Made BackLinkCache use object caching better.
authorAaron Schulz <aschulz@wikimedia.org>
Tue, 27 Nov 2012 17:26:02 +0000 (09:26 -0800)
committerAaron Schulz <aschulz@wikimedia.org>
Tue, 27 Nov 2012 17:41:50 +0000 (09:41 -0800)
* This way, we can actually get persistent cache hits for
the HTMLCacheUpdate queries rather than always hitting a DB.
* Also moved BacklinkCache under the /cache directory.

Change-Id: I0666ee575fb42675f1a7dd9cb52665f0a12a66a9

includes/AutoLoader.php
includes/BacklinkCache.php [deleted file]
includes/cache/BacklinkCache.php [new file with mode: 0644]

index 9bdf377..31c1571 100644 (file)
@@ -38,7 +38,6 @@ $wgAutoloadLocalClasses = array(
        'AuthPlugin' => 'includes/AuthPlugin.php',
        'AuthPluginUser' => 'includes/AuthPlugin.php',
        'Autopromote' => 'includes/Autopromote.php',
-       'BacklinkCache' => 'includes/BacklinkCache.php',
        'BadTitleError' => 'includes/Exception.php',
        'BaseTemplate' => 'includes/SkinTemplate.php',
        'Block' => 'includes/Block.php',
@@ -425,6 +424,7 @@ $wgAutoloadLocalClasses = array(
        'UsageException' => 'includes/api/ApiMain.php',
 
        # includes/cache
+       'BacklinkCache' => 'includes/cache/BacklinkCache.php',
        'CacheDependency' => 'includes/cache/CacheDependency.php',
        'ConstantDependency' => 'includes/cache/CacheDependency.php',
        'DependencyWrapper' => 'includes/cache/CacheDependency.php',
diff --git a/includes/BacklinkCache.php b/includes/BacklinkCache.php
deleted file mode 100644 (file)
index ba8691b..0000000
+++ /dev/null
@@ -1,423 +0,0 @@
-<?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
- */
-
-/**
- * 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
- *
- * @internal documentation reviewed on 18 Mar 2011 by hashar
- */
-class BacklinkCache {
-       /** @var ProcessCacheLRU */
-       protected static $cache;
-
-       /**
-        * Multi dimensions array representing batches. Keys are:
-        *  > (string) links table name
-        *    > 'numRows' : Number of rows for this link table
-        *    > 'batches' : array( $start, $end )
-        *
-        * @see BacklinkCache::partitionResult()
-        *
-        * Cleared with BacklinkCache::clear()
-        */
-       protected $partitionCache = array();
-
-       /**
-        * 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()
-        */
-       protected $fullResultCache = array();
-
-       /**
-        * 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;
-       }
-
-       /**
-        * 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 $title ) {
-               if ( !self::$cache ) { // init cache
-                       self::$cache = new ProcessCacheLRU( 1 );
-               }
-               $dbKey = $title->getPrefixedDBkey();
-               if ( !self::$cache->has( $dbKey, 'obj' ) ) {
-                       self::$cache->set( $dbKey, 'obj', new self( $title ) );
-               }
-               return self::$cache->get( $dbKey, 'obj' );
-       }
-
-       /**
-        * 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 array( 'partitionCache', 'fullResultCache', 'title' );
-       }
-
-       /**
-        * Clear locally stored data and database object.
-        */
-       public function clear() {
-               $this->partitionCache = array();
-               $this->fullResultCache = array();
-               unset( $this->db );
-       }
-
-       /**
-        * Set the Database object to use
-        *
-        * @param $db DatabaseBase
-        */
-       public function setDB( $db ) {
-               $this->db = $db;
-       }
-
-       /**
-        * Get the slave connection to the database
-        * When non existing, will initialize the connection.
-        * @return DatabaseBase object
-        */
-       protected function getDB() {
-               if ( !isset( $this->db ) ) {
-                       $this->db = wfGetDB( DB_SLAVE );
-               }
-
-               return $this->db;
-       }
-
-       /**
-        * Get the backlinks for a given table. Cached in process memory only.
