420 lines
11 KiB
PHP
420 lines
11 KiB
PHP
<?php
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/**
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* Class for fetching backlink lists, approximate backlink counts and
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* partitions.
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License along
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* with this program; if not, write to the Free Software Foundation, Inc.,
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* 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
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* http://www.gnu.org/copyleft/gpl.html
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*
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* @file
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* @author Tim Starling
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* @copyright © 2009, Tim Starling, Domas Mituzas
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* @copyright © 2010, Max Sem
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* @copyright © 2011, Antoine Musso
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*/
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/**
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* Class for fetching backlink lists, approximate backlink counts and
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* partitions. This is a shared cache.
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*
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* Instances of this class should typically be fetched with the method
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* $title->getBacklinkCache().
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*
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* Ideally you should only get your backlinks from here when you think
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* there is some advantage in caching them. Otherwise it's just a waste
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* of memory.
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*
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* Introduced by r47317
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*
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* @internal documentation reviewed on 18 Mar 2011 by hashar
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*/
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class BacklinkCache {
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/** @var ProcessCacheLRU */
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protected static $cache;
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/**
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* Multi dimensions array representing batches. Keys are:
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* > (string) links table name
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* > 'numRows' : Number of rows for this link table
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* > 'batches' : array( $start, $end )
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*
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* @see BacklinkCache::partitionResult()
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*
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* Cleared with BacklinkCache::clear()
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*/
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protected $partitionCache = array();
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/**
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* Contains the whole links from a database result.
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* This is raw data that will be partitioned in $partitionCache
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*
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* Initialized with BacklinkCache::getLinks()
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* Cleared with BacklinkCache::clear()
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*/
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protected $fullResultCache = array();
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/**
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* Local copy of a database object.
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*
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* Accessor: BacklinkCache::getDB()
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* Mutator : BacklinkCache::setDB()
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* Cleared with BacklinkCache::clear()
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*/
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protected $db;
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/**
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* Local copy of a Title object
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*/
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protected $title;
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const CACHE_EXPIRY = 3600;
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/**
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* Create a new BacklinkCache
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*
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* @param Title $title : Title object to create a backlink cache for
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*/
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public function __construct( Title $title ) {
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$this->title = $title;
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}
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/**
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* Create a new BacklinkCache or reuse any existing one.
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* Currently, only one cache instance can exist; callers that
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* need multiple backlink cache objects should keep them in scope.
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*
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* @param Title $title : Title object to get a backlink cache for
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* @return BacklinkCache
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*/
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public static function get( Title $title ) {
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if ( !self::$cache ) { // init cache
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self::$cache = new ProcessCacheLRU( 1 );
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}
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$dbKey = $title->getPrefixedDBkey();
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if ( !self::$cache->has( $dbKey, 'obj' ) ) {
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self::$cache->set( $dbKey, 'obj', new self( $title ) );
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}
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return self::$cache->get( $dbKey, 'obj' );
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}
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/**
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* Serialization handler, diasallows to serialize the database to prevent
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* failures after this class is deserialized from cache with dead DB
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* connection.
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*
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* @return array
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*/
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function __sleep() {
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return array( 'partitionCache', 'fullResultCache', 'title' );
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}
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/**
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* Clear locally stored data and database object.
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*/
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public function clear() {
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$this->partitionCache = array();
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$this->fullResultCache = array();
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unset( $this->db );
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}
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/**
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* Set the Database object to use
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*
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* @param $db DatabaseBase
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*/
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public function setDB( $db ) {
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$this->db = $db;
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}
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/**
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* Get the slave connection to the database
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* When non existing, will initialize the connection.
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* @return DatabaseBase object
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*/
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protected function getDB() {
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if ( !isset( $this->db ) ) {
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$this->db = wfGetDB( DB_SLAVE );
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}
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return $this->db;
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}
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/**
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* Get the backlinks for a given table. Cached in process memory only.
