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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
+ */
+
+/**
+ * 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;
+ }
+
+ /**
+ * Check if there are any backlinks
+ * @param $table String
+ * @return bool
+ */
+ public function hasLinks( $table ) {
+ return ( $this->getNumLinks( $table, 1 ) > 0 );
+ }
+
+ /**
+ * Get the approximate number of backlinks
+ * @param $table String
+ * @param $max integer Only count up to this many backlinks
+ * @return integer
+ */
+ public function getNumLinks( $table, $max = INF ) {
+ global $wgMemc;
+
+ // 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 = wfMemcKey( 'numbacklinks', md5( $this->title->getPrefixedDBkey() ), $table );
+
+ // 3) ... fallback to memcached ...
+ $count = $wgMemc->get( $memcKey );
+ if ( $count ) {
+ return min( $max, $count );
+ }
+
+ // 4) fetch from the database ...
+ if ( is_infinite( $max ) ) { // full count
+ $count = $this->getLinks( $table )->count();
+ $wgMemc->set( $memcKey, $count, self::CACHE_EXPIRY );
+ } else { // with limit
+ $count = $this->getDB()->select(
+ array( $table, 'page' ),
+ '1',
+ $this->getConditions( $table ),
+ __METHOD__,
+ array( 'LIMIT' => $max )
+ )->numRows();
+ }
+
+ 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 string $table 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 );
+ }
+}
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