ApiQueryDeletedRevisions: Optimize ascending title generation

When generating titles rather than revids, it would be nice if we could
query with DISTINCT to get the titles directly instead of processing
every deleted revision for the title.

Sadly, it turns out this only works with dir=newer (dir=older is the
default). But that's probably better than nothing.

Bug: T110792
Change-Id: Idd300510c92b00722574d046399dbeb486afa98b

diff --git a/includes/api/ApiQueryAllDeletedRevisions.php b/includes/api/ApiQueryAllDeletedRevisions.php
index 4e4d2af..f802c95 100644 (file)
--- a/includes/api/ApiQueryAllDeletedRevisions.php
+++ b/includes/api/ApiQueryAllDeletedRevisions.php
@@ -83,6 +83,21 @@ class ApiQueryAllDeletedRevisions extends ApiQueryRevisionsBase {
                        }
                }
 
+               // If we're generating titles only, we can use DISTINCT for a better
+               // query. But we can't do that in 'user' mode (wrong index), and we can
+               // only do it when sorting ASC (because MySQL apparently can't use an
+               // index backwards for grouping even though it can for ORDER BY, WTF?)
+               $dir = $params['dir'];
+               $optimizeGenerateTitles = false;
+               if ( $mode === 'all' && $params['generatetitles'] && $resultPageSet !== null ) {
+                       if ( $dir === 'newer' ) {
+                               $optimizeGenerateTitles = true;
+                       } else {
+                               $p = $this->getModulePrefix();
+                               $this->setWarning( "For better performance when generating titles, set {$p}dir=newer" );
+                       }
+               }
+
                $this->addTables( 'archive' );
                if ( $resultPageSet === null ) {
                        $this->parseParameters( $params );
@@ -90,7 +105,12 @@ class ApiQueryAllDeletedRevisions extends ApiQueryRevisionsBase {
                        $this->addFields( array( 'ar_title', 'ar_namespace' ) );
                } else {
                        $this->limit = $this->getParameter( 'limit' ) ?: 10;
-                       $this->addFields( array( 'ar_title', 'ar_namespace', 'ar_timestamp', 'ar_rev_id', 'ar_id' ) );
+                       $this->addFields( array( 'ar_title', 'ar_namespace' ) );
+                       if ( $optimizeGenerateTitles ) {
+                               $this->addOption( 'DISTINCT' );
+                       } else {
+                               $this->addFields( array( 'ar_timestamp', 'ar_rev_id', 'ar_id' ) );
+                       }
                }
 
                if ( $this->fld_tags ) {
@@ -130,7 +150,6 @@ class ApiQueryAllDeletedRevisions extends ApiQueryRevisionsBase {
                        }
                }
 
-               $dir = $params['dir'];
                $miser_ns = null;
 
                if ( $mode == 'all' ) {
@@ -229,7 +248,14 @@ class ApiQueryAllDeletedRevisions extends ApiQueryRevisionsBase {
                if ( !is_null( $params['continue'] ) ) {
                        $cont = explode( '|', $params['continue'] );
                        $op = ( $dir == 'newer' ? '>' : '<' );
-                       if ( $mode == 'all' ) {
+                       if ( $optimizeGenerateTitles ) {
+                               $this->dieContinueUsageIf( count( $cont ) != 2 );
+                               $ns = intval( $cont[0] );
+                               $this->dieContinueUsageIf( strval( $ns ) !== $cont[0] );
+                               $title = $db->addQuotes( $cont[1] );
+                               $this->addWhere( "ar_namespace $op $ns OR " .
+                                       "(ar_namespace = $ns AND ar_title $op= $title)" );
+                       } elseif ( $mode == 'all' ) {
                                $this->dieContinueUsageIf( count( $cont ) != 4 );
                                $ns = intval( $cont[0] );
                                $this->dieContinueUsageIf( strval( $ns ) !== $cont[0] );
@@ -259,7 +285,13 @@ class ApiQueryAllDeletedRevisions extends ApiQueryRevisionsBase {
 
                $sort = ( $dir == 'newer' ? '' : ' DESC' );
                $orderby = array();
-               if ( $mode == 'all' ) {
+               if ( $optimizeGenerateTitles ) {
+                       // Targeting index name_title_timestamp
+                       if ( $params['namespace'] === null || count( array_unique( $params['namespace'] ) ) > 1 ) {
+                               $orderby[] = "ar_namespace $sort";
+                       }
+                       $orderby[] = "ar_title $sort";
+               } elseif ( $mode == 'all' ) {
                        // Targeting index name_title_timestamp
                        if ( $params['namespace'] === null || count( array_unique( $params['namespace'] ) ) > 1 ) {
                                $orderby[] = "ar_namespace $sort";
@@ -283,7 +315,9 @@ class ApiQueryAllDeletedRevisions extends ApiQueryRevisionsBase {
                foreach ( $res as $row ) {
                        if ( ++$count > $this->limit ) {
                                // We've had enough
-                               if ( $mode == 'all' ) {
+                               if ( $optimizeGenerateTitles ) {
+                                       $this->setContinueEnumParameter( 'continue', "$row->ar_namespace|$row->ar_title" );
+                               } elseif ( $mode == 'all' ) {
                                        $this->setContinueEnumParameter( 'continue',
                                                "$row->ar_namespace|$row->ar_title|$row->ar_timestamp|$row->ar_id"
                                        );