From 187fd647232a1887c202d3624a5b8e7c7f674093 Mon Sep 17 00:00:00 2001
From: Aaron Schulz <aschulz@wikimedia.org>
Date: Fri, 8 May 2015 22:20:25 -0700
Subject: [PATCH] Made triggerOpportunisticLinksUpdate() jobs make use of
 parser cache

* On Wikipedia, for example, these jobs are good percent of
  all refreshLinks jobs; skipping the parse step should avoid
  runner CPU overhead
* Also fixed bad TS_MW/TS_UNIX comparison
* Moved the fudge factor to a constant and raised it a bit

Bug: T98621
Change-Id: Id6d64972739df4b26847e4374f30ddcc7f93b54a
---
 includes/jobqueue/jobs/RefreshLinksJob.php | 32 +++++++++++++++++-----
 includes/page/WikiPage.php                 |  3 ++
 2 files changed, 28 insertions(+), 7 deletions(-)

diff --git a/includes/jobqueue/jobs/RefreshLinksJob.php b/includes/jobqueue/jobs/RefreshLinksJob.php
index 1252b0b5e2..749913aef7 100644
--- a/includes/jobqueue/jobs/RefreshLinksJob.php
+++ b/includes/jobqueue/jobs/RefreshLinksJob.php
@@ -37,6 +37,8 @@
 class RefreshLinksJob extends Job {
 	const PARSE_THRESHOLD_SEC = 1.0;
 
+	const CLOCK_FUDGE = 10;
+
 	function __construct( $title, $params = '' ) {
 		parent::__construct( 'refreshLinks', $title, $params );
 		// A separate type is used just for cascade-protected backlinks
@@ -140,22 +142,38 @@ class RefreshLinksJob extends Job {
 
 		$parserOutput = false;
 		$parserOptions = $page->makeParserOptions( 'canonical' );
-		// If page_touched changed after this root job (with a good slave lag skew factor),
-		// then it is likely that any views of the pages already resulted in re-parses which
-		// are now in cache. This can be reused to avoid expensive parsing in some cases.
+		// If page_touched changed after this root job, then it is likely that
+		// any views of the pages already resulted in re-parses which are now in
+		// cache. The cache can be reused to avoid expensive parsing in some cases.
 		if ( isset( $this->params['rootJobTimestamp'] ) ) {
-			$skewedTimestamp = wfTimestamp( TS_UNIX, $this->params['rootJobTimestamp'] ) + 5;
-			if ( $page->getLinksTimestamp() > wfTimestamp( TS_MW, $skewedTimestamp ) ) {
+			$opportunistic = !empty( $this->params['isOpportunistic'] );
+
+			$skewedTimestamp = $this->params['rootJobTimestamp'];
+			if ( $opportunistic ) {
+				// Neither clock skew nor DB snapshot/slave lag matter much for such
+				// updates; focus on reusing the (often recently updated) cache
+			} else {
+				// For transclusion updates, the template changes must be reflected
+				$skewedTimestamp = wfTimestamp( TS_MW,
+					wfTimestamp( TS_UNIX, $skewedTimestamp ) + self::CLOCK_FUDGE
+				);
+			}
+
+			if ( $page->getLinksTimestamp() > $skewedTimestamp ) {
 				// Something already updated the backlinks since this job was made
 				return true;
 			}
-			if ( $page->getTouched() > wfTimestamp( TS_MW, $skewedTimestamp ) ) {
+
+			if ( $page->getTouched() >= $skewedTimestamp || $opportunistic ) {
+				// Something bumped page_touched since this job was made
+				// or the cache is otherwise suspected to be up-to-date
 				$parserOutput = ParserCache::singleton()->getDirty( $page, $parserOptions );
-				if ( $parserOutput && $parserOutput->getCacheTime() <= $skewedTimestamp ) {
+				if ( $parserOutput && $parserOutput->getCacheTime() < $skewedTimestamp ) {
 					$parserOutput = false; // too stale
 				}
 			}
 		}
+
 		// Fetch the current revision and parse it if necessary...
 		if ( $parserOutput == false ) {
 			$start = microtime( true );
diff --git a/includes/page/WikiPage.php b/includes/page/WikiPage.php
index cc182a4258..7b33b02e71 100644
--- a/includes/page/WikiPage.php
+++ b/includes/page/WikiPage.php
@@ -3411,6 +3411,9 @@ class WikiPage implements Page, IDBAccessObject {
 
 		// Check if the last link refresh was before page_touched
 		if ( $this->getLinksTimestamp() < $this->getTouched() ) {
+			$params['isOpportunistic'] = true;
+			$params['rootJobTimestamp'] = $parserOutput->getCacheTime();
+
 			JobQueueGroup::singleton()->push( EnqueueJob::newFromLocalJobs(
 				new JobSpecification( 'refreshLinks', $params,
 					array( 'removeDuplicates' => true ), $this->mTitle )
-- 
2.20.1