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<?php
/**
* DB accessable external objects
* @ingroup ExternalStorage
*/
class ExternalStoreDB {
function __construct( $params = array() ) {
$this->mParams = $params;
}
/**
* Get a LoadBalancer for the specified cluster
*
* @param $cluster String: cluster name
* @return LoadBalancer object
*/
function &getLoadBalancer( $cluster ) {
$wiki = isset($this->mParams['wiki']) ? $this->mParams['wiki'] : false;
return wfGetLBFactory()->getExternalLB( $cluster, $wiki );
}
/**
* Get a slave database connection for the specified cluster
*
* @param $cluster String: cluster name
* @return DatabaseBase object
*/
function &getSlave( $cluster ) {
global $wgDefaultExternalStore;
$wiki = isset($this->mParams['wiki']) ? $this->mParams['wiki'] : false;
$lb =& $this->getLoadBalancer( $cluster );
if ( !in_array( "DB://" . $cluster, (array)$wgDefaultExternalStore ) ) {
wfDebug( "read only external store" );
$lb->allowLagged(true);
} else {
wfDebug( "writable external store" );
}
return $lb->getConnection( DB_SLAVE, array(), $wiki );
}
/**
* Get a master database connection for the specified cluster
*
* @param $cluster String: cluster name
* @return DatabaseBase object
*/
function &getMaster( $cluster ) {
$wiki = isset($this->mParams['wiki']) ? $this->mParams['wiki'] : false;
$lb =& $this->getLoadBalancer( $cluster );
return $lb->getConnection( DB_MASTER, array(), $wiki );
}
/**
* Get the 'blobs' table name for this database
*
* @param $db DatabaseBase
* @return String: table name ('blobs' by default)
*/
function getTable( &$db ) {
$table = $db->getLBInfo( 'blobs table' );
if ( is_null( $table ) ) {
$table = 'blobs';
}
return $table;
}
/**
* Fetch data from given URL
* @param $url String: an url of the form DB://cluster/id or DB://cluster/id/itemid for concatened storage.
*/
function fetchFromURL( $url ) {
$path = explode( '/', $url );
$cluster = $path[2];
$id = $path[3];
if ( isset( $path[4] ) ) {
$itemID = $path[4];
} else {
$itemID = false;
}
$ret =& $this->fetchBlob( $cluster, $id, $itemID );
if ( $itemID !== false && $ret !== false ) {
return $ret->getItem( $itemID );
}
return $ret;
}
/**
* Fetch a blob item out of the database; a cache of the last-loaded
* blob will be kept so that multiple loads out of a multi-item blob
* can avoid redundant database access and decompression.
* @param $cluster
* @param $id
* @param $itemID
* @return mixed
* @private
*/
function &fetchBlob( $cluster, $id, $itemID ) {
/**
* One-step cache variable to hold base blobs; operations that
* pull multiple revisions may often pull multiple times from
* the same blob. By keeping the last-used one open, we avoid
* redundant unserialization and decompression overhead.
*/
static $externalBlobCache = array();
$cacheID = ( $itemID === false ) ? "$cluster/$id" : "$cluster/$id/";
if( isset( $externalBlobCache[$cacheID] ) ) {
wfDebug( "ExternalStoreDB::fetchBlob cache hit on $cacheID\n" );
return $externalBlobCache[$cacheID];
}
wfDebug( "ExternalStoreDB::fetchBlob cache miss on $cacheID\n" );
$dbr =& $this->getSlave( $cluster );
$ret = $dbr->selectField( $this->getTable( $dbr ), 'blob_text', array( 'blob_id' => $id ), __METHOD__ );
if ( $ret === false ) {
wfDebugLog( 'ExternalStoreDB', "ExternalStoreDB::fetchBlob master fallback on $cacheID\n" );
// Try the master
$dbw =& $this->getMaster( $cluster );
$ret = $dbw->selectField( $this->getTable( $dbw ), 'blob_text', array( 'blob_id' => $id ), __METHOD__ );
if( $ret === false) {
wfDebugLog( 'ExternalStoreDB', "ExternalStoreDB::fetchBlob master failed to find $cacheID\n" );
}
}
if( $itemID !== false && $ret !== false ) {
// Unserialise object; caller extracts item
$ret = unserialize( $ret );
}
$externalBlobCache = array( $cacheID => &$ret );
return $ret;
}
/**
* Insert a data item into a given cluster
*
* @param $cluster String: the cluster name
* @param $data String: the data item
* @return string URL
*/
function store( $cluster, $data ) {
$dbw = $this->getMaster( $cluster );
$id = $dbw->nextSequenceValue( 'blob_blob_id_seq' );
$dbw->insert( $this->getTable( $dbw ),
array( 'blob_id' => $id, 'blob_text' => $data ),
__METHOD__ );
$id = $dbw->insertId();
if ( !$id ) {
throw new MWException( __METHOD__.': no insert ID' );
}
if ( $dbw->getFlag( DBO_TRX ) ) {
$dbw->commit();
}
return "DB://$cluster/$id";
}
}
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