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