includes/ExternalStoreDB.php

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