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* @param $table String
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* @param $startId Integer or false
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* @param $endId Integer or false
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* @return TitleArrayFromResult
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*/
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public function getLinks( $table, $startId = false, $endId = false ) {
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wfProfileIn( __METHOD__ );
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$fromField = $this->getPrefix( $table ) . '_from';
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if ( $startId || $endId ) {
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// Partial range, not cached
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wfDebug( __METHOD__ . ": from DB (uncacheable range)\n" );
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$conds = $this->getConditions( $table );
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// Use the from field in the condition rather than the joined page_id,
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// because databases are stupid and don't necessarily propagate indexes.
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if ( $startId ) {
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$conds[] = "$fromField >= " . intval( $startId );
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}
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if ( $endId ) {
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$conds[] = "$fromField <= " . intval( $endId );
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}
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$res = $this->getDB()->select(
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array( $table, 'page' ),
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array( 'page_namespace', 'page_title', 'page_id' ),
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$conds,
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__METHOD__,
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array(
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'STRAIGHT_JOIN',
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'ORDER BY' => $fromField
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) );
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$ta = TitleArray::newFromResult( $res );
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wfProfileOut( __METHOD__ );
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return $ta;
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}
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// @todo FIXME: Make this a function?
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if ( !isset( $this->fullResultCache[$table] ) ) {
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wfDebug( __METHOD__ . ": from DB\n" );
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$res = $this->getDB()->select(
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array( $table, 'page' ),
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array( 'page_namespace', 'page_title', 'page_id' ),
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$this->getConditions( $table ),
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__METHOD__,
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array(
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'STRAIGHT_JOIN',
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'ORDER BY' => $fromField,
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) );
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$this->fullResultCache[$table] = $res;
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}
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$ta = TitleArray::newFromResult( $this->fullResultCache[$table] );
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wfProfileOut( __METHOD__ );
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return $ta;
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}
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/**
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* Get the field name prefix for a given table
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* @param $table String
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* @return null|string
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*/
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protected function getPrefix( $table ) {
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static $prefixes = array(
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'pagelinks' => 'pl',
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'imagelinks' => 'il',
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'categorylinks' => 'cl',
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'templatelinks' => 'tl',
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'redirect' => 'rd',
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);
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if ( isset( $prefixes[$table] ) ) {
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return $prefixes[$table];
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} else {
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$prefix = null;
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wfRunHooks( 'BacklinkCacheGetPrefix', array( $table, &$prefix ) );
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if( $prefix ) {
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return $prefix;
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} else {
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throw new MWException( "Invalid table \"$table\" in " . __CLASS__ );
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}
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}
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}
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/**
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* Get the SQL condition array for selecting backlinks, with a join
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* on the page table.
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* @param $table String
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* @return array|null
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*/
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protected function getConditions( $table ) {
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$prefix = $this->getPrefix( $table );
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// @todo FIXME: imagelinks and categorylinks do not rely on getNamespace,
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// they could be moved up for nicer case statements
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switch ( $table ) {
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case 'pagelinks':
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case 'templatelinks':
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$conds = array(
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"{$prefix}_namespace" => $this->title->getNamespace(),
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"{$prefix}_title" => $this->title->getDBkey(),
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"page_id={$prefix}_from"
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);
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break;
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case 'redirect':
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$conds = array(
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"{$prefix}_namespace" => $this->title->getNamespace(),
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"{$prefix}_title" => $this->title->getDBkey(),
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$this->getDb()->makeList( array(
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"{$prefix}_interwiki = ''",
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"{$prefix}_interwiki is null",
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), LIST_OR ),
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"page_id={$prefix}_from"
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);
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break;
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case 'imagelinks':
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$conds = array(
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'il_to' => $this->title->getDBkey(),
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'page_id=il_from'
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);
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break;
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case 'categorylinks':
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$conds = array(
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'cl_to' => $this->title->getDBkey(),
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'page_id=cl_from',
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);
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break;
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default:
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$conds = null;
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wfRunHooks( 'BacklinkCacheGetConditions', array( $table, $this->title, &$conds ) );
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if( !$conds ) {
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throw new MWException( "Invalid table \"$table\" in " . __CLASS__ );
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}
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}
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return $conds;
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}
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/**
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* Get the approximate number of backlinks
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* @param $table String
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* @return integer
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*/
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public function getNumLinks( $table ) {
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if ( isset( $this->fullResultCache[$table] ) ) {
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return $this->fullResultCache[$table]->numRows();
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}
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if ( isset( $this->partitionCache[$table] ) ) {
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$entry = reset( $this->partitionCache[$table] );
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return $entry['numRows'];
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}
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$titleArray = $this->getLinks( $table );
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return $titleArray->count();
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}
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/**
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* Partition the backlinks into batches.
