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          * Fetch data from given URL
  37          * @param string $url An url
  38          */
  39
  40         function &getLoadBalancer( $cluster ) {
  41                 global $wgExternalServers, $wgExternalLoadBalancers;
  42                 if ( !array_key_exists( $cluster, $wgExternalLoadBalancers ) ) {
  43                         $wgExternalLoadBalancers[$cluster] = LoadBalancer::newFromParams( $wgExternalServers[$cluster] );
  44                 }
  45                 $wgExternalLoadBalancers[$cluster]->allowLagged(true);
  46                 return $wgExternalLoadBalancers[$cluster];
  47         }
  48
  49         function &getSlave( $cluster ) {
  50                 $lb =& $this->getLoadBalancer( $cluster );
  51                 return $lb->getConnection( DB_SLAVE );
  52         }
  53
  54         function &getMaster( $cluster ) {
  55                 $lb =& $this->getLoadBalancer( $cluster );
  56                 return $lb->getConnection( DB_MASTER );
  57         }
  58
  59         function getTable( &$db ) {
  60                 $table = $db->getLBInfo( 'blobs table' );
  61                 if ( is_null( $table ) ) {
  62                         $table = 'blobs';
  63                 }
  64                 return $table;
  65         }
  66
  67         function fetchFromURL($url) {
  68                 #
  69                 # URLs have the form DB://cluster/id or DB://cluster/id/itemid for concatenated storage
  70                 #
  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          * @return mixed
  93          * @access private
  94          */
  95         function &fetchBlob( $cluster, $id, $itemID ) {
  96                 global $wgExternalBlobCache;
  97                 $cacheID = ( $itemID === false ) ? "$cluster/$id" : "$cluster/$id/";
  98                 if( isset( $wgExternalBlobCache[$cacheID] ) ) {
  99                         wfDebug( "ExternalStoreDB::fetchBlob cache hit on $cacheID\n" );
 100                         return $wgExternalBlobCache[$cacheID];
 101                 }
 102
 103                 wfDebug( "ExternalStoreDB::fetchBlob cache miss on $cacheID\n" );
 104
 105                 $dbr =& $this->getSlave( $cluster );
 106                 $ret = $dbr->selectField( $this->getTable( $dbr ), 'blob_text', array( 'blob_id' => $id ) );
 107                 if ( $ret === false ) {
 108                         wfDebugLog( 'ExternalStoreDB', "ExternalStoreDB::fetchBlob master fallback on $cacheID\n" );
 109                         // Try the master
 110                         $dbw =& $this->getMaster( $cluster );
 111                         $ret = $dbw->selectField( $this->getTable( $dbw ), 'blob_text', array( 'blob_id' => $id ) );
 112                         if( $ret === false) {
 113                                 wfDebugLog( 'ExternalStoreDB', "ExternalStoreDB::fetchBlob master failed to find $cacheID\n" );
 114                         }
 115                 }
 116                 if( $itemID !== false && $ret !== false ) {
 117                         // Unserialise object; caller extracts item
 118                         $ret = unserialize( $ret );
 119                 }
 120
 121                 $wgExternalBlobCache = array( $cacheID => &$ret );
 122                 return $ret;
 123         }
 124
 125         /**
 126          * Insert a data item into a given cluster
 127          *
 128          * @param string $cluster The cluster name
 129          * @param string $data The data item
 130          * @return string URL
 131          */
 132         function store( $cluster, $data ) {
 133                 $fname = 'ExternalStoreDB::store';
 134
 135                 $dbw =& $this->getMaster( $cluster );
 136
 137                 $id = $dbw->nextSequenceValue( 'blob_blob_id_seq' );
 138                 $dbw->insert( $this->getTable( $dbw ), array( 'blob_id' => $id, 'blob_text' => $data ), $fname );
 139                 $id = $dbw->insertId();
 140                 if ( $dbw->getFlag( DBO_TRX ) ) {
 141                         $dbw->immediateCommit();
 142                 }
 143                 return "DB://$cluster/$id";
 144         }
 145 }
 146 ?>