// Bump modification counter to invalidate the connections held by DBConnRef
// instances. This will cause the next call to a method on the DBConnRef
// to get a new connection from getConnectionInternal()
$this->modcount++;
}
}
public function disable( $fname = __METHOD__ ) {
$this->closeAll( $fname );
$this->disabled = true;
}
public function closeAll( $fname = __METHOD__ ) {
/** @noinspection PhpUnusedLocalVariableInspection */
$scope = ScopedCallback::newScopedIgnoreUserAbort();
foreach ( $this->getOpenConnections() as $conn ) {
$conn->close( $fname );
}
$this->conns = self::newTrackedConnectionsArray();
}
/**
* Close a connection
*
* Using this function makes sure the LoadBalancer knows the connection is closed.
* If you use $conn->close() directly, the load balancer won't update its state.
*
* @param IDatabase $conn
*/
private function closeConnection( IDatabase $conn ) {
if ( $conn instanceof DBConnRef ) {
// Avoid calling close() but still leaving the handle in the pool
throw new RuntimeException( 'Cannot close DBConnRef instance; it must be shareable' );
}
$domain = $conn->getDomainID();
$serverIndex = $conn->getLBInfo( self::INFO_SERVER_INDEX );
if ( $serverIndex === null ) {
throw new UnexpectedValueException( "Handle on '$domain' missing server index" );
}
$srvName = $this->serverInfo->getServerName( $serverIndex );
$found = false;
foreach ( $this->conns as $type => $poolConnsByServer ) {
$key = array_search( $conn, $poolConnsByServer[$serverIndex] ?? [], true );
if ( $key !== false ) {
$found = true;
unset( $this->conns[$type][$serverIndex][$key] );
}
}
if ( !$found ) {
$this->logger->warning(
__METHOD__ .
": orphaned connection to database {$this->stringifyConn( $conn )} at '$srvName'."
);
}
$this->logger->debug(
__METHOD__ .
": closing connection to database {$this->stringifyConn( $conn )} at '$srvName'."
);
$conn->close( __METHOD__ );
}
public function finalizePrimaryChanges( $fname = __METHOD__ ) {
$this->assertTransactionRoundStage( [ self::ROUND_CURSORY, self::ROUND_FINALIZED ] );
/** @noinspection PhpUnusedLocalVariableInspection */
$scope = ScopedCallback::newScopedIgnoreUserAbort();
$this->trxRoundStage = self::ROUND_ERROR; // "failed" until proven otherwise
// Loop until callbacks stop adding callbacks on other connections
$total = 0;
do {
$count = 0; // callbacks execution attempts
foreach ( $this->getOpenPrimaryConnections() as $conn ) {
// Run any pre-commit callbacks while leaving the post-commit ones suppressed.
// Any error should cause all (peer) transactions to be rolled back together.
$count += $conn->runOnTransactionPreCommitCallbacks();
}
$total += $count;
} while ( $count > 0 );
// Defer post-commit callbacks until after COMMIT/ROLLBACK happens on all handles
foreach ( $this->getOpenPrimaryConnections() as $conn ) {
$conn->setTrxEndCallbackSuppression( true );
}
$this->trxRoundStage = self::ROUND_FINALIZED;
return $total;
}
public function approvePrimaryChanges( int $maxWriteDuration, $fname = __METHOD__ ) {
$this->assertTransactionRoundStage( self::ROUND_FINALIZED );
/** @noinspection PhpUnusedLocalVariableInspection */
$scope = ScopedCallback::newScopedIgnoreUserAbort();
$this->trxRoundStage = self::ROUND_ERROR; // "failed" until proven otherwise
foreach ( $this->getOpenPrimaryConnections() as $conn ) {
// Any atomic sections should have been closed by now and there definitely should
// not be any open transactions started by begin() from callers outside Database.
if ( $conn->explicitTrxActive() ) {
throw new DBTransactionError(
$conn,
"Explicit transaction still active; a caller might have failed to call " .
"endAtomic() or cancelAtomic()."
);
}
// Assert that the time to replicate the transaction will be reasonable.
// If this fails, then all DB transactions will be rollback back together.