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* Returns an array giving the start and end of each range. The first
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* batch has a start of false, and the last batch has an end of false.
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*
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* @param $table String: the links table name
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* @param $batchSize Integer
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* @return Array
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*/
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public function partition( $table, $batchSize ) {
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// 1) try partition cache ...
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if ( isset( $this->partitionCache[$table][$batchSize] ) ) {
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wfDebug( __METHOD__ . ": got from partition cache\n" );
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return $this->partitionCache[$table][$batchSize]['batches'];
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}
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$this->partitionCache[$table][$batchSize] = false;
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$cacheEntry =& $this->partitionCache[$table][$batchSize];
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// 2) ... then try full result cache ...
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if ( isset( $this->fullResultCache[$table] ) ) {
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$cacheEntry = $this->partitionResult( $this->fullResultCache[$table], $batchSize );
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wfDebug( __METHOD__ . ": got from full result cache\n" );
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return $cacheEntry['batches'];
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}
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// 3) ... fallback to memcached ...
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global $wgMemc;
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$memcKey = wfMemcKey(
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'backlinks',
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md5( $this->title->getPrefixedDBkey() ),
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$table,
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$batchSize
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);
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$memcValue = $wgMemc->get( $memcKey );
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if ( is_array( $memcValue ) ) {
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$cacheEntry = $memcValue;
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wfDebug( __METHOD__ . ": got from memcached $memcKey\n" );
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return $cacheEntry['batches'];
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}
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// 4) ... finally fetch from the slow database :(
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$this->getLinks( $table );
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$cacheEntry = $this->partitionResult( $this->fullResultCache[$table], $batchSize );
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// Save to memcached
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$wgMemc->set( $memcKey, $cacheEntry, self::CACHE_EXPIRY );
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wfDebug( __METHOD__ . ": got from database\n" );
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return $cacheEntry['batches'];
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}
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/**
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* Partition a DB result with backlinks in it into batches
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* @param $res ResultWrapper database result
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* @param $batchSize integer
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* @return array @see
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*/
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protected function partitionResult( $res, $batchSize ) {
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$batches = array();
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$numRows = $res->numRows();
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$numBatches = ceil( $numRows / $batchSize );
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for ( $i = 0; $i < $numBatches; $i++ ) {
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if ( $i == 0 ) {
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$start = false;
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} else {
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$rowNum = intval( $numRows * $i / $numBatches );
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$res->seek( $rowNum );
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$row = $res->fetchObject();
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$start = $row->page_id;
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}
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if ( $i == $numBatches - 1 ) {
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$end = false;
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} else {
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$rowNum = intval( $numRows * ( $i + 1 ) / $numBatches );
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$res->seek( $rowNum );
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$row = $res->fetchObject();
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$end = $row->page_id - 1;
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}
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# Sanity check order
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if ( $start && $end && $start > $end ) {
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throw new MWException( __METHOD__ . ': Internal error: query result out of order' );
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}
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$batches[] = array( $start, $end );
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}
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return array( 'numRows' => $numRows, 'batches' => $batches );
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}
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}
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