private function incrementalSync(PollTask $currentTask, $usnChangedStartFrom, $highestCommitedUSN)
    {
        list($changed, $deleted) = $this->fetcher->incrementalFetch($usnChangedStartFrom, $highestCommitedUSN, $this->detectDeleted);
        $this->synchronizer->incrementalSync($this->name, $currentTask->getId(), $changed, $deleted);
        $this->logIncrementalSync($changed, $deleted);

        return count($changed) + count($deleted);
    }