$time = $conn->pendingWriteQueryDuration( $conn::ESTIMATE_DB_APPLY );
if ( $maxWriteDuration > 0 ) {
if ( $time > $maxWriteDuration ) {
$humanTimeSec = round( $time, 3 );
throw new DBTransactionSizeError(
$conn,
"Transaction spent {time}s in writes, exceeding the {$maxWriteDuration}s limit",
// Message parameters for: transaction-duration-limit-exceeded
[ $time, $maxWriteDuration ],
null,
[ 'time' => $humanTimeSec ]
);
} elseif ( $time > 0 ) {
$timeMs = $time * 1000;
$humanTimeMs = round( $timeMs, $timeMs > 1 ? 0 : 3 );
$this->logger->debug(
"Transaction spent {time_ms}ms in writes, under the {$maxWriteDuration}s limit",
[ 'time_ms' => $humanTimeMs ]
);
}
}
// If a connection sits idle for too long it might be dropped, causing transaction
// writes and session locks to be lost. Ping all the server connections before making
// any attempt to commit the transactions belonging to the active transaction round.
if ( $conn->writesOrCallbacksPending() || $conn->sessionLocksPending() ) {
if ( !$conn->ping() ) {
throw new DBTransactionError(
$conn,
"Pre-commit ping failed on server {$conn->getServerName()}"
);
}
}
}
$this->trxRoundStage = self::ROUND_APPROVED;
}
public function beginPrimaryChanges( $fname = __METHOD__ ) {
if ( $this->trxRoundId !== false ) {
throw new DBTransactionError(
null,
"Transaction round '{$this->trxRoundId}' already started"
);
}
$this->assertTransactionRoundStage( self::ROUND_CURSORY );
/** @noinspection PhpUnusedLocalVariableInspection */
$scope = ScopedCallback::newScopedIgnoreUserAbort();
// Clear any empty transactions (no writes/callbacks) from the implicit round
$this->flushPrimarySnapshots( $fname );
$this->trxRoundId = $fname;
$this->trxRoundStage = self::ROUND_ERROR; // "failed" until proven otherwise
// Mark applicable handles as participating in this explicit transaction round.
// For each of these handles, any writes and callbacks will be tied to a single
// transaction. The (peer) handles will reject begin()/commit() calls unless they
// are part of an en masse commit or an en masse rollback.
foreach ( $this->getOpenPrimaryConnections() as $conn ) {
$this->applyTransactionRoundFlags( $conn );
}
$this->trxRoundStage = self::ROUND_CURSORY;
}
public function commitPrimaryChanges( $fname = __METHOD__ ) {
$this->assertTransactionRoundStage( self::ROUND_APPROVED );
/** @noinspection PhpUnusedLocalVariableInspection */
$scope = ScopedCallback::newScopedIgnoreUserAbort();
$failures = [];
$restore = ( $this->trxRoundId !== false );
$this->trxRoundId = false;
$this->trxRoundStage = self::ROUND_ERROR; // "failed" until proven otherwise
// Commit any writes and clear any snapshots as well (callbacks require AUTOCOMMIT).
// Note that callbacks should already be suppressed due to finalizePrimaryChanges().
foreach ( $this->getOpenPrimaryConnections() as $conn ) {
try {
$conn->commit( $fname, $conn::FLUSHING_ALL_PEERS );
} catch ( DBError $e ) {
( $this->errorLogger )( $e );
$failures[] = "{$conn->getServerName()}: {$e->getMessage()}";
}
}
if ( $failures ) {
throw new DBTransactionError(
null,
"Commit failed on server(s) " . implode( "\n", array_unique( $failures ) )
);
}
if ( $restore ) {
// Unmark handles as participating in this explicit transaction round
foreach ( $this->getOpenPrimaryConnections() as $conn ) {
$this->undoTransactionRoundFlags( $conn );
}
}
$this->trxRoundStage = self::ROUND_COMMIT_CALLBACKS;
}
public function runPrimaryTransactionIdleCallbacks( $fname = __METHOD__ ) {
if ( $this->trxRoundStage === self::ROUND_COMMIT_CALLBACKS ) {
$type = IDatabase::TRIGGER_COMMIT;
} elseif ( $this->trxRoundStage === self::ROUND_ROLLBACK_CALLBACKS ) {
$type = IDatabase::TRIGGER_ROLLBACK;
} else {
throw new DBTransactionError(
null,
"Transaction should be in the callback stage (not '{$this->trxRoundStage}')"
);
}
/** @noinspection PhpUnusedLocalVariableInspection */
$scope = ScopedCallback::newScopedIgnoreUserAbort();
$oldStage = $this->trxRoundStage;
$this->trxRoundStage = self::ROUND_ERROR; // "failed" until proven otherwise
// Now that the COMMIT/ROLLBACK step is over, enable post-commit callback runs
foreach ( $this->getOpenPrimaryConnections() as $conn ) {
$conn->setTrxEndCallbackSuppression( false );
}
$errors = [];
$fname = __METHOD__;
// Loop until callbacks stop adding callbacks on other connections
do {
// Run any pending callbacks for each connection...
