From 04103860a2baaf847ad017d1bb91edd4a0ad00ba Mon Sep 17 00:00:00 2001
From: Aaron Schulz <aschulz@wikimedia.org>
Date: Wed, 13 Apr 2016 10:54:28 -0700
Subject: [PATCH] Allow description text caching for ForeignDBFile

A large amount of real time is spent in fetching Commons
descriptions pages from wikipedias, according to xenon
flame graphs.

Change-Id: I3935bf8bf23da58b734f897d7a1979e9b2f7e5c8
---
 includes/filerepo/file/ForeignDBFile.php | 59 +++++++++++++++++++++---
 1 file changed, 53 insertions(+), 6 deletions(-)

diff --git a/includes/filerepo/file/ForeignDBFile.php b/includes/filerepo/file/ForeignDBFile.php
index f38248b52b..cf0045e43f 100644
--- a/includes/filerepo/file/ForeignDBFile.php
+++ b/includes/filerepo/file/ForeignDBFile.php
@@ -124,8 +124,51 @@ class ForeignDBFile extends LocalFile {
 	 * @return string
 	 */
 	function getDescriptionText( $lang = false ) {
-		// Restore remote behavior
-		return File::getDescriptionText( $lang );
+		global $wgLang;
+
+		if ( !$this->repo->fetchDescription ) {
+			return false;
+		}
+
+		$lang = $lang ?: $wgLang;
+		$renderUrl = $this->repo->getDescriptionRenderUrl( $this->getName(), $lang->getCode() );
+		if ( !$renderUrl ) {
+			return false;
+		}
+
+		$touched = $this->repo->getSlaveDB()->selectField(
+			'page',
+			'page_touched',
+			[
+				'page_namespace' => NS_FILE,
+				'page_title' => $this->title->getDBkey()
+			]
+		);
+		if ( $touched === false ) {
+			return false; // no description page
+		}
+
+		$cache = ObjectCache::getMainWANInstance();
+
+		return $cache->getWithSetCallback(
+			$this->repo->getLocalCacheKey(
+				'RemoteFileDescription',
+				'url',
+				$lang->getCode(),
+				$this->getName(),
+				$touched
+			),
+			$this->repo->descriptionCacheExpiry ?: $cache::TTL_UNCACHEABLE,
+			function ( $oldValue, &$ttl, array &$setOpts ) use ( $renderUrl ) {
+				wfDebug( "Fetching shared description from $renderUrl\n" );
+				$res = Http::get( $renderUrl, [], __METHOD__ );
+				if ( !$res ) {
+					$ttl = WANObjectCache::TTL_UNCACHEABLE;
+				}
+
+				return $res;
+			}
+		);
 	}
 
 	/**
@@ -137,10 +180,14 @@ class ForeignDBFile extends LocalFile {
 	 */
 	public function getDescriptionShortUrl() {
 		$dbr = $this->repo->getSlaveDB();
-		$pageId = $dbr->selectField( 'page', 'page_id', [
-			'page_namespace' => NS_FILE,
-			'page_title' => $this->title->getDBkey()
-		] );
+		$pageId = $dbr->selectField(
+			'page',
+			'page_id',
+			[
+				'page_namespace' => NS_FILE,
+				'page_title' => $this->title->getDBkey()
+			]
+		);
 
 		if ( $pageId !== false ) {
 			$url = $this->repo->makeUrl( [ 'curid' => $pageId ] );
-- 
2.20.1