Google pubsub golang订户闲置了几个小时后停止接收新发布的消息

Question

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?

Answer 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.