includes/externalstore/ExternalStoreDB.php

   1 <?php
   2 /**
   3  * External storage in SQL database.
   4  *
   5  * This program is free software; you can redistribute it and/or modify
   6  * it under the terms of the GNU General Public License as published by
   7  * the Free Software Foundation; either version 2 of the License, or
   8  * (at your option) any later version.
   9  *
  10  * This program is distributed in the hope that it will be useful,
  11  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  12  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
  13  * GNU General Public License for more details.
  14  *
  15  * You should have received a copy of the GNU General Public License along
  16  * with this program; if not, write to the Free Software Foundation, Inc.,
  17  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
  18  * http://www.gnu.org/copyleft/gpl.html
  19  *
  20  * @file
  21  */
  22
  23 /**
  24  * DB accessable external objects.
  25  *
  26  * In this system, each store "location" maps to a database "cluster".
  27  * The clusters must be defined in the normal LBFactory configuration.
  28  *
  29  * @ingroup ExternalStorage
  30  */
  31 class ExternalStoreDB extends ExternalStoreMedium {
  32         /**
  33          * The URL returned is of the form of the form DB://cluster/id
  34          * or DB://cluster/id/itemid for concatened storage.
  35          *
  36          * @see ExternalStoreMedium::fetchFromURL()
  37          */
  38         public function fetchFromURL( $url ) {
  39                 $path = explode( '/', $url );
  40                 $cluster = $path[2];
  41                 $id = $path[3];
  42                 if ( isset( $path[4] ) ) {
  43                         $itemID = $path[4];
  44                 } else {
  45                         $itemID = false;
  46                 }
  47
  48                 $ret =& $this->fetchBlob( $cluster, $id, $itemID );
  49
  50                 if ( $itemID !== false && $ret !== false ) {
  51                         return $ret->getItem( $itemID );
  52                 }
  53                 return $ret;
  54         }
  55
  56         /**
  57          * @see ExternalStoreMedium::store()
  58          */
  59         public function store( $cluster, $data ) {
  60                 $dbw = $this->getMaster( $cluster );
  61                 $id = $dbw->nextSequenceValue( 'blob_blob_id_seq' );
  62                 $dbw->insert( $this->getTable( $dbw ),
  63                         array( 'blob_id' => $id, 'blob_text' => $data ),
  64                         __METHOD__ );
  65                 $id = $dbw->insertId();
  66                 if ( !$id ) {
  67                         throw new MWException( __METHOD__ . ': no insert ID' );
  68                 }
  69                 if ( $dbw->getFlag( DBO_TRX ) ) {
  70                         $dbw->commit( __METHOD__ );
  71                 }
  72                 return "DB://$cluster/$id";
  73         }
  74
  75         /**
  76          * Get a LoadBalancer for the specified cluster
  77          *
  78          * @param string $cluster cluster name
  79          * @return LoadBalancer object
  80          */
  81         function &getLoadBalancer( $cluster ) {
  82                 $wiki = isset( $this->params['wiki'] ) ? $this->params['wiki'] : false;
  83
  84                 return wfGetLBFactory()->getExternalLB( $cluster, $wiki );
  85         }
  86
  87         /**
  88          * Get a slave database connection for the specified cluster
  89          *
  90          * @param string $cluster cluster name
  91          * @return DatabaseBase object
  92          */
  93         function &getSlave( $cluster ) {
  94                 global $wgDefaultExternalStore;
  95
  96                 $wiki = isset( $this->params['wiki'] ) ? $this->params['wiki'] : false;
  97                 $lb =& $this->getLoadBalancer( $cluster );
  98
  99                 if ( !in_array( "DB://" . $cluster, (array)$wgDefaultExternalStore ) ) {
 100                         wfDebug( "read only external store" );
 101                         $lb->allowLagged( true );
 102                 } else {
 103                         wfDebug( "writable external store" );
 104                 }
 105
 106                 return $lb->getConnection( DB_SLAVE, array(), $wiki );
 107         }
 108
 109         /**
 110          * Get a master database connection for the specified cluster
 111          *
 112          * @param string $cluster cluster name
 113          * @return DatabaseBase object
 114          */
 115         function &getMaster( $cluster ) {
 116                 $wiki = isset( $this->params['wiki'] ) ? $this->params['wiki'] : false;
 117                 $lb =& $this->getLoadBalancer( $cluster );
 118                 return $lb->getConnection( DB_MASTER, array(), $wiki );
 119         }
 120
 121         /**
 122          * Get the 'blobs' table name for this database
 123          *
 124          * @param $db DatabaseBase
 125          * @return String: table name ('blobs' by default)
 126          */
 127         function getTable( &$db ) {
 128                 $table = $db->getLBInfo( 'blobs table' );
 129                 if ( is_null( $table ) ) {
 130                         $table = 'blobs';
 131                 }
 132                 return $table;
 133         }
 134
 135         /**
 136          * Fetch a blob item out of the database; a cache of the last-loaded
 137          * blob will be kept so that multiple loads out of a multi-item blob
 138          * can avoid redundant database access and decompression.
 139          * @param $cluster
 140          * @param $id
 141          * @param $itemID
 142          * @return mixed
 143          * @private
 144          */
 145         function &fetchBlob( $cluster, $id, $itemID ) {
 146                 /**
 147                  * One-step cache variable to hold base blobs; operations that
 148                  * pull multiple revisions may often pull multiple times from
 149                  * the same blob. By keeping the last-used one open, we avoid
 150                  * redundant unserialization and decompression overhead.
 151                  */
 152                 static $externalBlobCache = array();
 153
 154                 $cacheID = ( $itemID === false ) ? "$cluster/$id" : "$cluster/$id/";
 155                 if ( isset( $externalBlobCache[$cacheID] ) ) {
 156                         wfDebugLog( 'ExternalStoreDB-cache', "ExternalStoreDB::fetchBlob cache hit on $cacheID\n" );
 157                         return $externalBlobCache[$cacheID];
 158                 }
 159
 160                 wfDebugLog( 'ExternalStoreDB-cache', "ExternalStoreDB::fetchBlob cache miss on $cacheID\n" );
 161
 162                 $dbr =& $this->getSlave( $cluster );
 163                 $ret = $dbr->selectField( $this->getTable( $dbr ), 'blob_text', array( 'blob_id' => $id ), __METHOD__ );
 164                 if ( $ret === false ) {
 165                         wfDebugLog( 'ExternalStoreDB', "ExternalStoreDB::fetchBlob master fallback on $cacheID\n" );
 166                         // Try the master
 167                         $dbw =& $this->getMaster( $cluster );
 168                         $ret = $dbw->selectField( $this->getTable( $dbw ), 'blob_text', array( 'blob_id' => $id ), __METHOD__ );
 169                         if ( $ret === false ) {
 170                                 wfDebugLog( 'ExternalStoreDB', "ExternalStoreDB::fetchBlob master failed to find $cacheID\n" );
 171                         }
 172                 }
 173                 if ( $itemID !== false && $ret !== false ) {
 174                         // Unserialise object; caller extracts item
 175                         $ret = unserialize( $ret );
 176                 }
 177
 178                 $externalBlobCache = array( $cacheID => &$ret );
 179                 return $ret;
 180         }
 181 }