Google pubsub golang subscriber stops receiving ne

问题:

I created a TOPIC in google pubsub, and created a SUBSCRIPTION inside the TOPIC, with the following settings

then I wrote a puller in go, using its Receive to pull and acknowledge published messages

package main

import (
    ...
)

func main() {
    ctx := context.Background()

    client, err := pubsub.NewClient(ctx, config.C.Project)
    if err != nil {
       // do things with err
    }
    sub := client.Subscription(config.C.PubsubSubscription)
    err := sub.Receive(ctx, func(ctx context.Context, msg *pubsub.Message) {
        msg.Ack()
    })

    if err != context.Canceled {
      logger.Error(fmt.Sprintf("Cancelled: %s", err.Error()))
    }
    if err != nil {
      logger.Error(fmt.Sprintf("Error: %s", err.Error()))
    }
  }

Nothing fancy, its working well, but then after a while (~ after 3 hours idle), it stops receiving new published messages, no error(s), nothing. Am i missing something?

回答1:

In general, there can be several reasons why a subscriber may stop receiving messages:

1. If a subscriber does not ack or nack messages, the flow control limits can be reached, meaning no more messages can be delivered. This does not seem to be the case in your particular instance given that you immediately ack messages.
2. If another subscriber starts up for the same subscription, it could be receiving the messages. In this scenario, one would expect the subscriber to receive a subset of the messages rather than no messages at all.
3. Publishers just stop publishing messages and therefore there are no messages to receive. If you restart the subscriber and it starts receiving messages again, this probably isn't the case. You can also verify that a backlog is being built up by looking at the Stackdriver metric for subscription/backlog_bytes.

If your problem does not fall into one of those categories, it would be best to reach out to Google Cloud support with your project name, topic name, and subscription name so that they can narrow down the issue to either your user code, the client library itself, or the service.

回答2:

I was experiencing something similar and I was pretty sure there was not another subscriber pulling those messages.

Try this: go to the topic, create a new bogus subscription (name it whatever you want, because you'll just delete it later). Right after I did that both the fake subscription (which I was using the python sample code client to subscribe to) and the real one was receiving messages again. Strange solution, but maybe it kicked the topic awake again.

Hopefully someone from Google could give us some insight into what's happening here, but I'm definitely not paying them enough to get direct support.

回答3:

Few changes will help you to investigate the issue better: - Check error from Receive - Use separate context for Receive

ctx := context.Background()
err := sub.Receive(ctx, func(ctx context.Context, msg *pubsub.Message) {
    msg.Ack()
})
if err != nil {
    log.Fatal(err)
}

回答4:

Does your code work before? I have problems with PubSub since today. Methods like get_topic(), create_topic() in Python PubSub library stop working, but I don't have any problems with sending and pulling messages. Yesterday everything was working fine but today not...