-        * @param $table String
-        * @param $startId Integer or false
-        * @param $endId Integer or false
-        * @return TitleArrayFromResult
-        */
-       public function getLinks( $table, $startId = false, $endId = false ) {
-               wfProfileIn( __METHOD__ );
-
-               $fromField = $this->getPrefix( $table ) . '_from';
-
-               if ( $startId || $endId ) {
-                       // Partial range, not cached
-                       wfDebug( __METHOD__ . ": from DB (uncacheable range)\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 );
-                       }
-
-                       $res = $this->getDB()->select(
-                               array( $table, 'page' ),
-                               array( 'page_namespace', 'page_title', 'page_id' ),
-                               $conds,
-                               __METHOD__,
-                               array(
-                                       'STRAIGHT_JOIN',
-                                       'ORDER BY' => $fromField
-                               ) );
-                       $ta = TitleArray::newFromResult( $res );
-
-                       wfProfileOut( __METHOD__ );
-                       return $ta;
-               }
-
-               // @todo FIXME: Make this a function?
-               if ( !isset( $this->fullResultCache[$table] ) ) {
-                       wfDebug( __METHOD__ . ": from DB\n" );
-                       $res = $this->getDB()->select(
-                               array( $table, 'page' ),
-                               array( 'page_namespace', 'page_title', 'page_id' ),
-                               $this->getConditions( $table ),
-                               __METHOD__,
-                               array(
-                                       'STRAIGHT_JOIN',
-                                       'ORDER BY' => $fromField,
-                               ) );
-                       $this->fullResultCache[$table] = $res;
-               }
-
-               $ta = TitleArray::newFromResult( $this->fullResultCache[$table] );
-
-               wfProfileOut( __METHOD__ );
-               return $ta;
-       }
-
-       /**
-        * Get the field name prefix for a given table
-        * @param $table String
-        * @throws MWException
-        * @return null|string
-        */
-       protected function getPrefix( $table ) {
-               static $prefixes = array(
-                       'pagelinks'     => 'pl',
-                       'imagelinks'    => 'il',
-                       'categorylinks' => 'cl',
-                       'templatelinks' => 'tl',
-                       'redirect'      => 'rd',
-               );
-
-               if ( isset( $prefixes[$table] ) ) {
-                       return $prefixes[$table];
-               } else {
-                       $prefix = null;
-                       wfRunHooks( 'BacklinkCacheGetPrefix', array( $table, &$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 $table String
-        * @throws MWException
-        * @return array|null
-        */
-       protected function getConditions( $table ) {
-               $prefix = $this->getPrefix( $table );
-
-               // @todo FIXME: imagelinks and categorylinks do not rely on getNamespace,
-               // they could be moved up for nicer case statements
-               switch ( $table ) {
-                       case 'pagelinks':
-                       case 'templatelinks':
-                               $conds = array(
-                                       "{$prefix}_namespace" => $this->title->getNamespace(),
-                                       "{$prefix}_title"     => $this->title->getDBkey(),
-                                       "page_id={$prefix}_from"
-                               );
-                               break;
-                       case 'redirect':
-                               $conds = array(
-                                       "{$prefix}_namespace" => $this->title->getNamespace(),
-                                       "{$prefix}_title"     => $this->title->getDBkey(),
-                                       $this->getDb()->makeList( array(
-                                               "{$prefix}_interwiki = ''",
-                                               "{$prefix}_interwiki is null",
-                                       ), LIST_OR ),
-                                       "page_id={$prefix}_from"
-                               );
-                               break;
-                       case 'imagelinks':
-                               $conds = array(
-                                       'il_to' => $this->title->getDBkey(),
-                                       'page_id=il_from'
-                               );
-                               break;
-                       case 'categorylinks':
-                               $conds = array(
-                                       'cl_to' => $this->title->getDBkey(),
-                                       'page_id=cl_from',
-                               );
-                               break;
-                       default:
-                               $conds = null;
-                               wfRunHooks( 'BacklinkCacheGetConditions', array( $table, $this->title, &$conds ) );
-                               if( !$conds ) {
-                                       throw new MWException( "Invalid table \"$table\" in " . __CLASS__ );
-                               }
-               }
-
-               return $conds;
-       }
-
-       /**
-        * Get the approximate number of backlinks
-        * @param $table String
-        * @return integer
-        */
-       public function getNumLinks( $table ) {
-               if ( isset( $this->fullResultCache[$table] ) ) {
-                       return $this->fullResultCache[$table]->numRows();
-               }
-
-               if ( isset( $this->partitionCache[$table] ) ) {
-                       $entry = reset( $this->partitionCache[$table] );
-                       return $entry['numRows'];
-               }
-
-               $titleArray = $this->getLinks( $table );
-
-               return $titleArray->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 $table String: the links table name
-        * @param $batchSize Integer
-        * @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'];
-               }
-
-               // 3) ... fallback to memcached ...
