includes/cache/BacklinkCache.php
<?php
/**
* Class for fetching backlink lists, approximate backlink counts and
* partitions.
*
* 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
* @author Tim Starling
* @copyright © 2009, Tim Starling, Domas Mituzas
* @copyright © 2010, Max Sem
* @copyright © 2011, Antoine Musso
*/
namespace MediaWiki\Cache;
use Iterator;
use LogicException;
use MediaWiki\Config\ServiceOptions;
use MediaWiki\HookContainer\HookContainer;
use MediaWiki\HookContainer\HookRunner;
use MediaWiki\Linker\LinksMigration;
use MediaWiki\MainConfigNames;
use MediaWiki\Page\PageIdentity;
use MediaWiki\Page\PageIdentityValue;
use MediaWiki\Page\PageReference;
use MediaWiki\Title\Title;
use MediaWiki\Title\TitleValue;
use Psr\Log\LoggerInterface;
use RuntimeException;
use stdClass;
use WANObjectCache;
use Wikimedia\Rdbms\Database;
use Wikimedia\Rdbms\IConnectionProvider;
use Wikimedia\Rdbms\IReadableDatabase;
use Wikimedia\Rdbms\IResultWrapper;
use Wikimedia\Rdbms\SelectQueryBuilder;
/**
* Class for fetching backlink lists, approximate backlink counts and
* partitions. This is a shared cache.
*
* Instances of this class should typically be fetched with the method
* ::getBacklinkCache() from the BacklinkCacheFactory service.
*
* Ideally you should only get your backlinks from here when you think
* there is some advantage in caching them. Otherwise, it's just a waste
* of memory.
*/
class BacklinkCache {
/**
* @internal Used by ServiceWiring.php
*/
public const CONSTRUCTOR_OPTIONS = [
MainConfigNames::UpdateRowsPerJob,
];
/**
* Multi-dimensional array representing batches. Keys are:
* > (string) links table name
* > (int) batch size
* > 'numRows' : Number of rows for this link table
* > 'batches' : [ [ $start, $end ] ]
*
* @see BacklinkCache::partitionResult()
* @var array[]
*/
private $partitionCache = [];
/**
* Contains the whole links from a database result.
* This is raw data that will be partitioned in $partitionCache
*
* Initialized with BacklinkCache::queryLinks()
*
* @var IResultWrapper[]
*/
private $fullResultCache = [];
/**
* Cache for hasLinks()
*
* @var bool[]
*/
private $hasLinksCache = [];
/** @var WANObjectCache */
private $wanCache;
/** @var HookRunner */
private $hookRunner;
/**
* Local copy of a PageReference object
* @var PageReference
*/
private $page;
private const CACHE_EXPIRY = 3600;
private IConnectionProvider $dbProvider;
private ServiceOptions $options;
private LinksMigration $linksMigration;
private LoggerInterface $logger;
/**
* Create a new BacklinkCache
*
* @param ServiceOptions $options
* @param LinksMigration $linksMigration
* @param WANObjectCache $wanCache
* @param HookContainer $hookContainer
* @param IConnectionProvider $dbProvider
* @param LoggerInterface $logger
* @param PageReference $page Page to create a backlink cache for
*/
public function __construct(
ServiceOptions $options,
LinksMigration $linksMigration,
WANObjectCache $wanCache,
HookContainer $hookContainer,
IConnectionProvider $dbProvider,
LoggerInterface $logger,
PageReference $page
) {
$options->assertRequiredOptions( self::CONSTRUCTOR_OPTIONS );
$this->options = $options;
$this->linksMigration = $linksMigration;
$this->wanCache = $wanCache;
$this->hookRunner = new HookRunner( $hookContainer );
$this->dbProvider = $dbProvider;
$this->logger = $logger;
$this->page = $page;
}
/**
* @since 1.37
* @return PageReference
*/
public function getPage(): PageReference {
return $this->page;
}
/**
* Get the replica DB connection to the database
*
* @return IReadableDatabase
*/
private function getDB() {
return $this->dbProvider->getReplicaDatabase();
}
/**
* Get the backlinks for a given table. Cached in process memory only.
