public static SubscriptionPollRequest deserialize(final ByteBuffer buffer) {
    final short requestType = ReadWriteIOUtils.readShort(buffer);
    SubscriptionPollPayload payload = null;
    if (SubscriptionPollRequestType.isValidatedRequestType(requestType)) {
      switch (SubscriptionPollRequestType.valueOf(requestType)) {
        case POLL:
          payload = new PollPayload().deserialize(buffer);
          break;
        case POLL_FILE:
          payload = new PollFilePayload().deserialize(buffer);
          break;
        case POLL_TABLETS:
          payload = new PollTabletsPayload().deserialize(buffer);
          break;
        default:
          LOGGER.warn("unexpected request type: {}, payload will be null", requestType);
          break;
      }
    } else {
      LOGGER.warn("unexpected request type: {}, payload will be null", requestType);
    }

    final long timeoutMs = ReadWriteIOUtils.readLong(buffer);
    final long maxBytes = ReadWriteIOUtils.readLong(buffer);
    return new SubscriptionPollRequest(requestType, payload, timeoutMs, maxBytes);
  }
The maximum size, in bytes, for the response payload.
iotdb-client/service-rpc/src/main/java/org/apache/iotdb/rpc/subscription/payload/poll/SubscriptionPollRequest.java