From eca50fb4b805495e6e946dc5e6a3c9a8f25357c9 Mon Sep 17 00:00:00 2001
From: Aaron Schulz <aaron@users.mediawiki.org>
Date: Mon, 25 Jul 2011 19:24:43 +0000
Subject: [PATCH] Follow-up r79518: added
 getCachedLastEditTime/getCachedLastEditTime methods to WikiPage and check
 them in loadPageData() to see if we should hit the master. This should lower
 the risk of stale data (by not just relying on cookie/session master position
 waiting).

---
 includes/WikiPage.php | 46 ++++++++++++++++++++++++++++++++++++-------
 1 file changed, 39 insertions(+), 7 deletions(-)

diff --git a/includes/WikiPage.php b/includes/WikiPage.php
index f6551aabfe..10b4809bd5 100644
--- a/includes/WikiPage.php
+++ b/includes/WikiPage.php
@@ -350,19 +350,28 @@ class WikiPage extends Page {
 	 *		A DB query result object or...
 	 *		"fromdb" to get from a slave DB or...
 	 *		"fromdbmaster" to get from the master DB
+	 * @return void
 	 */
 	public function loadPageData( $data = 'fromdb' ) {
-		if ( $data === 'fromdb' || $data === 'fromdbmaster' ) {
-			$db = ( $data == 'fromdbmaster' )
-				? wfGetDB( DB_MASTER )
-				: wfGetDB( DB_SLAVE );
-			$data = $this->pageDataFromTitle( $db, $this->mTitle );
+		if ( $data === 'fromdbmaster' ) {
+			$data = $this->pageDataFromTitle( wfGetDB( DB_MASTER ), $this->mTitle );
+		} elseif ( $data === 'fromdb' ) { // slave
+			$data = $this->pageDataFromTitle( wfGetDB( DB_SLAVE ), $this->mTitle );
+			# Use a "last rev inserted" timestamp key to dimish 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 ) ) {
+					$data = $this->pageDataFromTitle( wfGetDB( DB_MASTER ), $this->mTitle );
+				}
+			}
 		}
 
 		$lc = LinkCache::singleton();
 
 		if ( $data ) {
-			$lc->addGoodLinkObj( $data->page_id, $this->mTitle, $data->page_len, $data->page_is_redirect, $data->page_latest );
+			$lc->addGoodLinkObj( $data->page_id, $this->mTitle,
+				$data->page_len, $data->page_is_redirect, $data->page_latest );
 
 			$this->mTitle->loadFromRow( $data );
 
@@ -814,10 +823,11 @@ class WikiPage extends Page {
 			$conditions['page_latest'] = $lastRevision;
 		}
 
+		$now = wfTimestampNow();
 		$dbw->update( 'page',
 			array( /* SET */
 				'page_latest'      => $revision->getId(),
-				'page_touched'     => $dbw->timestamp(),
+				'page_touched'     => $dbw->timestamp( $now ),
 				'page_is_new'      => ( $lastRevision === 0 ) ? 1 : 0,
 				'page_is_redirect' => $rt !== null ? 1 : 0,
 				'page_len'         => strlen( $text ),
@@ -828,12 +838,34 @@ class WikiPage extends Page {
 		$result = $dbw->affectedRows() != 0;
 		if ( $result ) {
 			$this->updateRedirectOn( $dbw, $rt, $lastRevIsRedirect );
+			$this->setCachedLastEditTime( $now );
 		}
 
 		wfProfileOut( __METHOD__ );
 		return $result;
 	}
 
+	/**
+	 * Get the cached timestamp for the last time the page changed
+	 * @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
+	 * @param $timestamp string
+	 * @return void
+	 */
+	protected function setCachedLastEditTime( $timestamp ) {
+		global $wgMemc;
+		$key = wfMemcKey( 'page-lastedit', md5( $this->mTitle->getPrefixedDBkey() ) );
+		$wgMemc->set( $key, wfTimestamp( TS_MW, $timestamp ), 60*15 );
+	}
+
 	/**
 	 * Add row to the redirect table if this is a redirect, remove otherwise.
 	 *
-- 
2.20.1