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