includes/ExternalStoreDB.php

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