diff options
Diffstat (limited to 'includes/ExternalStoreDB.php')
-rw-r--r-- | includes/ExternalStoreDB.php | 150 |
1 files changed, 150 insertions, 0 deletions
diff --git a/includes/ExternalStoreDB.php b/includes/ExternalStoreDB.php new file mode 100644 index 00000000..f610df80 --- /dev/null +++ b/includes/ExternalStoreDB.php @@ -0,0 +1,150 @@ +<?php +/** + * + * @package MediaWiki + * + * DB accessable external objects + * + */ +require_once( 'LoadBalancer.php' ); + + +/** @package MediaWiki */ + +/** + * External database storage will use one (or more) separate connection pools + * from what the main wiki uses. If we load many revisions, such as when doing + * bulk backups or maintenance, we want to keep them around over the lifetime + * of the script. + * + * Associative array of LoadBalancer objects, indexed by cluster name. + */ +global $wgExternalLoadBalancers; +$wgExternalLoadBalancers = array(); + +/** + * One-step cache variable to hold base blobs; operations that + * pull multiple revisions may often pull multiple times from + * the same blob. By keeping the last-used one open, we avoid + * redundant unserialization and decompression overhead. + */ +global $wgExternalBlobCache; +$wgExternalBlobCache = array(); + +class ExternalStoreDB { + + /** @todo Document.*/ + function &getLoadBalancer( $cluster ) { + global $wgExternalServers, $wgExternalLoadBalancers; + if ( !array_key_exists( $cluster, $wgExternalLoadBalancers ) ) { + $wgExternalLoadBalancers[$cluster] = LoadBalancer::newFromParams( $wgExternalServers[$cluster] ); + } + $wgExternalLoadBalancers[$cluster]->allowLagged(true); + return $wgExternalLoadBalancers[$cluster]; + } + + /** @todo Document.*/ + function &getSlave( $cluster ) { + $lb =& $this->getLoadBalancer( $cluster ); + return $lb->getConnection( DB_SLAVE ); + } + + /** @todo Document.*/ + function &getMaster( $cluster ) { + $lb =& $this->getLoadBalancer( $cluster ); + return $lb->getConnection( DB_MASTER ); + } + + /** @todo Document.*/ + function getTable( &$db ) { + $table = $db->getLBInfo( 'blobs table' ); + if ( is_null( $table ) ) { + $table = 'blobs'; + } + return $table; + } + + /** + * Fetch data from given URL + * @param string $url An url of the form DB://cluster/id or DB://cluster/id/itemid for concatened storage. + */ + function fetchFromURL($url) { + $path = explode( '/', $url ); + $cluster = $path[2]; + $id = $path[3]; + if ( isset( $path[4] ) ) { + $itemID = $path[4]; + } else { + $itemID = false; + } + + $ret =& $this->fetchBlob( $cluster, $id, $itemID ); + + if ( $itemID !== false && $ret !== false ) { + return $ret->getItem( $itemID ); + } + return $ret; + } + + /** + * Fetch a blob item out of the database; a cache of the last-loaded + * blob will be kept so that multiple loads out of a multi-item blob + * can avoid redundant database access and decompression. + * @param $cluster + * @param $id + * @param $itemID + * @return mixed + * @private + */ + function &fetchBlob( $cluster, $id, $itemID ) { + global $wgExternalBlobCache; + $cacheID = ( $itemID === false ) ? "$cluster/$id" : "$cluster/$id/"; + if( isset( $wgExternalBlobCache[$cacheID] ) ) { + wfDebug( "ExternalStoreDB::fetchBlob cache hit on $cacheID\n" ); + return $wgExternalBlobCache[$cacheID]; + } + + wfDebug( "ExternalStoreDB::fetchBlob cache miss on $cacheID\n" ); + + $dbr =& $this->getSlave( $cluster ); + $ret = $dbr->selectField( $this->getTable( $dbr ), 'blob_text', array( 'blob_id' => $id ) ); + if ( $ret === false ) { + wfDebugLog( 'ExternalStoreDB', "ExternalStoreDB::fetchBlob master fallback on $cacheID\n" ); + // Try the master + $dbw =& $this->getMaster( $cluster ); + $ret = $dbw->selectField( $this->getTable( $dbw ), 'blob_text', array( 'blob_id' => $id ) ); + if( $ret === false) { + wfDebugLog( 'ExternalStoreDB', "ExternalStoreDB::fetchBlob master failed to find $cacheID\n" ); + } + } + if( $itemID !== false && $ret !== false ) { + // Unserialise object; caller extracts item + $ret = unserialize( $ret ); + } + + $wgExternalBlobCache = array( $cacheID => &$ret ); + return $ret; + } + + /** + * Insert a data item into a given cluster + * + * @param $cluster String: the cluster name + * @param $data String: the data item + * @return string URL + */ + function store( $cluster, $data ) { + $fname = 'ExternalStoreDB::store'; + + $dbw =& $this->getMaster( $cluster ); + + $id = $dbw->nextSequenceValue( 'blob_blob_id_seq' ); + $dbw->insert( $this->getTable( $dbw ), array( 'blob_id' => $id, 'blob_text' => $data ), $fname ); + $id = $dbw->insertId(); + if ( $dbw->getFlag( DBO_TRX ) ) { + $dbw->immediateCommit(); + } + return "DB://$cluster/$id"; + } +} +?> |