From 57731929ab5ca9a77c2600509801b59606621ce0 Mon Sep 17 00:00:00 2001
From: Aaron Schulz <aschulz@wikimedia.org>
Date: Mon, 7 Apr 2014 15:18:19 -0700
Subject: [PATCH] Added limit to countRevisionsBetween() for sanity

* This was causing dozens of DB query timeout errors at WMF

Change-Id: Ie51a491ff5d22c2d84934e83d4b3f690c9dbd595
---
 includes/Title.php                 | 23 +++++++++++++++--------
 includes/diff/DifferenceEngine.php |  6 ++++--
 2 files changed, 19 insertions(+), 10 deletions(-)

diff --git a/includes/Title.php b/includes/Title.php
index d025f351c6..34ebf3a697 100644
--- a/includes/Title.php
+++ b/includes/Title.php
@@ -4343,7 +4343,7 @@ class Title {
 	 * @param int|Revision $new New revision or rev ID (first after range)
 	 * @return Int Number of revisions between these revisions.
 	 */
-	public function countRevisionsBetween( $old, $new ) {
+	public function countRevisionsBetween( $old, $new, $max = null ) {
 		if ( !( $old instanceof Revision ) ) {
 			$old = Revision::newFromTitle( $this, (int)$old );
 		}
@@ -4354,14 +4354,21 @@ class Title {
 			return 0; // nothing to compare
 		}
 		$dbr = wfGetDB( DB_SLAVE );
-		return (int)$dbr->selectField( 'revision', 'count(*)',
-			array(
-				'rev_page' => $this->getArticleID(),
-				'rev_timestamp > ' . $dbr->addQuotes( $dbr->timestamp( $old->getTimestamp() ) ),
-				'rev_timestamp < ' . $dbr->addQuotes( $dbr->timestamp( $new->getTimestamp() ) )
-			),
-			__METHOD__
+		$conds = array(
+			'rev_page' => $this->getArticleID(),
+			'rev_timestamp > ' . $dbr->addQuotes( $dbr->timestamp( $old->getTimestamp() ) ),
+			'rev_timestamp < ' . $dbr->addQuotes( $dbr->timestamp( $new->getTimestamp() ) )
 		);
+		if ( $max !== null ) {
+			$res = $dbr->select( 'revision', '1',
+				$conds,
+				__METHOD__,
+				array( 'LIMIT' => $max + 1 ) // extra to detect truncation
+			);
+			return $res->numRows();
+		} else {
+			return (int)$dbr->selectField( 'revision', 'count(*)', $conds, __METHOD__ );
+		}
 	}
 
 	/**
diff --git a/includes/diff/DifferenceEngine.php b/includes/diff/DifferenceEngine.php
index f77a4ebf75..3c4773e70e 100644
--- a/includes/diff/DifferenceEngine.php
+++ b/includes/diff/DifferenceEngine.php
@@ -970,8 +970,10 @@ class DifferenceEngine extends ContextSource {
 			$newRev = $this->mNewRev;
 		}
 
-		$nEdits = $this->mNewPage->countRevisionsBetween( $oldRev, $newRev );
-		if ( $nEdits > 0 ) {
+		// Sanity: don't show the notice if too many rows must be scanned
+		// @TODO: show some special message for that case
+		$nEdits = $this->mNewPage->countRevisionsBetween( $oldRev, $newRev, 1000 );
+		if ( $nEdits > 0 && $nEdits <= 1000 ) {
 			$limit = 100; // use diff-multi-manyusers if too many users
 			$users = $this->mNewPage->getAuthorsBetween( $oldRev, $newRev, $limit );
 			$numUsers = count( $users );
-- 
2.20.1