-
-               global $wgMemc;
-
-               $memcKey = wfMemcKey(
-                       'backlinks',
-                       md5( $this->title->getPrefixedDBkey() ),
-                       $table,
-                       $batchSize
-               );
-
-               $memcValue = $wgMemc->get( $memcKey );
-
-               if ( is_array( $memcValue ) ) {
-                       $cacheEntry = $memcValue;
-                       wfDebug( __METHOD__ . ": got from memcached $memcKey\n" );
-
-                       return $cacheEntry['batches'];
-               }
-
-
-               // 4) ... finally fetch from the slow database :(
-
-               $this->getLinks( $table );
-               $cacheEntry = $this->partitionResult( $this->fullResultCache[$table], $batchSize );
-               // Save to memcached
-               $wgMemc->set( $memcKey, $cacheEntry, self::CACHE_EXPIRY );
-
-               wfDebug( __METHOD__ . ": got from database\n" );
-               return $cacheEntry['batches'];
-       }
-
-       /**
-        * Partition a DB result with backlinks in it into batches
-        * @param $res ResultWrapper database result
-        * @param $batchSize integer
-        * @throws MWException
-        * @return array @see
-        */
-       protected function partitionResult( $res, $batchSize ) {
-               $batches = array();
-               $numRows = $res->numRows();
-               $numBatches = ceil( $numRows / $batchSize );
-
-               for ( $i = 0; $i < $numBatches; $i++ ) {
-                       if ( $i == 0  ) {
-                               $start = false;
-                       } else {
-                               $rowNum = intval( $numRows * $i / $numBatches );
-                               $res->seek( $rowNum );
-                               $row = $res->fetchObject();
-                               $start = $row->page_id;
-                       }
-
-                       if ( $i == $numBatches - 1 ) {
-                               $end = false;
-                       } else {
-                               $rowNum = intval( $numRows * ( $i + 1 ) / $numBatches );
-                               $res->seek( $rowNum );
-                               $row = $res->fetchObject();
-                               $end = $row->page_id - 1;
-                       }
-
-                       # Sanity check order
-                       if ( $start && $end && $start > $end ) {
-                               throw new MWException( __METHOD__ . ': Internal error: query result out of order' );
-                       }
-
-                       $batches[] = array( $start, $end );
-               }
-
-               return array( 'numRows' => $numRows, 'batches' => $batches );
-       }
-}
diff --git a/includes/cache/BacklinkCache.php b/includes/cache/BacklinkCache.php
new file mode 100644 (file)
index 0000000..c4f8762
--- /dev/null
@@ -0,0 +1,433 @@
+<?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
+ */
+
+/**
+ * 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
+ *
+ * @internal documentation reviewed on 18 Mar 2011 by hashar
+ */
+class BacklinkCache {
+       /** @var ProcessCacheLRU */
+       protected static $cache;
+
+       /**
+        * Multi dimensions array representing batches. Keys are:
+        *  > (string) links table name
+        *    > 'numRows' : Number of rows for this link table
+        *    > 'batches' : array( $start, $end )
+        *
+        * @see BacklinkCache::partitionResult()
+        *
+        * Cleared with BacklinkCache::clear()
+        */
+       protected $partitionCache = array();
+
+       /**
+        * 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()
+        */
+       protected $fullResultCache = array();
+
+       /**
+        * 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;
+       }
+
+       /**
+        * 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 $title ) {
+               if ( !self::$cache ) { // init cache
+                       self::$cache = new ProcessCacheLRU( 1 );
+               }
+               $dbKey = $title->getPrefixedDBkey();
+               if ( !self::$cache->has( $dbKey, 'obj' ) ) {
+                       self::$cache->set( $dbKey, 'obj', new self( $title ) );
+               }
+               return self::$cache->get( $dbKey, 'obj' );
+       }
+
+       /**
+        * 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 array( 'partitionCache', 'fullResultCache', 'title' );
+       }
+
+       /**
+        * Clear locally stored data and database object.
