includes/ExternalStoreDB.php

   1 <?php
   2
   3 /**
   4  * DB accessable external objects
   5  * @ingroup ExternalStorage
   6  */
   7 class ExternalStoreDB {
   8
   9         function __construct( $params = array() ) {
  10                 $this->mParams = $params;
  11         }
  12
  13         /**
  14          * Get a LoadBalancer for the specified cluster
  15          *
  16          * @param $cluster String: cluster name
  17          * @return LoadBalancer object
  18          */
  19         function &getLoadBalancer( $cluster ) {
  20                 $wiki = isset($this->mParams['wiki']) ? $this->mParams['wiki'] : false;
  21
  22                 return wfGetLBFactory()->getExternalLB( $cluster, $wiki );
  23         }
  24
  25         /**
  26          * Get a slave database connection for the specified cluster
  27          *
  28          * @param $cluster String: cluster name
  29          * @return DatabaseBase object
  30          */
  31         function &getSlave( $cluster ) {
  32                 global $wgDefaultExternalStore;
  33
  34                 $wiki = isset($this->mParams['wiki']) ? $this->mParams['wiki'] : false;
  35                 $lb =& $this->getLoadBalancer( $cluster );
  36
  37                 if ( !in_array( "DB://" . $cluster, (array)$wgDefaultExternalStore ) ) {
  38                         wfDebug( "read only external store" );
  39                         $lb->allowLagged(true);
  40                 } else {
  41                         wfDebug( "writable external store" );
  42                 }
  43
  44                 return $lb->getConnection( DB_SLAVE, array(), $wiki );
  45         }
  46
  47         /**
  48          * Get a master database connection for the specified cluster
  49          *
  50          * @param $cluster String: cluster name
  51          * @return DatabaseBase object
  52          */
  53         function &getMaster( $cluster ) {
  54                 $wiki = isset($this->mParams['wiki']) ? $this->mParams['wiki'] : false;
  55                 $lb =& $this->getLoadBalancer( $cluster );
  56                 return $lb->getConnection( DB_MASTER, array(), $wiki );
  57         }
  58
  59         /**
  60          * Get the 'blobs' table name for this database
  61          *
  62          * @param $db DatabaseBase
  63          * @return String: table name ('blobs' by default)
  64          */
  65         function getTable( &$db ) {
  66                 $table = $db->getLBInfo( 'blobs table' );
  67                 if ( is_null( $table ) ) {
  68                         $table = 'blobs';
  69                 }
  70                 return $table;
  71         }
  72
  73         /**
  74          * Fetch data from given URL
  75          * @param $url String: an url of the form DB://cluster/id or DB://cluster/id/itemid for concatened storage.
  76          * @return mixed
  77          */
  78         function fetchFromURL( $url ) {
  79                 $path = explode( '/', $url );
  80                 $cluster  = $path[2];
  81                 $id       = $path[3];
  82                 if ( isset( $path[4] ) ) {
  83                         $itemID = $path[4];
  84                 } else {
  85                         $itemID = false;
  86                 }
  87
  88                 $ret =& $this->fetchBlob( $cluster, $id, $itemID );
  89
  90                 if ( $itemID !== false && $ret !== false ) {
  91                         return $ret->getItem( $itemID );
  92                 }
  93                 return $ret;
  94         }
  95
  96         /**
  97          * Fetch a blob item out of the database; a cache of the last-loaded
  98          * blob will be kept so that multiple loads out of a multi-item blob
  99          * can avoid redundant database access and decompression.
 100          * @param $cluster
 101          * @param $id
 102          * @param $itemID
 103          * @return mixed
 104          * @private
 105          */
 106         function &fetchBlob( $cluster, $id, $itemID ) {
 107                 /**
 108                  * One-step cache variable to hold base blobs; operations that
 109                  * pull multiple revisions may often pull multiple times from
 110                  * the same blob. By keeping the last-used one open, we avoid
 111                  * redundant unserialization and decompression overhead.
 112                  */
 113                 static $externalBlobCache = array();
 114
 115                 $cacheID = ( $itemID === false ) ? "$cluster/$id" : "$cluster/$id/";
 116                 if( isset( $externalBlobCache[$cacheID] ) ) {
 117                         wfDebug( "ExternalStoreDB::fetchBlob cache hit on $cacheID\n" );
 118                         return $externalBlobCache[$cacheID];
 119                 }
 120
 121                 wfDebug( "ExternalStoreDB::fetchBlob cache miss on $cacheID\n" );
 122
 123                 $dbr =& $this->getSlave( $cluster );
 124                 $ret = $dbr->selectField( $this->getTable( $dbr ), 'blob_text', array( 'blob_id' => $id ), __METHOD__ );
 125                 if ( $ret === false ) {
 126                         wfDebugLog( 'ExternalStoreDB', "ExternalStoreDB::fetchBlob master fallback on $cacheID\n" );
 127                         // Try the master
 128                         $dbw =& $this->getMaster( $cluster );
 129                         $ret = $dbw->selectField( $this->getTable( $dbw ), 'blob_text', array( 'blob_id' => $id ), __METHOD__ );
 130                         if( $ret === false) {
 131                                 wfDebugLog( 'ExternalStoreDB', "ExternalStoreDB::fetchBlob master failed to find $cacheID\n" );
 132                         }
 133                 }
 134                 if( $itemID !== false && $ret !== false ) {
 135                         // Unserialise object; caller extracts item
 136                         $ret = unserialize( $ret );
 137                 }
 138
 139                 $externalBlobCache = array( $cacheID => &$ret );
 140                 return $ret;
 141         }
 142
 143         /**
 144          * Insert a data item into a given cluster
 145          *
 146          * @param $cluster String: the cluster name
 147          * @param $data String: the data item
 148          * @return string URL
 149          */
 150         function store( $cluster, $data ) {
 151                 $dbw = $this->getMaster( $cluster );
 152                 $id = $dbw->nextSequenceValue( 'blob_blob_id_seq' );
 153                 $dbw->insert( $this->getTable( $dbw ),
 154                         array( 'blob_id' => $id, 'blob_text' => $data ),
 155                         __METHOD__ );
 156                 $id = $dbw->insertId();
 157                 if ( !$id ) {
 158                         throw new MWException( __METHOD__.': no insert ID' );
 159                 }
 160                 if ( $dbw->getFlag( DBO_TRX ) ) {
 161                         $dbw->commit( __METHOD__ );
 162                 }
 163                 return "DB://$cluster/$id";
 164         }
 165 }