From ea44989fe4d1abf1508f9ebe9264c278ffcc3f35 Mon Sep 17 00:00:00 2001
From: Brion Vibber <brion@users.mediawiki.org>
Date: Tue, 27 Sep 2011 00:41:24 +0000
Subject: [PATCH] Debug logging and possible fix for bug 31177: mystery sidebar
 message failures

This may be related to things failing on load from External Storage; however we have not yet been able to verify this.

Tweaks MessageCache::loadFromDB() and MessageCache::getMsgFromNamespace() to avoid storing empty cache entries when loading text fails.
When building initial cache if we get a failure we'll log and store a '!TOO BIG' message which requests on-demand load later.
If an on-demand load failures, we'll log and return the false through but won't update the cache with the bad value.

To enable the logging in production, set up a $wgDebugLogFiles entry for 'MessageCache'.

Note that MessageCache::loadFromDB() bypasses Revision's text entry memcaching and may cause a lot of ES fetches at once.
However any ES failures *should* already be logged in the 'ExternalStoreDB' log file.
---
 includes/cache/MessageCache.php | 20 +++++++++++++++++---
 1 file changed, 17 insertions(+), 3 deletions(-)

diff --git a/includes/cache/MessageCache.php b/includes/cache/MessageCache.php
index 3f787e907f..59ee8c206d 100644
--- a/includes/cache/MessageCache.php
+++ b/includes/cache/MessageCache.php
@@ -428,7 +428,16 @@ class MessageCache {
 		);
 
 		foreach ( $res as $row ) {
-			$cache[$row->page_title] = ' ' . Revision::getRevisionText( $row );
+			$text = Revision::getRevisionText( $row );
+			if( $text === false ) {
+				// Failed to fetch data; possible ES errors?
+				// Store a marker to fetch on-demand as a workaround...
+				$entry = '!TOO BIG';
+				wfDebugLog( 'MessageCache', __METHOD__ . ": failed to load message page text for {$row->page_title} ($code)" );
+			} else {
+				$entry = ' ' . $text;
+			}
+			$cache[$row->page_title] = $entry;
 		}
 
 		foreach ( $mostused as $key ) {
@@ -741,8 +750,13 @@ class MessageCache {
 		$revision = Revision::newFromTitle( Title::makeTitle( NS_MEDIAWIKI, $title ) );
 		if ( $revision ) {
 			$message = $revision->getText();
-			$this->mCache[$code][$title] = ' ' . $message;
-			$this->mMemc->set( $titleKey, ' ' . $message, $this->mExpiry );
+			if ($message === false) {
+				// A possibly temporary loading failure.
+				wfDebugLog( 'MessageCache', __METHOD__ . ": failed to load message page text for {$title->getDbKey()} ($code)" );
+			} else {
+				$this->mCache[$code][$title] = ' ' . $message;
+				$this->mMemc->set( $titleKey, ' ' . $message, $this->mExpiry );
+			}
 		} else {
 			$message = false;
 			$this->mCache[$code][$title] = '!NONEXISTENT';
-- 
2.20.1