$count = 0; // callback execution attempts
foreach ( $this->getOpenPrimaryConnections() as $conn ) {
if ( $conn->trxLevel() ) {
continue; // retry in the next iteration, after commit() is called
}
$count += $conn->runOnTransactionIdleCallbacks( $type, $errors );
}
// Clear out any active transactions left over from callbacks...
foreach ( $this->getOpenPrimaryConnections() as $conn ) {
if ( $conn->writesPending() ) {
// A callback from another handle wrote to this one and DBO_TRX is set
$fnames = implode( ', ', $conn->pendingWriteAndCallbackCallers() );
$this->logger->warning(
"$fname: found writes pending ($fnames).",
$this->getConnLogContext(
$conn,
[ 'exception' => new RuntimeException() ]
)
);
} elseif ( $conn->trxLevel() ) {
// A callback from another handle read from this one and DBO_TRX is set,
// which can easily happen if there is only one DB (no replicas)
$this->logger->debug( "$fname: found empty transaction." );
}
try {
$conn->commit( $fname, $conn::FLUSHING_ALL_PEERS );
} catch ( DBError $ex ) {
$errors[] = $ex;
}
}
} while ( $count > 0 );
$this->trxRoundStage = $oldStage;
return $errors[0] ?? null;
}
public function runPrimaryTransactionListenerCallbacks( $fname = __METHOD__ ) {
if ( $this->trxRoundStage === self::ROUND_COMMIT_CALLBACKS ) {
$type = IDatabase::TRIGGER_COMMIT;
} elseif ( $this->trxRoundStage === self::ROUND_ROLLBACK_CALLBACKS ) {
$type = IDatabase::TRIGGER_ROLLBACK;
} else {
throw new DBTransactionError(
null,
"Transaction should be in the callback stage (not '{$this->trxRoundStage}')"
);
}
/** @noinspection PhpUnusedLocalVariableInspection */
$scope = ScopedCallback::newScopedIgnoreUserAbort();
$errors = [];
$this->trxRoundStage = self::ROUND_ERROR; // "failed" until proven otherwise
foreach ( $this->getOpenPrimaryConnections() as $conn ) {
$conn->runTransactionListenerCallbacks( $type, $errors );
}
$this->trxRoundStage = self::ROUND_CURSORY;
return $errors[0] ?? null;
}
public function rollbackPrimaryChanges( $fname = __METHOD__ ) {
/** @noinspection PhpUnusedLocalVariableInspection */
$scope = ScopedCallback::newScopedIgnoreUserAbort();
$restore = ( $this->trxRoundId !== false );
$this->trxRoundId = false;
$this->trxRoundStage = self::ROUND_ERROR; // "failed" until proven otherwise
foreach ( $this->getOpenPrimaryConnections() as $conn ) {
$conn->rollback( $fname, $conn::FLUSHING_ALL_PEERS );
}
if ( $restore ) {
// Unmark handles as participating in this explicit transaction round
foreach ( $this->getOpenPrimaryConnections() as $conn ) {
$this->undoTransactionRoundFlags( $conn );
}
}
$this->trxRoundStage = self::ROUND_ROLLBACK_CALLBACKS;
}
public function flushPrimarySessions( $fname = __METHOD__ ) {
$this->assertTransactionRoundStage( [ self::ROUND_CURSORY ] );
if ( $this->hasPrimaryChanges() ) {
// Any transaction should have been rolled back beforehand
throw new DBTransactionError( null, "Cannot reset session while writes are pending" );
}
foreach ( $this->getOpenPrimaryConnections() as $conn ) {
$conn->flushSession( $fname, $conn::FLUSHING_ALL_PEERS );
}
}
/**
* @param string|string[] $stage
* @throws DBTransactionError
*/
private function assertTransactionRoundStage( $stage ) {
$stages = (array)$stage;
if ( !in_array( $this->trxRoundStage, $stages, true ) ) {
$stageList = implode(
'/',
array_map( static function ( $v ) {
return "'$v'";
}, $stages )
);
throw new DBTransactionError(
null,
"Transaction round stage must be $stageList (not '{$this->trxRoundStage}')"
);
}
}
/**
* Make all DB servers with DBO_DEFAULT/DBO_TRX set join the transaction round
*
* Some servers may have neither flag enabled, meaning that they opt out of such
* transaction rounds and remain in auto-commit mode. Such behavior might be desired
* when a DB server is used for something like simple key/value storage.