* @param string $table
* @param int|bool $startId
* @param int|bool $endId
* @param int|float $max Integer, or INF for no max
* @return Iterator<PageIdentity>
* @since 1.37
*/
public function getLinkPages(
string $table, $startId = false, $endId = false, $max = INF
): Iterator {
$i = 0;
foreach ( $this->queryLinks( $table, $startId, $endId, $max ) as $row ) {
yield PageIdentityValue::localIdentity(
$row->page_id, $row->page_namespace, $row->page_title );
// queryLinks() may return too many rows
if ( is_finite( $max ) && ++$i >= $max ) {
break;
}
}
}
/**
* Get the backlinks for a given table. Cached in process memory only.
*
* @param string $table
* @param int|bool $startId
* @param int|bool $endId
* @param int|float $max A hint for the maximum number of rows to return.
* May return more rows if there is a previously cached result set.
* @param string $select 'all' or 'ids'
* @return IResultWrapper
*/
private function queryLinks( $table, $startId, $endId, $max, $select = 'all' ) {
if ( !$startId && !$endId && isset( $this->fullResultCache[$table] ) ) {
$this->logger->debug( __METHOD__ . ': got results from cache' );
return $this->fullResultCache[$table];
}
$this->logger->debug( __METHOD__ . ': got results from DB' );
$queryBuilder = $this->initQueryBuilderForTable( $table, $select );
$fromField = $this->getPrefix( $table ) . '_from';
// Use the from field in the condition rather than the joined page_id,
// because databases are stupid and don't necessarily propagate indexes.
if ( $startId ) {
$queryBuilder->where(
$this->getDB()->expr( $fromField, '>=', $startId )
);
}
if ( $endId ) {
$queryBuilder->where(
$this->getDB()->expr( $fromField, '<=', $endId )
);
}
$queryBuilder->orderBy( $fromField );
if ( is_finite( $max ) && $max > 0 ) {
$queryBuilder->limit( $max );
}
$res = $queryBuilder->caller( __METHOD__ )->fetchResultSet();
if ( $select === 'all' && !$startId && !$endId && $res->numRows() < $max ) {
// The full results fit within the limit, so cache them
$this->fullResultCache[$table] = $res;
} else {
$this->logger->debug( __METHOD__ . ": results from DB were uncacheable" );
}
return $res;
}
/**
* Get the field name prefix for a given table
* @param string $table
* @return null|string
*/
private function getPrefix( $table ) {
static $prefixes = [
'pagelinks' => 'pl',
'imagelinks' => 'il',
'categorylinks' => 'cl',
'templatelinks' => 'tl',
'redirect' => 'rd',
];
if ( isset( $prefixes[$table] ) ) {
return $prefixes[$table];
} else {
$prefix = null;
$this->hookRunner->onBacklinkCacheGetPrefix( $table, $prefix );
if ( $prefix ) {
return $prefix;
} else {
throw new LogicException( "Invalid table \"$table\" in " . __CLASS__ );
}
}
}
/**
* Initialize a new SelectQueryBuilder for selecting backlinks,
* with a join on the page table if needed.
*
* @param string $table
* @param string $select
* @return SelectQueryBuilder
*/
private function initQueryBuilderForTable( string $table, string $select ): SelectQueryBuilder {
$prefix = $this->getPrefix( $table );
$queryBuilder = $this->getDB()->newSelectQueryBuilder();
$joinPageTable = $select !== 'ids';
if ( $select === 'ids' ) {
$queryBuilder->select( [ 'page_id' => $prefix . '_from' ] );
} else {
$queryBuilder->select( [ 'page_namespace', 'page_title', 'page_id' ] );
}
$queryBuilder->from( $table );
/*
* If the table is one of the tables known to this method,
* we can use a nice join() method later, always joining on page_id={$prefix}_from.
* If the table is unknown here, and only supported via a hook,
* the hook only produces a single $conds array,
* so we have to use a traditional / ANSI-89 JOIN,
* with the page table just added to the list of tables and the join conds in the WHERE part.
