Merge "Made some FileBackendMultiWrite docs more accurate"

diff --combined includes/filebackend/FileBackendMultiWrite.php
index 6c6a90b,ba89204..fd6b844
--- 1/includes/filebackend/FileBackendMultiWrite.php
--- 2/includes/filebackend/FileBackendMultiWrite.php
+++ b/includes/filebackend/FileBackendMultiWrite.php
@@@ -33,14 -33,18 +33,16 @@@
   * Only use this class when transitioning from one storage system to another.
   *
   * Read operations are only done on the 'master' backend for consistency.
-  * Write operations are performed on all backends, in the order defined.
-  * If an operation fails on one backend it will be rolled back from the others.
+  * Write operations are performed on all backends, starting with the master.
+  * This makes a best-effort to have transactional semantics, but since requests
+  * may sometimes fail, the use of "autoResync" or background scripts to fix
+  * inconsistencies is important.
   *
   * @ingroup FileBackend
   * @since 1.19
   */
  class FileBackendMultiWrite extends FileBackend {
 -      /** @var array Prioritized list of FileBackendStore objects.
 -       * array of (backend index => backends)
 -       */
 +      /** @var FileBackendStore[] Prioritized list of FileBackendStore objects */
        protected $backends = array();
  
        /** @var int Index of master backend */
@@@ -686,6 -690,6 +688,6 @@@
                );
  
                // Actually acquire the locks
 -              return array( $this->getScopedFileLocks( $pbPaths, 'mixed', $status ) );
 +              return $this->getScopedFileLocks( $pbPaths, 'mixed', $status );
        }
  }