@Override
    public Future<Void> set(final Map<ByteBuffer, ByteBuffer> values,
                            final Callback<Void> callback) {
        return executor.submit(() -> {
            data.putAll(values);
            save();
            if (callback != null)
                callback.onCompletion(null, null);
            return null;
        });
    }
Implementation of OffsetBackingStore that doesn't actually persist any data. To ensure this
behaves similarly to a real backing store, operations are executed asynchronously on a
background thread.
connect/runtime/src/main/java/org/apache/kafka/connect/storage/MemoryOffsetBackingStore.java