*
* @param Database $conn
*/
private function applyTransactionRoundFlags( Database $conn ) {
if ( $conn->getLBInfo( self::INFO_CONN_CATEGORY ) !== self::CATEGORY_ROUND ) {
return; // transaction rounds do not apply to these connections
}
if ( $conn->getFlag( $conn::DBO_DEFAULT ) ) {
// DBO_TRX is controlled entirely by CLI mode presence with DBO_DEFAULT.
// Force DBO_TRX even in CLI mode since a commit round is expected soon.
$conn->setFlag( $conn::DBO_TRX, $conn::REMEMBER_PRIOR );
}
if ( $conn->getFlag( $conn::DBO_TRX ) ) {
$conn->setLBInfo( $conn::LB_TRX_ROUND_ID, $this->trxRoundId );
}
}
/**
* @param Database $conn
*/
private function undoTransactionRoundFlags( Database $conn ) {
if ( $conn->getLBInfo( self::INFO_CONN_CATEGORY ) !== self::CATEGORY_ROUND ) {
return; // transaction rounds do not apply to these connections
}
if ( $conn->getFlag( $conn::DBO_TRX ) ) {
$conn->setLBInfo( $conn::LB_TRX_ROUND_ID, null ); // remove the round ID
}
if ( $conn->getFlag( $conn::DBO_DEFAULT ) ) {
$conn->restoreFlags( $conn::RESTORE_PRIOR );
}
}
public function flushReplicaSnapshots( $fname = __METHOD__ ) {
foreach ( $this->conns as $poolConnsByServer ) {
foreach ( $poolConnsByServer as $serverIndex => $serverConns ) {
if ( $serverIndex === ServerInfo::WRITER_INDEX ) {
continue; // skip primary
}
foreach ( $serverConns as $conn ) {
$conn->flushSnapshot( $fname );
}
}
}
}
public function flushPrimarySnapshots( $fname = __METHOD__ ) {
foreach ( $this->getOpenPrimaryConnections() as $conn ) {
$conn->flushSnapshot( $fname );
}
}
public function hasPrimaryConnection() {
return (bool)$this->getAnyOpenConnection( ServerInfo::WRITER_INDEX );
}
public function hasPrimaryChanges() {
foreach ( $this->getOpenPrimaryConnections() as $conn ) {
if ( $conn->writesOrCallbacksPending() ) {
return true;
}
}
return false;
}
public function lastPrimaryChangeTimestamp() {
$lastTime = false;
foreach ( $this->getOpenPrimaryConnections() as $conn ) {
$lastTime = max( $lastTime, $conn->lastDoneWrites() );
}
return $lastTime;
}
public function hasOrMadeRecentPrimaryChanges( $age = null ) {
$age ??= self::MAX_WAIT_DEFAULT;
return ( $this->hasPrimaryChanges()
|| $this->lastPrimaryChangeTimestamp() > microtime( true ) - $age );
}
public function pendingPrimaryChangeCallers() {
$fnames = [];
foreach ( $this->getOpenPrimaryConnections() as $conn ) {
$fnames = array_merge( $fnames, $conn->pendingWriteCallers() );
}
return $fnames;
}
public function explicitTrxActive() {
foreach ( $this->getOpenPrimaryConnections() as $conn ) {
if ( $conn->explicitTrxActive() ) {
return true;
}
}
return false;
}
private function setLaggedReplicaMode(): void {
$this->laggedReplicaMode = true;
$this->logger->warning( __METHOD__ . ": setting lagged replica mode" );
}
public function laggedReplicaUsed() {
return $this->laggedReplicaMode;
}
public function getReadOnlyReason( $domain = false ) {
if ( $this->readOnlyReason !== false ) {
return $this->readOnlyReason;
} elseif ( $this->isPrimaryRunningReadOnly() ) {
return 'The primary database server is running in read-only mode.';
}
return false;
}
/**
