Merge "cache: Minor docs for MessageCache interaction with WANObjectCache"

diff --git a/includes/cache/MessageCache.php b/includes/cache/MessageCache.php
index 59486e4..48aac7e 100644 (file)
--- a/includes/cache/MessageCache.php
+++ b/includes/cache/MessageCache.php
@@ -592,13 +592,15 @@ class MessageCache {
                                                [ 'title' => $title, 'code' => $code ] );
                                        return;
                                }
-                               // Load the messages from the master DB to avoid race conditions
+                               // Reload messages from the database and pre-populate dc-local caches
+                               // as optimisation. Use the master DB to avoid race conditions.
                                $cache = $this->loadFromDB( $code, self::FOR_UPDATE );
                                // Check if an individual cache key should exist and update cache accordingly
                                $page = WikiPage::factory( Title::makeTitle( NS_MEDIAWIKI, $title ) );
                                $page->loadPageData( $page::READ_LATEST );
                                $text = $this->getMessageTextFromContent( $page->getContent() );
                                if ( is_string( $text ) && strlen( $text ) > $wgMaxMsgCacheEntrySize ) {
+                                       // Match logic of loadCachedMessagePageEntry()
                                        $this->wanCache->set(
                                                $this->bigMessageCacheKey( $cache['HASH'], $title ),
                                                ' ' . $text,
@@ -1037,6 +1039,8 @@ class MessageCache {
                                $title = Title::makeTitle( NS_MEDIAWIKI, $dbKey );
                                $revision = Revision::newKnownCurrent( $dbr, $title );
                                if ( !$revision ) {
+                                       // The wiki doesn't have a local override page. Cache absence with normal TTL.
+                                       // When overrides are created, self::replace() takes care of the cache.
                                        return '!NONEXISTENT';
                                }
                                $content = $revision->getContent();
@@ -1050,13 +1054,14 @@ class MessageCache {
                                        $message = null;
                                }
 
-                               if ( is_string( $message ) ) {
-                                       return ' ' . $message;
+                               if ( !is_string( $message ) ) {
+                                       // Revision failed to load Content, or Content is incompatible with wikitext.
+                                       // Possibly a temporary loading failure.
+                                       $ttl = 5;
+                                       return '!NONEXISTENT';
                                }
 
-                               $ttl = 5; // possibly a temporary loading failure
-
-                               return '!NONEXISTENT';
+                               return ' ' . $message;
                        }
                );
        }