*/
$knownTable = true;
switch ( $table ) {
case 'pagelinks':
case 'templatelinks':
$queryBuilder->where(
$this->linksMigration->getLinksConditions( $table, TitleValue::newFromPage( $this->page ) )
);
break;
case 'redirect':
$queryBuilder->where( [
"{$prefix}_namespace" => $this->page->getNamespace(),
"{$prefix}_title" => $this->page->getDBkey(),
"{$prefix}_interwiki" => [ '', null ],
] );
break;
case 'imagelinks':
case 'categorylinks':
$queryBuilder->where( [
"{$prefix}_to" => $this->page->getDBkey(),
] );
break;
default:
$knownTable = false;
$conds = null;
$this->hookRunner->onBacklinkCacheGetConditions( $table,
Title::newFromPageReference( $this->page ),
$conds
);
if ( !$conds ) {
throw new LogicException( "Invalid table \"$table\" in " . __CLASS__ );
}
if ( $joinPageTable ) {
$queryBuilder->table( 'page' ); // join condition in $conds
} else {
// remove any page_id condition from $conds
$conds = array_filter( (array)$conds, static function ( $clause ) { // kind of janky
return !preg_match( '/(\b|=)page_id(\b|=)/', (string)$clause );
} );
}
$queryBuilder->where( $conds );
break;
}
if ( $knownTable && $joinPageTable ) {
$queryBuilder->join( 'page', null, "page_id={$prefix}_from" );
}
if ( $joinPageTable ) {
$queryBuilder->straightJoinOption();
}
return $queryBuilder;
}
/**
* Check if there are any backlinks. Only use the process cache, since the
* WAN cache is potentially stale (T368006).
*
* @param string $table
* @return bool
*/
public function hasLinks( $table ) {
if ( isset( $this->hasLinksCache[$table] ) ) {
return $this->hasLinksCache[$table];
}
if ( isset( $this->partitionCache[$table] ) ) {
$entry = reset( $this->partitionCache[$table] );
return (bool)$entry['numRows'];
}
if ( isset( $this->fullResultCache[$table] ) ) {
return (bool)$this->fullResultCache[$table]->numRows();
}
$hasLinks = (bool)$this->queryLinks( $table, false, false, 1 )->numRows();
$this->hasLinksCache[$table] = $hasLinks;
return $hasLinks;
}
/**
* Get the approximate number of backlinks
* @param string $table
* @return int
*/
public function getNumLinks( $table ) {
if ( isset( $this->partitionCache[$table] ) ) {
$entry = reset( $this->partitionCache[$table] );
return $entry['numRows'];
}
if ( isset( $this->fullResultCache[$table] ) ) {
return $this->fullResultCache[$table]->numRows();
}
return $this->wanCache->getWithSetCallback(
$this->wanCache->makeKey(
'numbacklinks',
CacheKeyHelper::getKeyForPage( $this->page ),
$table
),
self::CACHE_EXPIRY,
function ( $oldValue, &$ttl, array &$setOpts ) use ( $table ) {
$setOpts += Database::getCacheSetOptions( $this->getDB() );
// Use partition() since it will batch the query and skip the JOIN.
// Use $wgUpdateRowsPerJob just to encourage cache reuse for jobs.
$batchSize = $this->options->get( MainConfigNames::UpdateRowsPerJob );
$this->partition( $table, $batchSize );
return $this->partitionCache[$table][$batchSize]['numRows'];
}
);
}
/**
* Partition the backlinks into batches.
* Returns an array giving the start and end of each range. The first
* batch has a start of false, and the last batch has an end of false.
*
* @param string $table The links table name
* @param int $batchSize
* @return array
*/
public function partition( $table, $batchSize ) {
if ( isset( $this->partitionCache[$table][$batchSize] ) ) {
$this->logger->debug( __METHOD__ . ": got from partition cache" );
return $this->partitionCache[$table][$batchSize]['batches'];
}
$this->partitionCache[$table][$batchSize] = false;
$cacheEntry =& $this->partitionCache[$table][$batchSize];
if ( isset( $this->fullResultCache[$table] ) ) {
$res = $this->fullResultCache[$table];
$numRows = $res->numRows();
$batches = $this->partitionResult( $res, $numRows, $batchSize );
$this->openBatchEnds( $batches );
$cacheEntry = [ 'numRows' => $numRows, 'batches' => $batches ];
$this->logger->debug( __METHOD__ . ": got from full result cache" );
return $cacheEntry['batches'];
}
$cacheEntry = $this->wanCache->getWithSetCallback(
$this->wanCache->makeKey(
'backlinks',
CacheKeyHelper::getKeyForPage( $this->page ),
$table,
$batchSize
),
self::CACHE_EXPIRY,
function ( $oldValue, &$ttl, array &$setOpts ) use ( $table, $batchSize ) {
$setOpts += Database::getCacheSetOptions( $this->getDB() );
$value = [ 'numRows' => 0, 'batches' => [] ];
// Do the selects in batches to avoid client-side OOMs (T45452).
// Use a LIMIT that plays well with $batchSize to keep equal sized partitions.
