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 193f20f..4775b96 100644 (file)
--- 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'];