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<?php
/**
*
* @package MediaWiki
*
* DB accessable external objects
*
*/
require_once( 'LoadBalancer.php' );
/** @package MediaWiki */
/**
* External database storage will use one (or more) separate connection pools
* from what the main wiki uses. If we load many revisions, such as when doing
* bulk backups or maintenance, we want to keep them around over the lifetime
* of the script.
*
* Associative array of LoadBalancer objects, indexed by cluster name.
*/
global $wgExternalLoadBalancers;
$wgExternalLoadBalancers = array();
/**
* 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.
*/
global $wgExternalBlobCache;
$wgExternalBlobCache = array();
class ExternalStoreDB {
/** @todo Document.*/
function &getLoadBalancer( $cluster ) {
global $wgExternalServers, $wgExternalLoadBalancers;
if ( !array_key_exists( $cluster, $wgExternalLoadBalancers ) ) {
$wgExternalLoadBalancers[$cluster] = LoadBalancer::newFromParams( $wgExternalServers[$cluster] );
}
$wgExternalLoadBalancers[$cluster]->allowLagged(true);
return $wgExternalLoadBalancers[$cluster];
}
/** @todo Document.*/
function &getSlave( $cluster ) {
$lb =& $this->getLoadBalancer( $cluster );
return $lb->getConnection( DB_SLAVE );
}
/** @todo Document.*/
function &getMaster( $cluster ) {
$lb =& $this->getLoadBalancer( $cluster );
return $lb->getConnection( DB_MASTER );
}
/** @todo Document.*/
function getTable( &$db ) {
$table = $db->getLBInfo( 'blobs table' );
if ( is_null( $table ) ) {
$table = 'blobs';
}
return $table;
}
/**
* Fetch data from given URL
* @param string $url An url of the form DB://cluster/id or DB://cluster/id/itemid for concatened storage.
*/
function fetchFromURL($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 ) {
global $wgExternalBlobCache;
$cacheID = ( $itemID === false ) ? "$cluster/$id" : "$cluster/$id/";
if( isset( $wgExternalBlobCache[$cacheID] ) ) {
wfDebug( "ExternalStoreDB::fetchBlob cache hit on $cacheID\n" );
return $wgExternalBlobCache[$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 ) );
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 ) );
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 );
}
$wgExternalBlobCache = 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 ) {
$fname = 'ExternalStoreDB::store';
$dbw =& $this->getMaster( $cluster );
$id = $dbw->nextSequenceValue( 'blob_blob_id_seq' );
$dbw->insert( $this->getTable( $dbw ), array( 'blob_id' => $id, 'blob_text' => $data ), $fname );
$id = $dbw->insertId();
if ( $dbw->getFlag( DBO_TRX ) ) {
$dbw->immediateCommit();
}
return "DB://$cluster/$id";
}
}
?>
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