From a9aadaff39bd7d5684b05d829382300572ffee52 Mon Sep 17 00:00:00 2001
From: Aaron Schulz <aschulz@wikimedia.org>
Date: Mon, 30 Mar 2015 14:44:50 -0700
Subject: [PATCH] Removed "page-lastedit" cache key trick from WikiPage

* Just rely on chronology protected and edit conflict handling.
  The time a user spends looking at and editing pages is larger
  than any normal slave lag anyway.
* However make sure that pages just made in the request are visible.
* In "master" datacenters, the slave lag will low anyway, and
  callers make use of $flags when needed. In other datacenters,
  the cache will itself be subject to lag anyway.
* Logging (DBPerformance log) shows this case is very rarely
  hit anyway.

Change-Id: If34d67c02f9a7bf0a506ee8f3990697eb403a710
---
 includes/page/WikiPage.php | 38 ++++++--------------------------------
 1 file changed, 6 insertions(+), 32 deletions(-)

diff --git a/includes/page/WikiPage.php b/includes/page/WikiPage.php
index d96e2711c6..f2a3c799a8 100644
--- a/includes/page/WikiPage.php
+++ b/includes/page/WikiPage.php
@@ -367,14 +367,12 @@ class WikiPage implements Page, IDBAccessObject {
 			$data = $this->pageDataFromTitle( wfGetDB( DB_MASTER ), $this->mTitle );
 		} elseif ( $from === self::READ_NORMAL ) {
 			$data = $this->pageDataFromTitle( wfGetDB( DB_SLAVE ), $this->mTitle );
-			// Use a "last rev inserted" timestamp key to diminish the issue of slave lag.
-			// Note that DB also stores the master position in the session and checks it.
-			$touched = $this->getCachedLastEditTime();
-			if ( $touched ) { // key set
-				if ( !$data || $touched > wfTimestamp( TS_MW, $data->page_touched ) ) {
-					$from = self::READ_LATEST;
-					$data = $this->pageDataFromTitle( wfGetDB( DB_MASTER ), $this->mTitle );
-				}
+			if ( !$data
+				&& wfGetLB()->getServerCount() > 1
+				&& wfGetLB()->hasOrMadeRecentMasterChanges()
+			) {
+				$from = self::READ_LATEST;
+				$data = $this->pageDataFromTitle( wfGetDB( DB_MASTER ), $this->mTitle );
 			}
 		} else {
 			// No idea from where the caller got this data, assume slave database.
@@ -810,29 +808,6 @@ class WikiPage implements Page, IDBAccessObject {
 		}
 	}
 
-	/**
-	 * Get the cached timestamp for the last time the page changed.
-	 * This is only used to help handle slave lag by comparing to page_touched.
-	 * @return string MW timestamp
-	 */
-	protected function getCachedLastEditTime() {
-		global $wgMemc;
-		$key = wfMemcKey( 'page-lastedit', md5( $this->mTitle->getPrefixedDBkey() ) );
-		return $wgMemc->get( $key );
-	}
-
-	/**
-	 * Set the cached timestamp for the last time the page changed.
-	 * This is only used to help handle slave lag by comparing to page_touched.
-	 * @param string $timestamp
-	 * @return void
-	 */
-	public function setCachedLastEditTime( $timestamp ) {
-		global $wgMemc;
-		$key = wfMemcKey( 'page-lastedit', md5( $this->mTitle->getPrefixedDBkey() ) );
-		$wgMemc->set( $key, wfTimestamp( TS_MW, $timestamp ), 60 * 15 );
-	}
-
 	/**
 	 * Determine whether a page would be suitable for being counted as an
 	 * article in the site_stats table based on the title & its content
@@ -1304,7 +1279,6 @@ class WikiPage implements Page, IDBAccessObject {
 		if ( $result ) {
 			$this->updateRedirectOn( $dbw, $rt, $lastRevIsRedirect );
 			$this->setLastEdit( $revision );
-			$this->setCachedLastEditTime( $now );
 			$this->mLatest = $revision->getId();
 			$this->mIsRedirect = (bool)$rt;
 			// Update the LinkCache.
-- 
2.20.1