The messages in our system need to be processed in sequential (we expect the message to be handled one after another) and we are trying to build a queue consumer with the liberary solclientjs. ( solclientjs - npm > )
I read some blogs and posts that mentioned two keywords the flow windowSize and MAX_UNACKNOWLEDGED_MESSSAGES.
fristly, I have tried to reduce the windowSize to 1 and leave the MAX_DELIVERED_UNACKNOWLEDGED_MSGS_PER_FLOW as default with below sample code and saw the incoming messages are processed almost sententiously.
// consumer generation logic
this.messageConsumer = this.session.createMessageConsumer({
queueDescriptor: new QueueDescriptor({
name: this.consumerOptions?.queueName as string,
type: QueueType.QUEUE
}),
acknowledgeMode: MessageConsumerAcknowledgeMode.CLIENT,
activeIndicationEnabled: true,
windowSize: 1 // set the windownSize here
});
// process logic
// have noticed that the handler function is not async/Promise by the typscript definition
//
// [solace.MessageConsumerEventName.MESSAGE]: (
// message: solace.Message
// ) => void;
this.messageConsumer?.on(MessageConsumerEventName.MESSAGE, async (message) => {
const messageBody = this.decoder.decode(message.getBinaryAttachment());
const sleepInSec = _.random(5, 10);
logger.info(${messageBody} arrived, simulate process ${sleepInSec}s);
await sleep(sleepInSec * 1000);
message.acknowledge();
logger.info(${messageBody} acknowledged);
});
// log [2022-03-30T16:48:00.021Z] [info]: message[0] arrived, simulate process 6s [2022-03-30T16:48:00.028Z] [info]: message[1] arrived, simulate process 8s [2022-03-30T16:48:00.033Z] [info]: message[2] arrived, simulate process 5s [2022-03-30T16:48:00.046Z] [info]: message[3] arrived, simulate process 8s [2022-03-30T16:48:00.061Z] [info]: message[4] arrived, simulate process 5s [2022-03-30T16:48:05.048Z] [info]: message[2] acknowledged [2022-03-30T16:48:05.064Z] [info]: message[4] acknowledged [2022-03-30T16:48:06.028Z] [info]: message[0] acknowledged [2022-03-30T16:48:08.044Z] [info]: message[1] acknowledged [2022-03-30T16:48:08.059Z] [info]: message[3] acknowledged additionally I adjusted the MAX_DELIVERED_UNACKNOWLEDGED_MSGS_PER_FLOW to 1 in the queue config, then looks the consumer behavior is expected.
// log [2022-03-30T17:34:04.099Z] [info]: message[0] arrived, simulate process 9s [2022-03-30T17:34:13.101Z] [info]: message[0] acknowledged [2022-03-30T17:34:14.111Z] [info]: message[1] arrived, simulate process 5s [2022-03-30T17:34:19.117Z] [info]: message[1] acknowledged [2022-03-30T17:34:20.127Z] [info]: message[2] arrived, simulate process 9s [2022-03-30T17:34:29.137Z] [info]: message[2] acknowledged [2022-03-30T17:34:30.149Z] [info]: message[3] arrived, simulate process 6s [2022-03-30T17:34:36.154Z] [info]: message[3] acknowledged [2022-03-30T17:34:37.168Z] [info]: message[4] arrived, simulate process 9s [2022-03-30T17:34:46.185Z] [info]: message[4] acknowledged And I feel like it is not a recommended to do this by adjust the MAX_UNACKNOWLEDGED_MESSAGES setting.
Trying to understand Consumer Ack Window — Solace Community It is not flow control. Withholding acknowledgements will not stop the broker from sending more messages. You can simulate flow control by reducing MAX_UNACKNOWLEDGED_MESSSAGES on the endpoint to a point where the application can stop message flow by withholding acknowledgements. However that is a blunt hammer to solve this. MAX_UNACKNOWLEDGED_MESSAGES is intended to prevent one receiver from consuming too many resources. It is not intended for flow control. Then I have a little bit confused and have a few questions here.
- it there any recommended way to archive the behavior that only one message is pushed to the handler function?
2 ) when the event MessageConsumerEventName.MESSAGE emitted? is it the time a consumer received an unacknowledged message from the broker? - any performance downgrades by setting MAX_UNACKNOWLEDGED_MESSAGES = 1?
Thanks
Ref articles:
https://solace.com/blog/configuring-pre-fetch-for-optimized-load-balancing/ Trying to understand Consumer Ack Window — Solace Community ClientAck behavior in case ack is not sent (timeout) — Solace Community