Due to various circumstances I've got a topic that has hit its max size of 5 GB. Now what I'm seeing is that when an app tries to publish to the topic it gets an exception. That's all good and corresponds to the documentation. But what's odd is that when I'm processing the subscriptions, messages are added just as fast as I can receive them.
I know that I'm receiving at a way higher pace than what my apps are publishing to the topic, so it seems that some part of the infrastructure is adding the messages. The apps are normally publishing perhaps 2-3 messages per second, but when I wrote a script that quickly drained the deadletter queue to clear up space, messages were added to the subscription very fast - thousands of messages almost instantly.
Is there some internal retry logic that buffers messages and attempts to publish them as size becomes available? Or is there another explanation for why I'm seeing messages being added to the topic's subscriptions that are not directly published by my own apps?