How to consume 100 messages without ack, then do work and then acknowledge them?

Question

I'm consuming messages from a rabbitmq with spring amqp. I'm consuming one message at a time and its pretty slow cause I save it to DB. So opening and closing transactions every time.

Right now I've set up a consumer like this.

@RabbitListener(queues = "queuename")
public void receive(Message message) {
 someservice.saveToDb(message);
}

But this is really slow. I would like to consume a bunch of messages before I start saving them. Then I can open a transaction. Save 300 and then commit and load the next batch.

Would something like this work?

class MessageChannelTag {
  Message message;
  Channel channel;
  long tag;
}

@Component
class ConsumerClass {

 List<MessageChannelTag> messagesToSave = new ArrayList<>();

 @RabbitListener(queues = "queuename")
 public void receive(Message message, Channel channel,  @Header(AmqpHeaders.DELIVERY_TAG) long tag)
            throws IOException {
    messagesToSave.add(new MessageChannelTag(message, channel, tag));
 }

 @Scheduled(fixedDelay=500)
 public void saveMessagesToDb() {
    List saveTheese = new ArrayList(messagesToSave);
    messagesToSave.clear();
    service.saveMessages(saveTheese);
    for(MessageChannelTag messageChannelTag:messagesToSave) {
    //In the service I could mark the rows if save succeded or not and
    //then out here I could ack or nack.. 

 messageChannelTag.getChannel().basicAck(messageChannelTag.getTag(), false);
    }
 }
}

Or if there is a simpler solution let me know. I prefer fast, simple and robust =)

Answer 1

如果“上游”生产者可以提供批量消息而不是单个消息，这也可能值得研究。

Answer 2

Don't use the "pull" API ( basic.get ), it is not nearly as efficient as consuming messages.

Set prefetch (also known as QoS) to 300, then acknowledge the messages at once when you are done. I am not familiar with Spring but I'm certain there are decorators or other ways to accomplish this.

This is all covered in the docs and tutorials - https://www.rabbitmq.com/consumer-prefetch.html

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