includes/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  * @ingroup ExternalStorage
  26  */
  27 class ExternalStoreDB {
  28
  29         /**
  30          * @param $params array
  31          */
  32         function __construct( $params = array() ) {
  33                 $this->mParams = $params;
  34         }
  35
  36         /**
  37          * Get a LoadBalancer for the specified cluster
  38          *
  39          * @param $cluster String: cluster name
  40          * @return LoadBalancer object
  41          */
  42         function &getLoadBalancer( $cluster ) {
  43                 $wiki = isset($this->mParams['wiki']) ? $this->mParams['wiki'] : false;
  44
  45                 return wfGetLBFactory()->getExternalLB( $cluster, $wiki );
  46         }
  47
  48         /**
  49          * Get a slave database connection for the specified cluster
  50          *
  51          * @param $cluster String: cluster name
  52          * @return DatabaseBase object
  53          */
  54         function &getSlave( $cluster ) {
  55                 global $wgDefaultExternalStore;
  56
  57                 $wiki = isset($this->mParams['wiki']) ? $this->mParams['wiki'] : false;
  58                 $lb =& $this->getLoadBalancer( $cluster );
  59
  60                 if ( !in_array( "DB://" . $cluster, (array)$wgDefaultExternalStore ) ) {
  61                         wfDebug( "read only external store" );
  62                         $lb->allowLagged(true);
  63                 } else {
  64                         wfDebug( "writable external store" );
  65                 }
  66
  67                 return $lb->getConnection( DB_SLAVE, array(), $wiki );
  68         }
  69
  70         /**
  71          * Get a master database connection for the specified cluster
  72          *
  73          * @param $cluster String: cluster name
  74          * @return DatabaseBase object
  75          */
  76         function &getMaster( $cluster ) {
  77                 $wiki = isset($this->mParams['wiki']) ? $this->mParams['wiki'] : false;
  78                 $lb =& $this->getLoadBalancer( $cluster );
  79                 return $lb->getConnection( DB_MASTER, array(), $wiki );
  80         }
  81
  82         /**
  83          * Get the 'blobs' table name for this database
  84          *
  85          * @param $db DatabaseBase
  86          * @return String: table name ('blobs' by default)
  87          */
  88         function getTable( &$db ) {
  89                 $table = $db->getLBInfo( 'blobs table' );
  90                 if ( is_null( $table ) ) {
  91                         $table = 'blobs';
  92                 }
  93                 return $table;
  94         }
  95
  96         /**
  97          * Fetch data from given URL
  98          * @param $url String: an url of the form DB://cluster/id or DB://cluster/id/itemid for concatened storage.
  99          * @return mixed
 100          */
 101         function fetchFromURL( $url ) {
 102                 $path = explode( '/', $url );
 103                 $cluster = $path[2];
 104                 $id = $path[3];
 105                 if ( isset( $path[4] ) ) {
 106                         $itemID = $path[4];
 107                 } else {
 108                         $itemID = false;
 109                 }
 110
 111                 $ret =& $this->fetchBlob( $cluster, $id, $itemID );
 112
 113                 if ( $itemID !== false && $ret !== false ) {
 114                         return $ret->getItem( $itemID );
 115                 }
 116                 return $ret;
 117         }
 118
 119         /**
 120          * Fetch a blob item out of the database; a cache of the last-loaded
 121          * blob will be kept so that multiple loads out of a multi-item blob
 122          * can avoid redundant database access and decompression.
 123          * @param $cluster
 124          * @param $id
 125          * @param $itemID
 126          * @return mixed
 127          * @private
 128          */
 129         function &fetchBlob( $cluster, $id, $itemID ) {
 130                 /**
 131                  * One-step cache variable to hold base blobs; operations that
 132                  * pull multiple revisions may often pull multiple times from
 133                  * the same blob. By keeping the last-used one open, we avoid
 134                  * redundant unserialization and decompression overhead.
 135                  */
 136                 static $externalBlobCache = array();
 137
 138                 $cacheID = ( $itemID === false ) ? "$cluster/$id" : "$cluster/$id/";
 139                 if( isset( $externalBlobCache[$cacheID] ) ) {
 140                         wfDebug( "ExternalStoreDB::fetchBlob cache hit on $cacheID\n" );
 141                         return $externalBlobCache[$cacheID];
 142                 }
 143
 144                 wfDebug( "ExternalStoreDB::fetchBlob cache miss on $cacheID\n" );
 145
 146                 $dbr =& $this->getSlave( $cluster );
 147                 $ret = $dbr->selectField( $this->getTable( $dbr ), 'blob_text', array( 'blob_id' => $id ), __METHOD__ );
 148                 if ( $ret === false ) {
 149                         wfDebugLog( 'ExternalStoreDB', "ExternalStoreDB::fetchBlob master fallback on $cacheID\n" );
 150                         // Try the master
 151                         $dbw =& $this->getMaster( $cluster );
 152                         $ret = $dbw->selectField( $this->getTable( $dbw ), 'blob_text', array( 'blob_id' => $id ), __METHOD__ );
 153                         if( $ret === false) {
 154                                 wfDebugLog( 'ExternalStoreDB', "ExternalStoreDB::fetchBlob master failed to find $cacheID\n" );
 155                         }
 156                 }
 157                 if( $itemID !== false && $ret !== false ) {
 158                         // Unserialise object; caller extracts item
 159                         $ret = unserialize( $ret );
 160                 }
 161
 162                 $externalBlobCache = array( $cacheID => &$ret );
 163                 return $ret;
 164         }
 165
 166         /**
 167          * Insert a data item into a given cluster
 168          *
 169          * @param $cluster String: the cluster name
 170          * @param $data String: the data item
 171          * @throws MWException
 172          * @return string URL
 173          */
 174         function store( $cluster, $data ) {
 175                 $dbw = $this->getMaster( $cluster );
 176                 $id = $dbw->nextSequenceValue( 'blob_blob_id_seq' );
 177                 $dbw->insert( $this->getTable( $dbw ),
 178                         array( 'blob_id' => $id, 'blob_text' => $data ),
 179                         __METHOD__ );
 180                 $id = $dbw->insertId();
 181                 if ( !$id ) {
 182                         throw new MWException( __METHOD__.': no insert ID' );
 183                 }
 184                 if ( $dbw->getFlag( DBO_TRX ) ) {
 185                         $dbw->commit( __METHOD__ );
 186                 }
 187                 return "DB://$cluster/$id";
 188         }
 189 }