ReliableTopic only deletes expired subscribers when a message is read

[faroukfaiz10]

Observation

ReliableTopics only remove expired subscribers and trim messages (i.e. those read by all subscribers) when a new message is published on the topic (i.e. when the blocking XREAD succeeds to read a message).

Problematic

This is problematic for Reliable topics that are not very active (i.e. do not have a lot of messages published), but have a lot of new subscribers. Over time, the subscribers list grows very large (of expired subscribers) because they’re only removed on new message reception, which doesn’t happen very often.

As a result, when a message gets published, it doesn't get deleted for a long time (months in my case), because a lot of the expired subscribers, that will never read that message, were not removed from the list.

Questions

1. Why does the deletion of old subscribers (and the trimming of messages as a result) not happen in every poll (i.e. even if no message was read)? That way, ReliableTopics that do not get a lot of published messages will behave like those that get a lot of published messages => Both will not have expired subscribers left for long.

2. Suppose I want expired subscribers to be deleted ASAP. Is there an easier way to achieve this than to manually do it myself (e.g. on a separate cron job)?

[mrniko]

I found the cause. All expired subscribers weren't deleted at once per call, only a single one.

Below is the change

69b7110

[faroukfaiz10]

Great! Thanks for your reactivity on this.