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Diffstat (limited to 'includes/BacklinkCache.php')
| -rw-r--r-- | includes/BacklinkCache.php | 232 |
1 files changed, 232 insertions, 0 deletions
diff --git a/includes/BacklinkCache.php b/includes/BacklinkCache.php new file mode 100644 index 00000000..a7bcd858 --- /dev/null +++ b/includes/BacklinkCache.php @@ -0,0 +1,232 @@ +<?php + +/** + * Class for fetching backlink lists, approximate backlink counts and partitions. + * Instances of this class should typically be fetched with $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. + */ +class BacklinkCache { + var $partitionCache = array(); + var $fullResultCache = array(); + var $title; + var $db; + + const CACHE_EXPIRY = 3600; + + /** + * Create a new BacklinkCache + */ + function __construct( $title ) { + $this->title = $title; + } + + /** + * Clear locally stored data + */ + function clear() { + $this->partitionCache = array(); + $this->fullResultCache = array(); + unset( $this->db ); + } + + /** + * Set the Database object to use + */ + public function setDB( $db ) { + $this->db = $db; + } + + 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 string $table + * @return TitleArray + */ + public function getLinks( $table, $startId = false, $endId = false ) { + wfProfileIn( __METHOD__ ); + + 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. + $fromField = $this->getPrefix( $table ) . '_from'; + 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') ); + $ta = TitleArray::newFromResult( $res ); + wfProfileOut( __METHOD__ ); + return $ta; + } + + 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') ); + $this->fullResultCache[$table] = $res; + } + $ta = TitleArray::newFromResult( $this->fullResultCache[$table] ); + wfProfileOut( __METHOD__ ); + return $ta; + } + + /** + * Get the field name prefix for a given table + */ + 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 { + throw new MWException( "Invalid table \"$table\" in " . __CLASS__ ); + } + } + + /** + * Get the SQL condition array for selecting backlinks, with a join on the page table + */ + protected function getConditions( $table ) { + $prefix = $this->getPrefix( $table ); + switch ( $table ) { + case 'pagelinks': + case 'templatelinks': + case 'redirect': + $conds = array( + "{$prefix}_namespace" => $this->title->getNamespace(), + "{$prefix}_title" => $this->title->getDBkey(), + "page_id={$prefix}_from" + ); + break; + case 'imagelinks': + $conds = array( + 'il_to' => $this->title->getDBkey(), + 'page_id=il_from' + ); + break; + case 'categorylinks': + $conds = array( + 'cl_to' => $this->title->getDBkey(), + 'page_id=cl_from', + ); + break; + default: + throw new MWException( "Invalid table \"$table\" in " . __CLASS__ ); + } + return $conds; + } + + /** + * Get the approximate number of backlinks + */ + 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 string $table The links table name + * @param integer $batchSize + * @return array + */ + public function partition( $table, $batchSize ) { + // Try 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]; + + // 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']; + } + // Try 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']; + } + // Fetch from 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 + */ + 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; + } + $batches[] = array( $start, $end ); + } + return array( 'numRows' => $numRows, 'batches' => $batches ); + } +} |