private function deleteSessions(array $sessions)
    {
        // gRPC calls appear to cancel when the corresponding UnaryCall object
        // goes out of scope. Keeping the calls in scope allows time for the
        // calls to complete at the expense of a small memory footprint.
        $this->deleteCalls = [];

        foreach ($sessions as $session) {
            $this->deleteCalls[] = $this->database->connection()
                ->deleteSessionAsync([
                    'name' => $session['name'],
                    'database' => $this->database->name()
                ]);
        }
    }