+        */
+       public function clear() {
+               $this->partitionCache = array();
+               $this->fullResultCache = array();
+               unset( $this->db );
+       }
+
+       /**
+        * Set the Database object to use
+        *
+        * @param $db DatabaseBase
+        */
+       public function setDB( $db ) {
+               $this->db = $db;
+       }
+
+       /**
+        * Get the slave connection to the database
+        * When non existing, will initialize the connection.
+        * @return DatabaseBase object
+        */
+       protected function getDB() {
+               if ( !isset( $this->db ) ) {
+                       $this->db = wfGetDB( DB_SLAVE );
+               }
+
+               return $this->db;
+       }
+
+       /**
+        * Get the backlinks for a given table. Cached in process memory only.
+        * @param $table String
+        * @param $startId Integer or false
+        * @param $endId Integer or false
+        * @return TitleArrayFromResult
+        */
+       public function getLinks( $table, $startId = false, $endId = false ) {
+               wfProfileIn( __METHOD__ );
+
+               $fromField = $this->getPrefix( $table ) . '_from';
+
+               if ( $startId || $endId ) {
+                       // Partial range, not cached
+                       wfDebug( __METHOD__ . ": from DB (uncacheable range)\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 );
+                       }
+
+                       $res = $this->getDB()->select(
+                               array( $table, 'page' ),
+                               array( 'page_namespace', 'page_title', 'page_id' ),
+                               $conds,
+                               __METHOD__,
+                               array(
+                                       'STRAIGHT_JOIN',
+                                       'ORDER BY' => $fromField
+                               ) );
+                       $ta = TitleArray::newFromResult( $res );
+
+                       wfProfileOut( __METHOD__ );
+                       return $ta;
+               }
+
+               // @todo FIXME: Make this a function?
+               if ( !isset( $this->fullResultCache[$table] ) ) {
+                       wfDebug( __METHOD__ . ": from DB\n" );
+                       $res = $this->getDB()->select(
+                               array( $table, 'page' ),
+                               array( 'page_namespace', 'page_title', 'page_id' ),
+                               $this->getConditions( $table ),
+                               __METHOD__,
+                               array(
+                                       'STRAIGHT_JOIN',
+                                       'ORDER BY' => $fromField,
+                               ) );
+                       $this->fullResultCache[$table] = $res;
+               }
+
+               $ta = TitleArray::newFromResult( $this->fullResultCache[$table] );
+
+               wfProfileOut( __METHOD__ );
+               return $ta;
+       }
+
+       /**
+        * Get the field name prefix for a given table
+        * @param $table String
+        * @throws MWException
+        * @return null|string
+        */
+       protected function getPrefix( $table ) {
+               static $prefixes = array(
+                       'pagelinks'     => 'pl',
+                       'imagelinks'    => 'il',
+                       'categorylinks' => 'cl',
+                       'templatelinks' => 'tl',
+                       'redirect'      => 'rd',
+               );
+
+               if ( isset( $prefixes[$table] ) ) {
+                       return $prefixes[$table];
+               } else {
+                       $prefix = null;
+                       wfRunHooks( 'BacklinkCacheGetPrefix', array( $table, &$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 $table String
+        * @throws MWException
+        * @return array|null
+        */
+       protected function getConditions( $table ) {
+               $prefix = $this->getPrefix( $table );
+
+               // @todo FIXME: imagelinks and categorylinks do not rely on getNamespace,
+               // they could be moved up for nicer case statements
+               switch ( $table ) {
+                       case 'pagelinks':
+                       case 'templatelinks':
+                               $conds = array(
+                                       "{$prefix}_namespace" => $this->title->getNamespace(),
+                                       "{$prefix}_title"     => $this->title->getDBkey(),
+                                       "page_id={$prefix}_from"
+                               );
+                               break;
+                       case 'redirect':
+                               $conds = array(
+                                       "{$prefix}_namespace" => $this->title->getNamespace(),
+                                       "{$prefix}_title"     => $this->title->getDBkey(),
+                                       $this->getDb()->makeList( array(
+                                               "{$prefix}_interwiki = ''",
+                                               "{$prefix}_interwiki is null",
+                                       ), LIST_OR ),
+                                       "page_id={$prefix}_from"
+                               );
+                               break;
+                       case 'imagelinks':
+                               $conds = array(
+                                       'il_to' => $this->title->getDBkey(),
+                                       'page_id=il_from'
+                               );
+                               break;
+                       case 'categorylinks':
+                               $conds = array(
+                                       'cl_to' => $this->title->getDBkey(),
+                                       'page_id=cl_from',
+                               );
+                               break;
+                       default:
+                               $conds = null;
+                               wfRunHooks( 'BacklinkCacheGetConditions', array( $table, $this->title, &$conds ) );
+                               if( !$conds ) {
+                                       throw new MWException( "Invalid table \"$table\" in " . __CLASS__ );
+                               }
+               }
+
+               return $conds;
+       }
+
+       /**
+        * Get the approximate number of backlinks
+        * @param $table String
+        * @return integer
+        */
+       public function getNumLinks( $table ) {
+               global $wgMemc;
+
+               // 1) try partition cache ...
