includes/ExternalStoreDB.php

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