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                 global $wgExternalServers, $wgExternalLoadBalancers;
  36                 if ( !array_key_exists( $cluster, $wgExternalLoadBalancers ) ) {
  37                         $wgExternalLoadBalancers[$cluster] = LoadBalancer::newFromParams( $wgExternalServers[$cluster] );
  38                 }
  39                 $wgExternalLoadBalancers[$cluster]->allowLagged(true);
  40                 return $wgExternalLoadBalancers[$cluster];
  41         }
  42
  43         /** @todo Document.*/
  44         function &getSlave( $cluster ) {
  45                 $lb =& $this->getLoadBalancer( $cluster );
  46                 return $lb->getConnection( DB_SLAVE );
  47         }
  48
  49         /** @todo Document.*/
  50         function &getMaster( $cluster ) {
  51                 $lb =& $this->getLoadBalancer( $cluster );
  52                 return $lb->getConnection( DB_MASTER );
  53         }
  54
  55         /** @todo Document.*/
  56         function getTable( &$db ) {
  57                 $table = $db->getLBInfo( 'blobs table' );
  58                 if ( is_null( $table ) ) {
  59                         $table = 'blobs';
  60                 }
  61                 return $table;
  62         }
  63
  64         /**
  65          * Fetch data from given URL
  66          * @param string $url An url of the form DB://cluster/id or DB://cluster/id/itemid for concatened storage.
  67          */
  68         function fetchFromURL($url) {
  69                 $path = explode( '/', $url );
  70                 $cluster  = $path[2];
  71                 $id       = $path[3];
  72                 if ( isset( $path[4] ) ) {
  73                         $itemID = $path[4];
  74                 } else {
  75                         $itemID = false;
  76                 }
  77
  78                 $ret =& $this->fetchBlob( $cluster, $id, $itemID );
  79
  80                 if ( $itemID !== false && $ret !== false ) {
  81                         return $ret->getItem( $itemID );
  82                 }
  83                 return $ret;
  84         }
  85
  86         /**
  87          * Fetch a blob item out of the database; a cache of the last-loaded
  88          * blob will be kept so that multiple loads out of a multi-item blob
  89          * can avoid redundant database access and decompression.
  90          * @param $cluster
  91          * @param $id
  92          * @param $itemID
  93          * @return mixed
  94          * @private
  95          */
  96         function &fetchBlob( $cluster, $id, $itemID ) {
  97                 global $wgExternalBlobCache;
  98                 $cacheID = ( $itemID === false ) ? "$cluster/$id" : "$cluster/$id/";
  99                 if( isset( $wgExternalBlobCache[$cacheID] ) ) {
 100                         wfDebug( "ExternalStoreDB::fetchBlob cache hit on $cacheID\n" );
 101                         return $wgExternalBlobCache[$cacheID];
 102                 }
 103
 104                 wfDebug( "ExternalStoreDB::fetchBlob cache miss on $cacheID\n" );
 105
 106                 $dbr =& $this->getSlave( $cluster );
 107                 $ret = $dbr->selectField( $this->getTable( $dbr ), 'blob_text', array( 'blob_id' => $id ) );
 108                 if ( $ret === false ) {
 109                         wfDebugLog( 'ExternalStoreDB', "ExternalStoreDB::fetchBlob master fallback on $cacheID\n" );
 110                         // Try the master
 111                         $dbw =& $this->getMaster( $cluster );
 112                         $ret = $dbw->selectField( $this->getTable( $dbw ), 'blob_text', array( 'blob_id' => $id ) );
 113                         if( $ret === false) {
 114                                 wfDebugLog( 'ExternalStoreDB', "ExternalStoreDB::fetchBlob master failed to find $cacheID\n" );
 115                         }
 116                 }
 117                 if( $itemID !== false && $ret !== false ) {
 118                         // Unserialise object; caller extracts item
 119                         $ret = unserialize( $ret );
 120                 }
 121
 122                 $wgExternalBlobCache = array( $cacheID => &$ret );
 123                 return $ret;
 124         }
 125
 126         /**
 127          * Insert a data item into a given cluster
 128          *
 129          * @param $cluster String: the cluster name
 130          * @param $data String: the data item
 131          * @return string URL
 132          */
 133         function store( $cluster, $data ) {
 134                 $fname = 'ExternalStoreDB::store';
 135
 136                 $dbw =& $this->getMaster( $cluster );
 137
 138                 $id = $dbw->nextSequenceValue( 'blob_blob_id_seq' );
 139                 $dbw->insert( $this->getTable( $dbw ), array( 'blob_id' => $id, 'blob_text' => $data ), $fname );
 140                 $id = $dbw->insertId();
 141                 if ( $dbw->getFlag( DBO_TRX ) ) {
 142                         $dbw->immediateCommit();
 143                 }
 144                 return "DB://$cluster/$id";
 145         }
 146 }
 147 ?>