* @note This method suppresses DBError exceptions in order to avoid severe downtime
* @param IDatabase|null $conn Recently acquired primary connection; null if not applicable
* @return bool Whether the entire primary DB server or the local domain DB is read-only
*/
private function isPrimaryRunningReadOnly( IDatabase $conn = null ) {
// Context will often be HTTP GET/HEAD; heavily cache the results
return (bool)$this->wanCache->getWithSetCallback(
// Note that table prefixes are not related to server-side read-only mode
$this->wanCache->makeGlobalKey(
'rdbms-server-readonly',
$this->serverInfo->getPrimaryServerName()
),
self::TTL_CACHE_READONLY,
function ( $oldValue ) use ( $conn ) {
$scope = $this->trxProfiler->silenceForScope();
$conn ??= $this->getServerConnection(
ServerInfo::WRITER_INDEX,
self::DOMAIN_ANY,
self::CONN_SILENCE_ERRORS
);
if ( $conn ) {
try {
$value = (int)$conn->serverIsReadOnly();
} catch ( DBError $e ) {
$value = is_int( $oldValue ) ? $oldValue : 0;
}
} else {
$value = 0;
}
ScopedCallback::consume( $scope );
return $value;
},
[
'busyValue' => 0,
'pcTTL' => WANObjectCache::TTL_PROC_LONG
]
);
}
public function pingAll() {
$success = true;
foreach ( $this->getOpenConnections() as $conn ) {
if ( !$conn->ping() ) {
$success = false;
}
}
return $success;
}
/**
* Get all open connections
* @return \Generator|Database[]
*/
private function getOpenConnections() {
foreach ( $this->conns as $poolConnsByServer ) {
foreach ( $poolConnsByServer as $serverConns ) {
foreach ( $serverConns as $conn ) {
yield $conn;
}
}
}
}
/**
* Get all open primary connections
* @return \Generator|Database[]
*/
private function getOpenPrimaryConnections() {
foreach ( $this->conns as $poolConnsByServer ) {
/** @var IDatabase $conn */
foreach ( ( $poolConnsByServer[ServerInfo::WRITER_INDEX] ?? [] ) as $conn ) {
yield $conn;
}
}
}
public function getMaxLag() {
$host = '';
$maxLag = -1;
$maxIndex = 0;
if ( $this->serverInfo->hasReplicaServers() ) {
$lagTimes = $this->getLagTimes();
foreach ( $lagTimes as $i => $lag ) {
if ( $this->groupLoads[self::GROUP_GENERIC][$i] > 0 && $lag > $maxLag ) {
$maxLag = $lag;
$host = $this->serverInfo->getServerInfoStrict( $i, 'host' );
$maxIndex = $i;
}
}
}
return [ $host, $maxLag, $maxIndex ];
}
public function getLagTimes() {
if ( !$this->hasReplicaServers() ) {
return [ ServerInfo::WRITER_INDEX => 0 ]; // no replication = no lag
}
[ $indexesWithLag, $knownLagTimes ] = $this->serverInfo->getLagTimes();
return $this->loadMonitor->getLagTimes( $indexesWithLag ) + $knownLagTimes;
}
public function waitForPrimaryPos( IDatabase $conn ) {
if ( $conn->getLBInfo( self::INFO_SERVER_INDEX ) === ServerInfo::WRITER_INDEX ) {
return true; // not a replica DB server
}
// Get the current primary DB position, opening a connection only if needed
$flags = self::CONN_SILENCE_ERRORS;
$primaryConn = $this->getAnyOpenConnection( ServerInfo::WRITER_INDEX, $flags );
if ( $primaryConn ) {
$pos = $primaryConn->getPrimaryPos();
} else {
$primaryConn = $this->getServerConnection( ServerInfo::WRITER_INDEX, self::DOMAIN_ANY, $flags );
if ( !$primaryConn ) {
throw new DBReplicationWaitError(
