MessageCache: some inline comments

Change-Id: I42427eef73d86c1a2e99dfa22b5dae159542e243

diff --git a/includes/cache/MessageCache.php b/includes/cache/MessageCache.php
index 0c2f9de..4e6b2fd 100644 (file)
--- a/includes/cache/MessageCache.php
+++ b/includes/cache/MessageCache.php
@@ -496,6 +496,7 @@ class MessageCache {
                        if ( $text === false ) {
                                // Failed to fetch data; possible ES errors?
                                // Store a marker to fetch on-demand as a workaround...
+                               // TODO Use a differnt marker
                                $entry = '!TOO BIG';
                                wfDebugLog(
                                        'MessageCache',
@@ -510,6 +511,10 @@ class MessageCache {
 
                $cache['VERSION'] = MSG_CACHE_VERSION;
                ksort( $cache );
+
+               # Hash for validating local cache (APC). No need to take into account
+               # messages larger than $wgMaxMsgCacheEntrySize, since those are only
+               # stored and fetched from memcache.
                $cache['HASH'] = md5( serialize( $cache ) );
                $cache['EXPIRY'] = wfTimestamp( TS_MW, time() + $this->mExpiry );
 
@@ -568,7 +573,8 @@ class MessageCache {
                }
 
                ScopedCallback::consume( $scopedLock );
-               // Relay the purge to APC and other DCs
+               // Relay the purge. Touching this check key expires cache contents
+               // and local cache (APC) validation hash across all datacenters.
                $this->wanCache->touchCheckKey( wfMemcKey( 'messages', $code ) );
 
                // Also delete cached sidebar... just in case it is affected