Avoiding writing sessions for no reason

bug: T88635
Change-Id: I4afaecd8dc29390b1ee2a6a77f9ca0cba333ef92

diff --git a/includes/objectcache/ObjectCacheSessionHandler.php b/includes/objectcache/ObjectCacheSessionHandler.php
index 40b40d1..24d2a22 100644 (file)
--- a/includes/objectcache/ObjectCacheSessionHandler.php
+++ b/includes/objectcache/ObjectCacheSessionHandler.php
@@ -28,6 +28,9 @@
  * @ingroup Cache
  */
 class ObjectCacheSessionHandler {
+       /** @var array Map of (session ID => SHA-1 of the data) */
+       protected static $hashCache = array();
+
        /**
         * Install a session handler for the current web request
         */
@@ -51,8 +54,9 @@ class ObjectCacheSessionHandler {
         * Get the cache storage object to use for session storage
         * @return BagOStuff
         */
-       static function getCache() {
+       protected static function getCache() {
                global $wgSessionCacheType;
+
                return ObjectCache::getInstance( $wgSessionCacheType );
        }
 
@@ -62,10 +66,18 @@ class ObjectCacheSessionHandler {
         * @param string $id Session id
         * @return string Cache key
         */
-       static function getKey( $id ) {
+       protected static function getKey( $id ) {
                return wfMemcKey( 'session', $id );
        }
 
+       /**
+        * @param mixed $data
+        * @return string
+        */
+       protected static function getHash( $data ) {
+               return sha1( serialize( $data ) );
+       }
+
        /**
         * Callback when opening a session.
         *
@@ -95,10 +107,10 @@ class ObjectCacheSessionHandler {
         */
        static function read( $id ) {
                $data = self::getCache()->get( self::getKey( $id ) );
-               if ( $data === false ) {
-                       return '';
-               }
-               return $data;
+
+               self::$hashCache = array( $id => self::getHash( $data ) );
+
+               return ( $data === false ) ? '' : $data;
        }
 
        /**
@@ -110,7 +122,14 @@ class ObjectCacheSessionHandler {
         */
        static function write( $id, $data ) {
                global $wgObjectCacheSessionExpiry;
-               self::getCache()->set( self::getKey( $id ), $data, $wgObjectCacheSessionExpiry );
+
+               // Only issue a write if anything changed (PHP 5.6 already does this)
+               if ( !isset( self::$hashCache[$id] )
+                       || self::getHash( $data ) !== self::$hashCache[$id]
+               ) {
+                       self::getCache()->set( self::getKey( $id ), $data, $wgObjectCacheSessionExpiry );
+               }
+
                return true;
        }
 
@@ -122,6 +141,7 @@ class ObjectCacheSessionHandler {
         */
        static function destroy( $id ) {
                self::getCache()->delete( self::getKey( $id ) );
+
                return true;
        }