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         /** @todo Document.*/
  34         function &getLoadBalancer( $cluster ) {
  35                 $wiki = isset($this->mParams['wiki']) ? $this->mParams['wiki'] : false;
  36
  37                 return wfGetLBFactory()->getExternalLB( $cluster, $wiki );
  38         }
  39
  40         /** @todo Document.*/
  41         function &getSlave( $cluster ) {
  42                 $wiki = isset($this->mParams['wiki']) ? $this->mParams['wiki'] : false;
  43                 $lb =& $this->getLoadBalancer( $cluster );
  44                 return $lb->getConnection( DB_SLAVE, array(), $wiki );
  45         }
  46
  47         /** @todo Document.*/
  48         function &getMaster( $cluster ) {
  49                 $wiki = isset($this->mParams['wiki']) ? $this->mParams['wiki'] : false;
  50                 $lb =& $this->getLoadBalancer( $cluster );
  51                 return $lb->getConnection( DB_MASTER, array(), $wiki );
  52         }
  53
  54         /** @todo Document.*/
  55         function getTable( &$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 string $url 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                 global $wgExternalBlobCache;
  97                 $cacheID = ( $itemID === false ) ? "$cluster/$id" : "$cluster/$id/";
  98                 if( isset( $wgExternalBlobCache[$cacheID] ) ) {
  99                         wfDebug( "ExternalStoreDB::fetchBlob cache hit on $cacheID\n" );
 100                         return $wgExternalBlobCache[$cacheID];
 101                 }
 102
 103                 wfDebug( "ExternalStoreDB::fetchBlob cache miss on $cacheID\n" );
 104
 105                 $dbr =& $this->getSlave( $cluster );
 106                 $ret = $dbr->selectField( $this->getTable( $dbr ), 'blob_text', array( 'blob_id' => $id ) );
 107                 if ( $ret === false ) {
 108                         wfDebugLog( 'ExternalStoreDB', "ExternalStoreDB::fetchBlob master fallback on $cacheID\n" );
 109                         // Try the master
 110                         $dbw =& $this->getMaster( $cluster );
 111                         $ret = $dbw->selectField( $this->getTable( $dbw ), 'blob_text', array( 'blob_id' => $id ) );
 112                         if( $ret === false) {
 113                                 wfDebugLog( 'ExternalStoreDB', "ExternalStoreDB::fetchBlob master failed to find $cacheID\n" );
 114                         }
 115                 }
 116                 if( $itemID !== false && $ret !== false ) {
 117                         // Unserialise object; caller extracts item
 118                         $ret = unserialize( $ret );
 119                 }
 120
 121                 $wgExternalBlobCache = array( $cacheID => &$ret );
 122                 return $ret;
 123         }
 124
 125         /**
 126          * Insert a data item into a given cluster
 127          *
 128          * @param $cluster String: the cluster name
 129          * @param $data String: the data item
 130          * @return string URL
 131          */
 132         function store( $cluster, $data ) {
 133                 $dbw = $this->getMaster( $cluster );
 134                 $id = $dbw->nextSequenceValue( 'blob_blob_id_seq' );
 135                 $dbw->insert( $this->getTable( $dbw ),
 136                         array( 'blob_id' => $id, 'blob_text' => $data ),
 137                         __METHOD__ );
 138                 $id = $dbw->insertId();
 139                 if ( !$id ) {
 140                         throw new MWException( __METHOD__.': no insert ID' );
 141                 }
 142                 if ( $dbw->getFlag( DBO_TRX ) ) {
 143                         $dbw->commit();
 144                 }
 145                 return "DB://$cluster/$id";
 146         }
 147 }