From: Aaron Schulz <aschulz@wikimedia.org>
Date: Sat, 9 Nov 2013 20:33:59 +0000 (-0800)
Subject: BacklinkCache performance tweaks
X-Git-Tag: 1.31.0-rc.0~18163^2
X-Git-Url: http://git.cyclocoop.org/%22%2C%20generer_url_ecrire%28?a=commitdiff_plain;h=a9dc4d943e8f7e7824f31dc7fd1270873f8a9fdb;p=lhc%2Fweb%2Fwiklou.git

BacklinkCache performance tweaks

* In partition(), avoid doing the JOIN since it is not needed and prevents
  index-only queries.
* Made numLinks() wrap partition when no $max is specified.
* Also fixed some docs

Change-Id: I05a83f71efb4c6e99e40883d7fa53da59184b13c
---

diff --git a/includes/cache/BacklinkCache.php b/includes/cache/BacklinkCache.php
index 193f20fee8..4775b96a9c 100644
--- a/includes/cache/BacklinkCache.php
+++ b/includes/cache/BacklinkCache.php
@@ -48,6 +48,7 @@ class BacklinkCache {
 	/**
 	 * Multi dimensions array representing batches. Keys are:
 	 *  > (string) links table name
+	 *   > (int) batch size
 	 *    > 'numRows' : Number of rows for this link table
 	 *    > 'batches' : array( $start, $end )
 	 *
@@ -169,9 +170,10 @@ class BacklinkCache {
 	 * @param $startId Integer|false
 	 * @param $endId Integer|false
 	 * @param $max Integer|INF
+	 * @param $select string 'all' or 'ids'
 	 * @return ResultWrapper
 	 */
-	protected function queryLinks( $table, $startId, $endId, $max ) {
+	protected function queryLinks( $table, $startId, $endId, $max, $select = 'all' ) {
 		wfProfileIn( __METHOD__ );
 
 		$fromField = $this->getPrefix( $table ) . '_from';
@@ -192,18 +194,32 @@ class BacklinkCache {
 			if ( $endId ) {
 				$conds[] = "$fromField <= " . intval( $endId );
 			}
-			$options = array( 'STRAIGHT_JOIN', 'ORDER BY' => $fromField );
+			$options = array( 'ORDER BY' => $fromField );
 			if ( is_finite( $max ) && $max > 0 ) {
 				$options['LIMIT'] = $max;
 			}
 
-			$res = $this->getDB()->select(
-				array( $table, 'page' ),
-				array( 'page_namespace', 'page_title', 'page_id' ),
-				$conds,
-				__METHOD__,
-				$options
-			);
+			if ( $select === 'ids' ) {
+				// Just select from the backlink table and ignore the page JOIN
+				$res = $this->getDB()->select(
+					$table,
+					array( $this->getPrefix( $table ) . '_from AS page_id' ),
+					array_filter( $conds, function( $clause ) { // kind of janky
+						return !preg_match( '/(\b|=)page_id(\b|=)/', $clause );
+					} ),
+					__METHOD__,
+					$options
+				);
+			} else {
+				// Select from the backlink table and JOIN with page title information
+				$res = $this->getDB()->select(
+					array( $table, 'page' ),
+					array( 'page_namespace', 'page_title', 'page_id' ),
+					$conds,
+					__METHOD__,
+					array_merge( array( 'STRAIGHT_JOIN' ), $options )
+				);
+			}
 
 			if ( !$startId && !$endId && $res->numRows() < $max ) {
 				// The full results fit within the limit, so cache them
@@ -280,13 +296,13 @@ class BacklinkCache {
 			case 'imagelinks':
 				$conds = array(
 					'il_to' => $this->title->getDBkey(),
-					'page_id=il_from'
+					"page_id={$prefix}_from"
 				);
 				break;
 			case 'categorylinks':
 				$conds = array(
 					'cl_to' => $this->title->getDBkey(),
-					'page_id=cl_from',
+					"page_id={$prefix}_from"
 				);
 				break;
 			default:
@@ -316,7 +332,7 @@ class BacklinkCache {
 	 * @return integer
 	 */
 	public function getNumLinks( $table, $max = INF ) {
-		global $wgMemc;
+		global $wgMemc, $wgUpdateRowsPerJob;
 
 		// 1) try partition cache ...
 		if ( isset( $this->partitionCache[$table] ) ) {
@@ -338,9 +354,17 @@ class BacklinkCache {
 		}
 
 		// 4) fetch from the database ...
-		$count = $this->getLinks( $table, false, false, $max )->count();
-		if ( $count < $max ) { // full count
-			$wgMemc->set( $memcKey, $count, self::CACHE_EXPIRY );
+		if ( is_infinite( $max ) ) { // no limit at all
+			// Use partition() since it will batch the query and skip the JOIN.
+			// Use $wgUpdateRowsPerJob just to encourage cache reuse for jobs.
+			$this->partition( $table, $wgUpdateRowsPerJob ); // updates $this->partitionCache
+			return $this->partitionCache[$table][$wgUpdateRowsPerJob]['numRows'];
+		} else { // probably some sane limit
+			// Fetch the full title info, since the caller will likely need it next
+			$count = $this->getLinks( $table, false, false, $max )->count();
+			if ( $count < $max ) { // full count
+				$wgMemc->set( $memcKey, $count, self::CACHE_EXPIRY );
+			}
 		}
 
 		return min( $max, $count );
@@ -396,7 +420,7 @@ class BacklinkCache {
 		$selectSize = max( $batchSize, 200000 - ( 200000 % $batchSize ) );
 		$start = false;
 		do {
-			$res = $this->queryLinks( $table, $start, false, $selectSize );
+			$res = $this->queryLinks( $table, $start, false, $selectSize, 'ids' );
 			$partitions = $this->partitionResult( $res, $batchSize, false );
 			// Merge the link count and range partitions for this chunk
 			$cacheEntry['numRows'] += $partitions['numRows'];