null,
"Could not obtain a primary database connection to get the position"
);
}
$pos = $primaryConn->getPrimaryPos();
$this->closeConnection( $primaryConn );
}
if ( $pos instanceof DBPrimaryPos ) {
$this->logger->debug( __METHOD__ . ': waiting' );
$result = $conn->primaryPosWait( $pos, self::MAX_WAIT_DEFAULT );
$ok = ( $result !== null && $result != -1 );
if ( $ok ) {
$this->logger->debug( __METHOD__ . ': done waiting (success)' );
} else {
$this->logger->debug( __METHOD__ . ': done waiting (failure)' );
}
} else {
$ok = false; // something is misconfigured
$this->logger->error(
__METHOD__ . ': could not get primary pos for {db_server}',
$this->getConnLogContext( $conn, [ 'exception' => new RuntimeException() ] )
);
}
return $ok;
}
public function setTransactionListener( $name, callable $callback = null ) {
if ( $callback ) {
$this->trxRecurringCallbacks[$name] = $callback;
} else {
unset( $this->trxRecurringCallbacks[$name] );
}
foreach ( $this->getOpenPrimaryConnections() as $conn ) {
$conn->setTransactionListener( $name, $callback );
}
}
public function setTableAliases( array $aliases ) {
$this->tableAliases = $aliases;
}
public function setIndexAliases( array $aliases ) {
$this->indexAliases = $aliases;
}
public function setDomainAliases( array $aliases ) {
$this->domainAliases = $aliases;
}
public function setLocalDomainPrefix( $prefix ) {
$oldLocalDomain = $this->localDomain;
$this->localDomain = new DatabaseDomain(
$this->localDomain->getDatabase(),
$this->localDomain->getSchema(),
$prefix
);
// Update the prefix for existing connections.
// Existing DBConnRef handles will not be affected.
foreach ( $this->getOpenConnections() as $conn ) {
if ( $oldLocalDomain->equals( $conn->getDomainID() ) ) {
$conn->tablePrefix( $prefix );
}
}
}
public function redefineLocalDomain( $domain ) {
$this->closeAll( __METHOD__ );
$this->localDomain = DatabaseDomain::newFromId( $domain );
}
public function setTempTablesOnlyMode( $value, $domain ) {
$old = $this->tempTablesOnlyMode[$domain] ?? false;
if ( $value ) {
$this->tempTablesOnlyMode[$domain] = true;
} else {
unset( $this->tempTablesOnlyMode[$domain] );
}
return $old;
}
/**
* @param IDatabase $conn
* @return string Description of a connection handle for log messages
* @throws InvalidArgumentException
*/
private function stringifyConn( IDatabase $conn ) {
return $conn->getLBInfo( self::INFO_SERVER_INDEX ) . '/' . $conn->getDomainID();
}
/**
* @param int $flags A bitfield of flags
* @param int $bit Bit flag constant
* @return bool Whether the bit field has the specified bit flag set
*/
private function fieldHasBit( int $flags, int $bit ) {
return ( ( $flags & $bit ) === $bit );
}
/**
* Create a log context to pass to PSR-3 logger functions.
*
* @param IDatabase $conn
* @param array $extras Additional data to add to context
* @return array
*/
protected function getConnLogContext( IDatabase $conn, array $extras = [] ) {
return array_merge(
[
'db_server' => $conn->getServerName(),
'db_domain' => $conn->getDomainID()
],
$extras
);
}
}
/**
* @deprecated since 1.29
*/
class_alias( LoadBalancer::class, 'LoadBalancer' );