Presence list keep growing when using Presence.update

[arjan]

It seems #172 (released in 2.1.2) seems to have introduced a bug where the list of presences keeps growing when a process uses Presence.update.

How to reproduce

The following gist is a test script that starts a PubSub server and a Phoenix presence tracker.

https://gist.github.com/arjan/6702b4b9fd6b97e9b1a355313ed1620b

Periodically, genserver processes are started that do Presence.track and, a bit later, Presence.update, and another bit later stop again.

A poller process runs that shows the number of running (local) processes, the number of items in the presence list, and the number of items in the presence list split out by node.

Run the test script in 2 terminals with:

▶ elixir --name a@127.0.0.1 --cookie hello ./presence_bug.exs
▶ elixir --name b@127.0.0.1 --cookie hello ./presence_bug.exs

When running on 2.1.1, the presence count is stable, settling at about ~100 processes per node.

10:30:43.465 [warning] Local processes: 106 - Presence count: 178 - Per node counts: ["a@127.0.0.1": 106, "b@127.0.0.1": 110]

When running on 2.1.2, the presence count keeps increasing, because the presences for the non-local nodes are not cleaned up, the per-node counts for the non-local node keeps increasing, eg:

10:29:55.630 [warning] Local processes: 100 - Presence count: 355 - Per node counts: ["a@127.0.0.1": 322, "b@127.0.0.1": 100]

[MattiasOlla]

Thanks for reporting, we also had issues with this. It also led to our application consuming more than twice as much more memory as before updating:

[jonatanklosko]

@arjan thanks for the great reproduction! I'm looking into this.

[chrismccord]

Fixed in 2.1.3