+               if ( isset( $this->partitionCache[$table] ) ) {
+                       $entry = reset( $this->partitionCache[$table] );
+                       return $entry['numRows'];
+               }
+
+               // 2) ... then try full result cache ...
+               if ( isset( $this->fullResultCache[$table] ) ) {
+                       return $this->fullResultCache[$table]->numRows();
+               }
+
+               $memcKey = wfMemcKey( 'numbacklinks', md5( $this->title->getPrefixedDBkey() ), $table );
+
+               // 3) ... fallback to memcached ...
+               $count = $wgMemc->get( $memcKey );
+               if ( $count ) {
+                       return $count;
+               }
+
+               // 4) fetch from the database ...
+               $count = $this->getLinks( $table )->count();
+               $wgMemc->set( $memcKey, $count, self::CACHE_EXPIRY );
+
+               return $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 $table String: the links table name
+        * @param $batchSize Integer
+        * @return Array
+        */
+       public function partition( $table, $batchSize ) {
+               global $wgMemc;
+
+               // 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 = wfMemcKey(
+                       'backlinks',
+                       md5( $this->title->getPrefixedDBkey() ),
+                       $table,
+                       $batchSize
+               );
+
+               // 3) ... fallback to memcached ...
+               $memcValue = $wgMemc->get( $memcKey );
+               if ( is_array( $memcValue ) ) {
+                       $cacheEntry = $memcValue;
+                       wfDebug( __METHOD__ . ": got from memcached $memcKey\n" );
+                       return $cacheEntry['batches'];
+               }
+
+
+               // 4) ... finally fetch from the slow database :(
+               $this->getLinks( $table );
+               $cacheEntry = $this->partitionResult( $this->fullResultCache[$table], $batchSize );
+               // Save partitions to memcached
+               $wgMemc->set( $memcKey, $cacheEntry, self::CACHE_EXPIRY );
+
+               // Save backlink count to memcached
+               $memcKey = wfMemcKey( 'numbacklinks', md5( $this->title->getPrefixedDBkey() ), $table );
+               $wgMemc->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 $res ResultWrapper database result
+        * @param $batchSize integer
+        * @throws MWException
+        * @return array @see
+        */
+       protected function partitionResult( $res, $batchSize ) {
+               $batches = array();
+               $numRows = $res->numRows();
+               $numBatches = ceil( $numRows / $batchSize );
+
+               for ( $i = 0; $i < $numBatches; $i++ ) {
+                       if ( $i == 0  ) {
+                               $start = false;
+                       } else {
+                               $rowNum = intval( $numRows * $i / $numBatches );
+                               $res->seek( $rowNum );
+                               $row = $res->fetchObject();
+                               $start = $row->page_id;
+                       }
+
+                       if ( $i == $numBatches - 1 ) {
+                               $end = false;
+                       } else {
+                               $rowNum = intval( $numRows * ( $i + 1 ) / $numBatches );
+                               $res->seek( $rowNum );
+                               $row = $res->fetchObject();
+                               $end = $row->page_id - 1;
+                       }
+
+                       # Sanity check order
+                       if ( $start && $end && $start > $end ) {
+                               throw new MWException( __METHOD__ . ': Internal error: query result out of order' );
+                       }
+
+                       $batches[] = array( $start, $end );
+               }
+
+               return array( 'numRows' => $numRows, 'batches' => $batches );
+       }
+}