includes/ExternalStoreDB.php

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