includes/ExternalStoreDB.php

   1 <?php
   2 /**
   3  *
   4  * @package MediaWiki
   5  *
   6  * DB accessable external objects
   7  *
   8  */
   9 require_once( 'LoadBalancer.php' );
  10
  11
  12 /** @package MediaWiki */
  13
  14 /**
  15  * External database storage will use one (or more) separate connection pools
  16  * from what the main wiki uses. If we load many revisions, such as when doing
  17  * bulk backups or maintenance, we want to keep them around over the lifetime
  18  * of the script.
  19  *
  20  * Associative array of LoadBalancer objects, indexed by cluster name.
  21  */
  22 global $wgExternalLoadBalancers;
  23 $wgExternalLoadBalancers = array();
  24
  25 /**
  26  * One-step cache variable to hold base blobs; operations that
  27  * pull multiple revisions may often pull multiple times from
  28  * the same blob. By keeping the last-used one open, we avoid
  29  * redundant unserialization and decompression overhead.
  30  */
  31 global $wgExternalBlobCache;
  32 $wgExternalBlobCache = array();
  33
  34 class ExternalStoreDB {
  35
  36         /** @todo Document.*/
  37         function &getLoadBalancer( $cluster ) {
  38                 global $wgExternalServers, $wgExternalLoadBalancers;
  39                 if ( !array_key_exists( $cluster, $wgExternalLoadBalancers ) ) {
  40                         $wgExternalLoadBalancers[$cluster] = LoadBalancer::newFromParams( $wgExternalServers[$cluster] );
  41                 }
  42                 $wgExternalLoadBalancers[$cluster]->allowLagged(true);
  43                 return $wgExternalLoadBalancers[$cluster];
  44         }
  45
  46         /** @todo Document.*/
  47         function &getSlave( $cluster ) {
  48                 $lb =& $this->getLoadBalancer( $cluster );
  49                 return $lb->getConnection( DB_SLAVE );
  50         }
  51
  52         /** @todo Document.*/
  53         function &getMaster( $cluster ) {
  54                 $lb =& $this->getLoadBalancer( $cluster );
  55                 return $lb->getConnection( DB_MASTER );
  56         }
  57
  58         /** @todo Document.*/
  59         function getTable( &$db ) {
  60                 $table = $db->getLBInfo( 'blobs table' );
  61                 if ( is_null( $table ) ) {
  62                         $table = 'blobs';
  63                 }
  64                 return $table;
  65         }
  66
  67         /**
  68          * Fetch data from given URL
  69          * @param string $url An url of the form DB://cluster/id or DB://cluster/id/itemid for concatened storage.
  70          */
  71         function fetchFromURL($url) {
  72                 $path = explode( '/', $url );
  73                 $cluster  = $path[2];
  74                 $id       = $path[3];
  75                 if ( isset( $path[4] ) ) {
  76                         $itemID = $path[4];
  77                 } else {
  78                         $itemID = false;
  79                 }
  80
  81                 $ret =& $this->fetchBlob( $cluster, $id, $itemID );
  82
  83                 if ( $itemID !== false && $ret !== false ) {
  84                         return $ret->getItem( $itemID );
  85                 }
  86                 return $ret;
  87         }
  88
  89         /**
  90          * Fetch a blob item out of the database; a cache of the last-loaded
  91          * blob will be kept so that multiple loads out of a multi-item blob
  92          * can avoid redundant database access and decompression.
  93          * @param $cluster
  94          * @param $id
  95          * @param $itemID
  96          * @return mixed
  97          * @private
  98          */
  99         function &fetchBlob( $cluster, $id, $itemID ) {
 100                 global $wgExternalBlobCache;
 101                 $cacheID = ( $itemID === false ) ? "$cluster/$id" : "$cluster/$id/";
 102                 if( isset( $wgExternalBlobCache[$cacheID] ) ) {
 103                         wfDebug( "ExternalStoreDB::fetchBlob cache hit on $cacheID\n" );
 104                         return $wgExternalBlobCache[$cacheID];
 105                 }
 106
 107                 wfDebug( "ExternalStoreDB::fetchBlob cache miss on $cacheID\n" );
 108
 109                 $dbr =& $this->getSlave( $cluster );
 110                 $ret = $dbr->selectField( $this->getTable( $dbr ), 'blob_text', array( 'blob_id' => $id ) );
 111                 if ( $ret === false ) {
 112                         wfDebugLog( 'ExternalStoreDB', "ExternalStoreDB::fetchBlob master fallback on $cacheID\n" );
 113                         // Try the master
 114                         $dbw =& $this->getMaster( $cluster );
 115                         $ret = $dbw->selectField( $this->getTable( $dbw ), 'blob_text', array( 'blob_id' => $id ) );
 116                         if( $ret === false) {
 117                                 wfDebugLog( 'ExternalStoreDB', "ExternalStoreDB::fetchBlob master failed to find $cacheID\n" );
 118                         }
 119                 }
 120                 if( $itemID !== false && $ret !== false ) {
 121                         // Unserialise object; caller extracts item
 122                         $ret = unserialize( $ret );
 123                 }
 124
 125                 $wgExternalBlobCache = array( $cacheID => &$ret );
 126                 return $ret;
 127         }
 128
 129         /**
 130          * Insert a data item into a given cluster
 131          *
 132          * @param $cluster String: the cluster name
 133          * @param $data String: the data item
 134          * @return string URL
 135          */
 136         function store( $cluster, $data ) {
 137                 $fname = 'ExternalStoreDB::store';
 138
 139                 $dbw =& $this->getMaster( $cluster );
 140
 141                 $id = $dbw->nextSequenceValue( 'blob_blob_id_seq' );
 142                 $dbw->insert( $this->getTable( $dbw ), array( 'blob_id' => $id, 'blob_text' => $data ), $fname );
 143                 $id = $dbw->insertId();
 144                 if ( $dbw->getFlag( DBO_TRX ) ) {
 145                         $dbw->immediateCommit();
 146                 }
 147                 return "DB://$cluster/$id";
 148         }
 149 }
 150 ?>