From: Brad Jorsch <bjorsch@wikimedia.org>
Date: Mon, 8 May 2017 18:00:26 +0000 (-0400)
Subject: MessageCache: Avoid 'contributions' replicas
X-Git-Tag: 1.31.0-rc.0~3295^2
X-Git-Url: http://git.cyclocoop.org/data/Fool?a=commitdiff_plain;h=6efee6f0dbe9340badbc973aa5fab8413f35a6a6;p=lhc%2Fweb%2Fwiklou.git

MessageCache: Avoid 'contributions' replicas

On WMF wikis, the partitioning of the revision table on the
'contributions' replicas makes the query here perform really poorly.
Specify 'api' as a hack for now to avoid those replicas.

This query happens once per day per wiki, plus when someone edits the
MediaWiki namespace, so it shouldn't be much additional load.

Bug: T164666
Change-Id: I5ae74d1702144f6475e9cfb13effc43389d66233
---

diff --git a/includes/cache/MessageCache.php b/includes/cache/MessageCache.php
index c992112068..8f88ee9e10 100644
--- a/includes/cache/MessageCache.php
+++ b/includes/cache/MessageCache.php
@@ -464,7 +464,11 @@ class MessageCache {
 	protected function loadFromDB( $code, $mode = null ) {
 		global $wgMaxMsgCacheEntrySize, $wgLanguageCode, $wgAdaptiveMessageCache;
 
-		$dbr = wfGetDB( ( $mode == self::FOR_UPDATE ) ? DB_MASTER : DB_REPLICA );
+		// (T164666) The query here performs really poorly on WMF's
+		// contributions replicas. We don't have a way to say "any group except
+		// contributions", so for the moment let's specify 'api'.
+		// @todo: Get rid of this hack.
+		$dbr = wfGetDB( ( $mode == self::FOR_UPDATE ) ? DB_MASTER : DB_REPLICA, 'api' );
 
 		$cache = [];