ExternalStoreDB.php

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<?php
class ExternalStoreDB {

        function __construct( $params = array() ) {
                $this->mParams = $params;
        }

        function &getLoadBalancer( $cluster ) {
                $wiki = isset($this->mParams['wiki']) ? $this->mParams['wiki'] : false;

                return wfGetLBFactory()->getExternalLB( $cluster, $wiki );
        }

        function &getSlave( $cluster ) {
                global $wgDefaultExternalStore;

                $wiki = isset($this->mParams['wiki']) ? $this->mParams['wiki'] : false;
                $lb =& $this->getLoadBalancer( $cluster );

                if ( !in_array( "DB://" . $cluster, (array)$wgDefaultExternalStore ) ) {
                        wfDebug( "read only external store" );
                        $lb->allowLagged(true);
                } else {
                        wfDebug( "writable external store" );
                }

                return $lb->getConnection( DB_SLAVE, array(), $wiki );
        }

        function &getMaster( $cluster ) {
                $wiki = isset($this->mParams['wiki']) ? $this->mParams['wiki'] : false;
                $lb =& $this->getLoadBalancer( $cluster );
                return $lb->getConnection( DB_MASTER, array(), $wiki );
        }

        function getTable( &$db ) {
                $table = $db->getLBInfo( 'blobs table' );
                if ( is_null( $table ) ) {
                        $table = 'blobs';
                }
                return $table;
        }

        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;
        }

        function &fetchBlob( $cluster, $id, $itemID ) {
                static $externalBlobCache = array();

                $cacheID = ( $itemID === false ) ? "$cluster/$id" : "$cluster/$id/";
                if( isset( $externalBlobCache[$cacheID] ) ) {
                        wfDebug( "ExternalStoreDB::fetchBlob cache hit on $cacheID\n" );
                        return $externalBlobCache[$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 ), __METHOD__ );
                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 ), __METHOD__ );
                        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 );
                }

                $externalBlobCache = array( $cacheID => &$ret );
                return $ret;
        }

        function store( $cluster, $data ) {
                $dbw = $this->getMaster( $cluster );
                $id = $dbw->nextSequenceValue( 'blob_blob_id_seq' );
                $dbw->insert( $this->getTable( $dbw ),
                        array( 'blob_id' => $id, 'blob_text' => $data ),
                        __METHOD__ );
                $id = $dbw->insertId();
                if ( !$id ) {
                        throw new MWException( __METHOD__.': no insert ID' );
                }
                if ( $dbw->getFlag( DBO_TRX ) ) {
                        $dbw->commit( __METHOD__ );
                }
                return "DB://$cluster/$id";
        }
}