未处理java Google PubSub-resent消息

Question

我使用了google PubSub的google文档中的订户示例 我所做的唯一修改是注释掉消息的确认

订阅者不再向队列中添加消息，而应根据google云控制台中设置的间隔重新发送消息

为什么会发生这种情况，或者我遗漏了什么

public class SubscriberExample {

use the default project id
private static final String PROJECT_ID = ServiceOptions.getDefaultProjectId();

private static final BlockingQueue<PubsubMessage> messages = new LinkedBlockingDeque<>();

static class MessageReceiverExample implements MessageReceiver {



    @Override
    public void receiveMessage(PubsubMessage message, AckReplyConsumer consumer) {
        messages.offer(message);

        //consumer.ack();
    }
}
/** Receive messages over a subscription. */
public static void main(String[] args) throws Exception {
    // set subscriber id, eg. my-sub
    String subscriptionId = args[0];
    ProjectSubscriptionName subscriptionName = ProjectSubscriptionName.of(
            PROJECT_ID, subscriptionId);
    Subscriber subscriber = null;
    try {
        // create a subscriber bound to the asynchronous message receiver
        subscriber = Subscriber.newBuilder(subscriptionName, new MessageReceiverExample()).build();
        subscriber.startAsync().awaitRunning();
        // Continue to listen to messages
        while (true) {
            PubsubMessage message = messages.take();
            System.out.println("Message Id: " + message.getMessageId());
            System.out.println("Data: " + message.getData().toStringUtf8());
        }
    } finally {
       if (subscriber != null) {
            subscriber.stopAsync();
        }
    }
}
}

Answer 1

当您不确认消息时，Java客户端库将调用消息上的modifyAckDeadline，直到maxAckExtensionPeriod通过。默认情况下，此值为一小时。因此，如果您不确认/确认消息或更改此值，则消息可能在一小时内不会重新发送。如果要更改最大确认延长期，请在生成器上设置它：

subscriber = Subscriber.newBuilder(subscriptionName, new MessageReceiverExample())
    .setMaxAckExtensionPeriod(Duration.ofSeconds(60))
    .build();               

还值得注意的是，当您不确认或nack消息时，flow control可能会阻止更多消息的传递。默认情况下，Java客户端库允许多达1000条消息处于未完成状态，即等待ack或nack或等待max ack延长期的过去