$selectSize = max( $batchSize, 200_000 - ( 200_000 % $batchSize ) );
$start = false;
do {
$res = $this->queryLinks( $table, $start, false, $selectSize, 'ids' );
$numRows = $res->numRows();
$batches = $this->partitionResult( $res, $numRows, $batchSize );
// Merge the link count and range partitions for this chunk
$value['numRows'] += $numRows;
$value['batches'] = array_merge( $value['batches'], $batches );
if ( count( $batches ) ) {
// pick up after this inclusive range
$start = end( $batches )[1] + 1;
}
} while ( $numRows >= $selectSize );
// Make sure the first range has start=false and the last one has end=false
$this->openBatchEnds( $value['batches'] );
return $value;
}
);
return $cacheEntry['batches'];
}
/**
* Modify an array of batches, setting the start of the first batch to
* false, and the end of the last batch to false, so that the complete
* set of batches covers the entire ID range from 0 to infinity.
*
* @param array &$batches
*/
private function openBatchEnds( array &$batches ) {
if ( !count( $batches ) ) {
$batches = [ [ false, false ] ];
} else {
$batches[0][0] = false;
$batches[ array_key_last( $batches ) ][1] = false;
}
}
/**
* Partition a DB result with backlinks in it into batches
* @param IResultWrapper $res Database result
* @param int $numRows The number of rows to use from the result set
* @param int $batchSize
* @return int[][]
*/
private function partitionResult( $res, $numRows, $batchSize ) {
$numBatches = ceil( $numRows / $batchSize );
$batches = [];
for ( $i = 0; $i < $numBatches; $i++ ) {
$rowNum = $i * $batchSize;
$res->seek( $rowNum );
$row = $res->fetchObject();
$start = (int)$row->page_id;
$rowNum = min( $numRows - 1, ( $i + 1 ) * $batchSize - 1 );
$res->seek( $rowNum );
$row = $res->fetchObject();
$end = (int)$row->page_id;
// Check order
if ( $start && $end && $start > $end ) {
throw new RuntimeException( __METHOD__ . ': Internal error: query result out of order' );
}
$batches[] = [ $start, $end ];
}
return $batches;
}
/**
* Get a PageIdentity iterator for cascade-protected template/file use backlinks
*
* @return Iterator<PageIdentity>
* @since 1.37
*/
public function getCascadeProtectedLinkPages(): Iterator {
foreach ( $this->getCascadeProtectedLinksInternal() as $row ) {
yield PageIdentityValue::localIdentity(
$row->page_id, $row->page_namespace, $row->page_title );
}
}
/**
* Get an array of cascade-protected template/file use backlinks
*
* @return stdClass[]
*/
private function getCascadeProtectedLinksInternal(): array {
$dbr = $this->getDB();
// @todo: use UNION without breaking tests that use temp tables
$resSets = [];
$linkConds = $this->linksMigration->getLinksConditions(
'templatelinks', TitleValue::newFromPage( $this->page )
);
$resSets[] = $dbr->newSelectQueryBuilder()
->select( [ 'page_namespace', 'page_title', 'page_id' ] )
->from( 'templatelinks' )
->join( 'page_restrictions', null, 'tl_from = pr_page' )
->join( 'page', null, 'page_id = tl_from' )
->where( $linkConds )
->andWhere( [ 'pr_cascade' => 1 ] )
->distinct()
->caller( __METHOD__ )->fetchResultSet();
if ( $this->page->getNamespace() === NS_FILE ) {
$resSets[] = $dbr->newSelectQueryBuilder()
->select( [ 'page_namespace', 'page_title', 'page_id' ] )
->from( 'imagelinks' )
->join( 'page_restrictions', null, 'il_from = pr_page' )
->join( 'page', null, 'page_id = il_from' )
->where( [
'il_to' => $this->page->getDBkey(),
'pr_cascade' => 1,
] )
->distinct()
->caller( __METHOD__ )->fetchResultSet();
}
// Combine and de-duplicate the results
$mergedRes = [];
foreach ( $resSets as $res ) {
foreach ( $res as $row ) {
// Index by page_id to remove duplicates
$mergedRes[$row->page_id] = $row;
}
}
// Now that we've de-duplicated, throw away the keys
return array_values( $mergedRes );
}
}
/** @deprecated class alias since 1.42 */
class_alias( BacklinkCache::class, 'BacklinkCache' );