includes/ExternalStoreDB.php

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