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diff --git a/www/wiki/includes/cache/BacklinkCache.php b/www/wiki/includes/cache/BacklinkCache.php
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+<?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
+ */
+
+use Wikimedia\Rdbms\ResultWrapper;
+use Wikimedia\Rdbms\FakeResultWrapper;
+use Wikimedia\Rdbms\IDatabase;
+use MediaWiki\MediaWikiServices;
+
+/**
+ * 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
+ * $title->getBacklinkCache().
+ *
+ * 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.
+ *
+ * Introduced by r47317
+ */
+class BacklinkCache {
+	/** @var BacklinkCache */
+	protected static $instance;
+
+	/**
+	 * Multi dimensions 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()
+	 *
+	 * Cleared with BacklinkCache::clear()
+	 * @var array[]
+	 */
+	protected $partitionCache = [];
+
+	/**
+	 * Contains the whole links from a database result.
+	 * This is raw data that will be partitioned in $partitionCache
+	 *
+	 * Initialized with BacklinkCache::getLinks()
+	 * Cleared with BacklinkCache::clear()
+	 * @var ResultWrapper[]
+	 */
+	protected $fullResultCache = [];
+
+	/**
+	 * @var WANObjectCache
+	 */
+	protected $wanCache;
+
+	/**
+	 * Local copy of a database object.
+	 *
+	 * Accessor: BacklinkCache::getDB()
+	 * Mutator : BacklinkCache::setDB()
+	 * Cleared with BacklinkCache::clear()
+	 */
+	protected $db;
+
+	/**
+	 * Local copy of a Title object
+	 */
+	protected $title;
+
+	const CACHE_EXPIRY = 3600;
+
+	/**
+	 * Create a new BacklinkCache
+	 *
+	 * @param Title $title : Title object to create a backlink cache for
+	 */
+	public function __construct( Title $title ) {
+		$this->title = $title;
+		$this->wanCache = MediaWikiServices::getInstance()->getMainWANObjectCache();
+	}
+
+	/**
+	 * Create a new BacklinkCache or reuse any existing one.
+	 * Currently, only one cache instance can exist; callers that
+	 * need multiple backlink cache objects should keep them in scope.
+	 *
+	 * @param Title $title Title object to get a backlink cache for
+	 * @return BacklinkCache
+	 */
+	public static function get( Title $title ) {
+		if ( !self::$instance || !self::$instance->title->equals( $title ) ) {
+			self::$instance = new self( $title );
+		}
+		return self::$instance;
+	}
+
+	/**
+	 * Serialization handler, diasallows to serialize the database to prevent
+	 * failures after this class is deserialized from cache with dead DB
+	 * connection.
+	 *
+	 * @return array
+	 */
+	function __sleep() {
+		return [ 'partitionCache', 'fullResultCache', 'title' ];
+	}
+
+	/**
+	 * Clear locally stored data and database object. Invalidate data in memcache.
+	 */
+	public function clear() {
+		$this->partitionCache = [];
+		$this->fullResultCache = [];
+		$this->wanCache->touchCheckKey( $this->makeCheckKey() );
+		unset( $this->db );
+	}
+
+	/**
+	 * Set the Database object to use
+	 *
+	 * @param IDatabase $db
+	 */
+	public function setDB( $db ) {
+		$this->db = $db;
+	}
+
+	/**
+	 * Get the replica DB connection to the database
+	 * When non existing, will initialize the connection.
