From: Aaron Schulz <aschulz@wikimedia.org>
Date: Wed, 20 Apr 2016 19:37:00 +0000 (-0700)
Subject: Make MessageCache handle lock timeouts better
X-Git-Tag: 1.31.0-rc.0~7226
X-Git-Url: https://git.heureux-cyclage.org/?a=commitdiff_plain;h=2cafd151de7439170550dc0604c7776f5279468a;p=lhc%2Fweb%2Fwiklou.git

Make MessageCache handle lock timeouts better

* Timeouts happen when memcached is cleared or on DC-switchover likewise
* Disable the sidebar cache when the MessageCache is disabled
* Also lower any output expiry for CDN and set a custom header
  when the MessageCache is disabled
* Log when this happens to a dedicated "MessageCacheError" channel

Bug: T133069
Bug: T7092
Change-Id: I1b80e250532033c52680246279e1e8f56350ae83
---

diff --git a/includes/DefaultSettings.php b/includes/DefaultSettings.php
index 10e6adbe48..f2370ad2e0 100644
--- a/includes/DefaultSettings.php
+++ b/includes/DefaultSettings.php
@@ -2589,6 +2589,13 @@ $wgCdnMaxageLagged = 30;
  */
 $wgCdnReboundPurgeDelay = 0;
 
+/**
+ * Cache timeout for the CDN when a response is known to be wrong or incomplete (due to load)
+ * @see $wgSquidMaxage
+ * @since 1.27
+ */
+$wgCdnMaxageSubstitute = 60;
+
 /**
  * Default maximum age for raw CSS/JS accesses
  *
diff --git a/includes/MediaWiki.php b/includes/MediaWiki.php
index ad02e68bb5..3dd7420b88 100644
--- a/includes/MediaWiki.php
+++ b/includes/MediaWiki.php
@@ -585,6 +585,13 @@ class MediaWiki {
 			$request->response()->header( "X-Database-Lagged: true" );
 			wfDebugLog( 'replication', "Lagged DB used; CDN cache TTL limited to $maxAge seconds" );
 		}
+
+		// Avoid long-term cache pollution due to message cache rebuild timeouts (T133069)
+		if ( MessageCache::singleton()->isDisabled() ) {
+			$maxAge = $config->get( 'CdnMaxageSubstitute' );
+			$context->getOutput()->lowerCdnMaxage( $maxAge );
+			$request->response()->header( "X-Response-Substitute: true" );
+		}
 	}
 
 	/**
diff --git a/includes/cache/MessageCache.php b/includes/cache/MessageCache.php
index 0e566eaf3b..62fab5fc50 100644
--- a/includes/cache/MessageCache.php
+++ b/includes/cache/MessageCache.php
@@ -51,7 +51,7 @@ class MessageCache {
 	protected $mCache;
 
 	/**
-	 * Should  mean that database cannot be used, but check
+	 * Should mean that database cannot be used, but check
 	 * @var bool $mDisable
 	 */
 	protected $mDisable;
@@ -355,6 +355,7 @@ class MessageCache {
 			$where[] = 'loading FAILED - cache is disabled';
 			$this->mDisable = true;
 			$this->mCache = false;
+			wfDebugLog( 'MessageCacheError', __METHOD__ . ": Failed to load $code\n" );
 			# This used to throw an exception, but that led to nasty side effects like
 			# the whole wiki being instantly down if the memcached server died
 		} else {
@@ -1113,6 +1114,22 @@ class MessageCache {
 		$this->mDisable = false;
 	}
 
+	/**
+	 * Whether DB/cache usage is disabled for determining messages
+	 *
+	 * If so, this typically indicates either:
+	 *   - a) load() failed to find a cached copy nor query the DB
+	 *   - b) we are in a special context or error mode that cannot use the DB
+	 * If the DB is ignored, any derived HTML output or cached objects may be wrong.
+	 * To avoid long-term cache pollution, TTLs can be adjusted accordingly.
+	 *
+	 * @return bool
+	 * @since 1.27
+	 */
+	public function isDisabled() {
+		return $this->mDisable;
+	}
+
 	/**
 	 * Clear all stored messages. Mainly used after a mass rebuild.
 	 */
diff --git a/includes/skins/Skin.php b/includes/skins/Skin.php
index 4d7fc50c4d..04cf351ff7 100644
--- a/includes/skins/Skin.php
+++ b/includes/skins/Skin.php
@@ -1200,7 +1200,9 @@ abstract class Skin extends ContextSource {
 			$cache = ObjectCache::getMainWANInstance();
 			$sidebar = $cache->getWithSetCallback(
 				$cache->makeKey( 'sidebar', $this->getLanguage()->getCode() ),
-				$wgSidebarCacheExpiry,
+				MessageCache::singleton()->isDisabled()
+					? $cache::TTL_UNCACHEABLE // bug T133069
+					: $wgSidebarCacheExpiry,
 				$callback,
 				[ 'lockTSE' => 30 ]
 			);