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         function __construct( $params = array() ) {
  30                 $this->mParams = $params;
  31         }
  32
  33         /**
  34          * Get a LoadBalancer for the specified cluster
  35          *
  36          * @param $cluster String: cluster name
  37          * @return LoadBalancer object
  38          */
  39         function &getLoadBalancer( $cluster ) {
  40                 $wiki = isset($this->mParams['wiki']) ? $this->mParams['wiki'] : false;
  41
  42                 return wfGetLBFactory()->getExternalLB( $cluster, $wiki );
  43         }
  44
  45         /**
  46          * Get a slave database connection for the specified cluster
  47          *
  48          * @param $cluster String: cluster name
  49          * @return DatabaseBase object
  50          */
  51         function &getSlave( $cluster ) {
  52                 $wiki = isset($this->mParams['wiki']) ? $this->mParams['wiki'] : false;
  53                 $lb =& $this->getLoadBalancer( $cluster );
  54                 return $lb->getConnection( DB_SLAVE, array(), $wiki );
  55         }
  56
  57         /**
  58          * Get a master database connection for the specified cluster
  59          *
  60          * @param $cluster String: cluster name
  61          * @return DatabaseBase object
  62          */
  63         function &getMaster( $cluster ) {
  64                 $wiki = isset($this->mParams['wiki']) ? $this->mParams['wiki'] : false;
  65                 $lb =& $this->getLoadBalancer( $cluster );
  66                 return $lb->getConnection( DB_MASTER, array(), $wiki );
  67         }
  68
  69         /**
  70          * Get the 'blobs' table name for this database
  71          *
  72          * @param $db DatabaseBase
  73          * @return String: table name ('blobs' by default)
  74          */
  75         function getTable( &$db ) {
  76                 $table = $db->getLBInfo( 'blobs table' );
  77                 if ( is_null( $table ) ) {
  78                         $table = 'blobs';
  79                 }
  80                 return $table;
  81         }
  82
  83         /**
  84          * Fetch data from given URL
  85          * @param $url String: an url of the form DB://cluster/id or DB://cluster/id/itemid for concatened storage.
  86          */
  87         function fetchFromURL( $url ) {
  88                 $path = explode( '/', $url );
  89                 $cluster  = $path[2];
  90                 $id       = $path[3];
  91                 if ( isset( $path[4] ) ) {
  92                         $itemID = $path[4];
  93                 } else {
  94                         $itemID = false;
  95                 }
  96
  97                 $ret =& $this->fetchBlob( $cluster, $id, $itemID );
  98
  99                 if ( $itemID !== false && $ret !== false ) {
 100                         return $ret->getItem( $itemID );
 101                 }
 102                 return $ret;
 103         }
 104
 105         /**
 106          * Fetch a blob item out of the database; a cache of the last-loaded
 107          * blob will be kept so that multiple loads out of a multi-item blob
 108          * can avoid redundant database access and decompression.
 109          * @param $cluster
 110          * @param $id
 111          * @param $itemID
 112          * @return mixed
 113          * @private
 114          */
 115         function &fetchBlob( $cluster, $id, $itemID ) {
 116                 global $wgExternalBlobCache;
 117                 $cacheID = ( $itemID === false ) ? "$cluster/$id" : "$cluster/$id/";
 118                 if( isset( $wgExternalBlobCache[$cacheID] ) ) {
 119                         wfDebug( "ExternalStoreDB::fetchBlob cache hit on $cacheID\n" );
 120                         return $wgExternalBlobCache[$cacheID];
 121                 }
 122
 123                 wfDebug( "ExternalStoreDB::fetchBlob cache miss on $cacheID\n" );
 124
 125                 $dbr =& $this->getSlave( $cluster );
 126                 $ret = $dbr->selectField( $this->getTable( $dbr ), 'blob_text', array( 'blob_id' => $id ) );
 127                 if ( $ret === false ) {
 128                         wfDebugLog( 'ExternalStoreDB', "ExternalStoreDB::fetchBlob master fallback on $cacheID\n" );
 129                         // Try the master
 130                         $dbw =& $this->getMaster( $cluster );
 131                         $ret = $dbw->selectField( $this->getTable( $dbw ), 'blob_text', array( 'blob_id' => $id ) );
 132                         if( $ret === false) {
 133                                 wfDebugLog( 'ExternalStoreDB', "ExternalStoreDB::fetchBlob master failed to find $cacheID\n" );
 134                         }
 135                 }
 136                 if( $itemID !== false && $ret !== false ) {
 137                         // Unserialise object; caller extracts item
 138                         $ret = unserialize( $ret );
 139                 }
 140
 141                 $wgExternalBlobCache = array( $cacheID => &$ret );
 142                 return $ret;
 143         }
 144
 145         /**
 146          * Insert a data item into a given cluster
 147          *
 148          * @param $cluster String: the cluster name
 149          * @param $data String: the data item
 150          * @return string URL
 151          */
 152         function store( $cluster, $data ) {
 153                 $dbw = $this->getMaster( $cluster );
 154                 $id = $dbw->nextSequenceValue( 'blob_blob_id_seq' );
 155                 $dbw->insert( $this->getTable( $dbw ),
 156                         array( 'blob_id' => $id, 'blob_text' => $data ),
 157                         __METHOD__ );
 158                 $id = $dbw->insertId();
 159                 if ( !$id ) {
 160                         throw new MWException( __METHOD__.': no insert ID' );
 161                 }
 162                 if ( $dbw->getFlag( DBO_TRX ) ) {
 163                         $dbw->commit();
 164                 }
 165                 return "DB://$cluster/$id";
 166         }
 167 }