+	 * @return IDatabase
+	 */
+	protected function getDB() {
+		if ( !isset( $this->db ) ) {
+			$this->db = wfGetDB( DB_REPLICA );
+		}
+
+		return $this->db;
+	}
+
+	/**
+	 * 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 $max
+	 * @return TitleArrayFromResult
+	 */
+	public function getLinks( $table, $startId = false, $endId = false, $max = INF ) {
+		return TitleArray::newFromResult( $this->queryLinks( $table, $startId, $endId, $max ) );
+	}
+
+	/**
+	 * 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 $max
+	 * @param string $select 'all' or 'ids'
+	 * @return ResultWrapper
+	 */
+	protected function queryLinks( $table, $startId, $endId, $max, $select = 'all' ) {
+		$fromField = $this->getPrefix( $table ) . '_from';
+
+		if ( !$startId && !$endId && is_infinite( $max )
+			&& isset( $this->fullResultCache[$table] )
+		) {
+			wfDebug( __METHOD__ . ": got results from cache\n" );
+			$res = $this->fullResultCache[$table];
+		} else {
+			wfDebug( __METHOD__ . ": got results from DB\n" );
+			$conds = $this->getConditions( $table );
+			// 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 ) {
+				$conds[] = "$fromField >= " . intval( $startId );
+			}
+			if ( $endId ) {
+				$conds[] = "$fromField <= " . intval( $endId );
+			}
+			$options = [ 'ORDER BY' => $fromField ];
+			if ( is_finite( $max ) && $max > 0 ) {
+				$options['LIMIT'] = $max;
+			}
+
+			if ( $select === 'ids' ) {
+				// Just select from the backlink table and ignore the page JOIN
+				$res = $this->getDB()->select(
+					$table,
+					[ $this->getPrefix( $table ) . '_from AS page_id' ],
+					array_filter( $conds, function ( $clause ) { // kind of janky
+						return !preg_match( '/(\b|=)page_id(\b|=)/', $clause );
+					} ),
+					__METHOD__,
+					$options
+				);
+			} else {
+				// Select from the backlink table and JOIN with page title information
+				$res = $this->getDB()->select(
+					[ $table, 'page' ],
+					[ 'page_namespace', 'page_title', 'page_id' ],
+					$conds,
+					__METHOD__,
+					array_merge( [ 'STRAIGHT_JOIN' ], $options )
+				);
+			}
+
+			if ( $select === 'all' && !$startId && !$endId && $res->numRows() < $max ) {
+				// The full results fit within the limit, so cache them
+				$this->fullResultCache[$table] = $res;
+			} else {
+				wfDebug( __METHOD__ . ": results from DB were uncacheable\n" );
+			}
+		}
+
+		return $res;
+	}
+
+	/**
+	 * Get the field name prefix for a given table
+	 * @param string $table
+	 * @throws MWException
+	 * @return null|string
+	 */
+	protected 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;
+			Hooks::run( 'BacklinkCacheGetPrefix', [ $table, &$prefix ] );
+			if ( $prefix ) {
+				return $prefix;
+			} else {
+				throw new MWException( "Invalid table \"$table\" in " . __CLASS__ );
+			}
+		}
+	}
+
+	/**
+	 * Get the SQL condition array for selecting backlinks, with a join
+	 * on the page table.
+	 * @param string $table
+	 * @throws MWException
+	 * @return array|null
+	 */
+	protected function getConditions( $table ) {
+		$prefix = $this->getPrefix( $table );
+
+		switch ( $table ) {
+			case 'pagelinks':
+			case 'templatelinks':
+				$conds = [
+					"{$prefix}_namespace" => $this->title->getNamespace(),
+					"{$prefix}_title" => $this->title->getDBkey(),
+					"page_id={$prefix}_from"
+				];
+				break;
+			case 'redirect':
+				$conds = [
+					"{$prefix}_namespace" => $this->title->getNamespace(),
+					"{$prefix}_title" => $this->title->getDBkey(),
+					$this->getDB()->makeList( [
+						"{$prefix}_interwiki" => '',
+						"{$prefix}_interwiki IS NULL",
+					], LIST_OR ),
+					"page_id={$prefix}_from"
+				];
+				break;
+			case 'imagelinks':
+			case 'categorylinks':
+				$conds = [
+					"{$prefix}_to" => $this->title->getDBkey(),
+					"page_id={$prefix}_from"
+				];
+				break;
+			default:
+				$conds = null;
+				Hooks::run( 'BacklinkCacheGetConditions', [ $table, $this->title, &$conds ] );
+				if ( !$conds ) {
+					throw new MWException( "Invalid table \"$table\" in " . __CLASS__ );
+				}
+		}
+
+		return $conds;
+	}
+
+	/**
+	 * Check if there are any backlinks
+	 * @param string $table
+	 * @return bool
+	 */
+	public function hasLinks( $table ) {
+		return ( $this->getNumLinks( $table, 1 ) > 0 );
+	}
+
+	/**
+	 * Get the approximate number of backlinks
+	 * @param string $table
+	 * @param int $max Only count up to this many backlinks
+	 * @return int
+	 */
+	public function getNumLinks( $table, $max = INF ) {
+		global $wgUpdateRowsPerJob;
+
+		// 1) try partition cache ...
