From e48fec5a8ab5916735849d420f2dfeec7eb0fced Mon Sep 17 00:00:00 2001
From: "Ori.livneh" <ori@wikimedia.org>
Date: Fri, 31 Jul 2015 23:13:35 +0000
Subject: [PATCH] Revert I4afaecd8: Avoiding writing sessions for no reason

I4afaecd8 reduced the frequency at which the TTL of sessions keys is reset, on
the assumption that we were doing it a whole lot more often than necessary.
We can now assume that this assumption was false, because an uncommitted revert
of this change which I pushed to production earlier caused the rate of session
loss errors in the logs to plummet.

Bug: T102199
Change-Id: Ie67f4ca000afcf3d4f44155c13f91cd4c286866d
---
 .../objectcache/ObjectCacheSessionHandler.php | 28 ++++---------------
 1 file changed, 5 insertions(+), 23 deletions(-)

diff --git a/includes/objectcache/ObjectCacheSessionHandler.php b/includes/objectcache/ObjectCacheSessionHandler.php
index ae3850f85c..1430dd8c3d 100644
--- a/includes/objectcache/ObjectCacheSessionHandler.php
+++ b/includes/objectcache/ObjectCacheSessionHandler.php
@@ -28,8 +28,6 @@
  * @ingroup Cache
  */
 class ObjectCacheSessionHandler {
-	/** @var array Map of (session ID => SHA-1 of the data) */
-	protected static $hashCache = array();
 
 	const TTL_REFRESH_WINDOW = 600; // refresh if expiring in 10 minutes
 
@@ -58,7 +56,6 @@ class ObjectCacheSessionHandler {
 	 */
 	protected static function getCache() {
 		global $wgSessionCacheType;
-
 		return ObjectCache::getInstance( $wgSessionCacheType );
 	}
 
@@ -72,14 +69,6 @@ class ObjectCacheSessionHandler {
 		return wfMemcKey( 'session', $id );
 	}
 
-	/**
-	 * @param mixed $data
-	 * @return string
-	 */
-	protected static function getHash( $data ) {
-		return sha1( serialize( $data ) );
-	}
-
 	/**
 	 * Callback when opening a session.
 	 *
@@ -109,10 +98,10 @@ class ObjectCacheSessionHandler {
 	 */
 	static function read( $id ) {
 		$data = self::getCache()->get( self::getKey( $id ) );
-
-		self::$hashCache = array( $id => self::getHash( $data ) );
-
-		return ( $data === false ) ? '' : $data;
+		if ( $data === false ) {
+			return '';
+		}
+		return $data;
 	}
 
 	/**
@@ -124,14 +113,7 @@ class ObjectCacheSessionHandler {
 	 */
 	static function write( $id, $data ) {
 		global $wgObjectCacheSessionExpiry;
-
-		// Only issue a write if anything changed (PHP 5.6 already does this)
-		if ( !isset( self::$hashCache[$id] )
-			|| self::getHash( $data ) !== self::$hashCache[$id]
-		) {
-			self::getCache()->set( self::getKey( $id ), $data, $wgObjectCacheSessionExpiry );
-		}
-
+		self::getCache()->set( self::getKey( $id ), $data, $wgObjectCacheSessionExpiry );
 		return true;
 	}
 
-- 
2.20.1