+		if ( isset( $this->partitionCache[$table] ) ) {
+			$entry = reset( $this->partitionCache[$table] );
+
+			return min( $max, $entry['numRows'] );
+		}
+
+		// 2) ... then try full result cache ...
+		if ( isset( $this->fullResultCache[$table] ) ) {
+			return min( $max, $this->fullResultCache[$table]->numRows() );
+		}
+
+		$memcKey = $this->wanCache->makeKey(
+			'numbacklinks',
+			md5( $this->title->getPrefixedDBkey() ),
+			$table
+		);
+
+		// 3) ... fallback to memcached ...
+		$curTTL = INF;
+		$count = $this->wanCache->get(
+			$memcKey,
+			$curTTL,
+			[
+				$this->makeCheckKey()
+			]
+		);
+		if ( $count && ( $curTTL > 0 ) ) {
+			return min( $max, $count );
+		}
+
+		// 4) fetch from the database ...
+		if ( is_infinite( $max ) ) { // no limit at all
+			// Use partition() since it will batch the query and skip the JOIN.
+			// Use $wgUpdateRowsPerJob just to encourage cache reuse for jobs.
+			$this->partition( $table, $wgUpdateRowsPerJob ); // updates $this->partitionCache
+			return $this->partitionCache[$table][$wgUpdateRowsPerJob]['numRows'];
+		} else { // probably some sane limit
+			// Fetch the full title info, since the caller will likely need it next
+			$count = $this->getLinks( $table, false, false, $max )->count();
+			if ( $count < $max ) { // full count
+				$this->wanCache->set( $memcKey, $count, self::CACHE_EXPIRY );
+			}
+		}
+
+		return min( $max, $count );
+	}
+
+	/**
+	 * 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 ) {
+		// 1) try partition cache ...
+		if ( isset( $this->partitionCache[$table][$batchSize] ) ) {
+			wfDebug( __METHOD__ . ": got from partition cache\n" );
+
+			return $this->partitionCache[$table][$batchSize]['batches'];
+		}
+
+		$this->partitionCache[$table][$batchSize] = false;
+		$cacheEntry =& $this->partitionCache[$table][$batchSize];
+
+		// 2) ... then try full result cache ...
+		if ( isset( $this->fullResultCache[$table] ) ) {
+			$cacheEntry = $this->partitionResult( $this->fullResultCache[$table], $batchSize );
+			wfDebug( __METHOD__ . ": got from full result cache\n" );
+
+			return $cacheEntry['batches'];
+		}
+
+		$memcKey = $this->wanCache->makeKey(
+			'backlinks',
+			md5( $this->title->getPrefixedDBkey() ),
+			$table,
+			$batchSize
+		);
+
+		// 3) ... fallback to memcached ...
+		$curTTL = 0;
+		$memcValue = $this->wanCache->get(
+			$memcKey,
+			$curTTL,
+			[
+				$this->makeCheckKey()
+			]
+		);
+		if ( is_array( $memcValue ) && ( $curTTL > 0 ) ) {
+			$cacheEntry = $memcValue;
+			wfDebug( __METHOD__ . ": got from memcached $memcKey\n" );
+
+			return $cacheEntry['batches'];
+		}
+
+		// 4) ... finally fetch from the slow database :(
+		$cacheEntry = [ 'numRows' => 0, 'batches' => [] ]; // final result
+		// 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, 200000 - ( 200000 % $batchSize ) );
+		$start = false;
+		do {
+			$res = $this->queryLinks( $table, $start, false, $selectSize, 'ids' );
+			$partitions = $this->partitionResult( $res, $batchSize, false );
+			// Merge the link count and range partitions for this chunk
+			$cacheEntry['numRows'] += $partitions['numRows'];
+			$cacheEntry['batches'] = array_merge( $cacheEntry['batches'], $partitions['batches'] );
+			if ( count( $partitions['batches'] ) ) {
+				list( , $lEnd ) = end( $partitions['batches'] );
+				$start = $lEnd + 1; // pick up after this inclusive range
+			}
+		} while ( $partitions['numRows'] >= $selectSize );
+		// Make sure the first range has start=false and the last one has end=false
+		if ( count( $cacheEntry['batches'] ) ) {
+			$cacheEntry['batches'][0][0] = false;
+			$cacheEntry['batches'][count( $cacheEntry['batches'] ) - 1][1] = false;
+		}
+
+		// Save partitions to memcached
+		$this->wanCache->set( $memcKey, $cacheEntry, self::CACHE_EXPIRY );
+
+		// Save backlink count to memcached
+		$memcKey = $this->wanCache->makeKey(
+			'numbacklinks',
+			md5( $this->title->getPrefixedDBkey() ),
+			$table
+		);
+		$this->wanCache->set( $memcKey, $cacheEntry['numRows'], self::CACHE_EXPIRY );
+
+		wfDebug( __METHOD__ . ": got from database\n" );
+
+		return $cacheEntry['batches'];
+	}
+
+	/**
+	 * Partition a DB result with backlinks in it into batches
+	 * @param ResultWrapper $res Database result
+	 * @param int $batchSize
+	 * @param bool $isComplete Whether $res includes all the backlinks
+	 * @throws MWException
+	 * @return array
+	 */
+	protected function partitionResult( $res, $batchSize, $isComplete = true ) {
+		$batches = [];
+		$numRows = $res->numRows();
+		$numBatches = ceil( $numRows / $batchSize );
+
+		for ( $i = 0; $i < $numBatches; $i++ ) {
+			if ( $i == 0 && $isComplete ) {
+				$start = false;
+			} else {
+				$rowNum = $i * $batchSize;
+				$res->seek( $rowNum );
+				$row = $res->fetchObject();
+				$start = (int)$row->page_id;
+			}
+
+			if ( $i == ( $numBatches - 1 ) && $isComplete ) {
+				$end = false;
+			} else {
+				$rowNum = min( $numRows - 1, ( $i + 1 ) * $batchSize - 1 );
+				$res->seek( $rowNum );
+				$row = $res->fetchObject();
+				$end = (int)$row->page_id;
+			}
+
+			# Sanity check order
+			if ( $start && $end && $start > $end ) {
+				throw new MWException( __METHOD__ . ': Internal error: query result out of order' );
+			}
+
+			$batches[] = [ $start, $end ];
+		}
+
+		return [ 'numRows' => $numRows, 'batches' => $batches ];
+	}
+
+	/**
+	 * Get a Title iterator for cascade-protected template/file use backlinks
+	 *
+	 * @return TitleArray
+	 * @since 1.25
+	 */
+	public function getCascadeProtectedLinks() {
+		$dbr = $this->getDB();
+
+		// @todo: use UNION without breaking tests that use temp tables
+		$resSets = [];
+		$resSets[] = $dbr->select(
+			[ 'templatelinks', 'page_restrictions', 'page' ],
+			[ 'page_namespace', 'page_title', 'page_id' ],
+			[
+				'tl_namespace' => $this->title->getNamespace(),
+				'tl_title' => $this->title->getDBkey(),
+				'tl_from = pr_page',
+				'pr_cascade' => 1,
+				'page_id = tl_from'
+			],
+			__METHOD__,
+			[ 'DISTINCT' ]
+		);
+		if ( $this->title->getNamespace() == NS_FILE ) {
+			$resSets[] = $dbr->select(
+				[ 'imagelinks', 'page_restrictions', 'page' ],
+				[ 'page_namespace', 'page_title', 'page_id' ],
+				[
+					'il_to' => $this->title->getDBkey(),
+					'il_from = pr_page',
+					'pr_cascade' => 1,
+					'page_id = il_from'
+				],
+				__METHOD__,
+				[ 'DISTINCT' ]
+			);
+		}
+
+		// Combine and de-duplicate the results
+		$mergedRes = [];
+		foreach ( $resSets as $res ) {
+			foreach ( $res as $row ) {
+				$mergedRes[$row->page_id] = $row;
+			}
+		}
+
+		return TitleArray::newFromResult(
+			new FakeResultWrapper( array_values( $mergedRes ) ) );
+	}
+
+	/**
+	 * Returns check key for the backlinks cache for a particular title
+	 *
+	 * @return String
+	 */
+	private function makeCheckKey() {
+		return $this->wanCache->makeKey(
+			'backlinks',
+			md5( $this->title->getPrefixedDBkey() )
+		);
+	}
+}