Shutdown idle aggregate processes

[commanded]

Shutdown idle aggregate processes

[henry-hz]

maybe add a mechanism to generate an event before shutdown, so sagas will be able to reverse any long transaction ?

[Papipo]

It doesn't make sense that aggregates emit events because they haven't been receiving commands lately.

[henry-hz]

yep, agree. there are two reasons to shutdown, or the business process was finished, or we need more memory, and that aggregate has been sparsely used. for the first, the PM could shutdown them sending stop commands, but for the former, the solution above is fine. an algorithm could calculate the desired "cache" memory, and sets the best timeout based on memory needs

[Papipo]

I guess that this is one of those cases that depends on the use case. Providing configurable timeouts would probably suffice. It's just a matter of finding a good value for your application.

[bbhoss]

Hibernating after a timeout could also be a good idea, since it will reduce memory to be as small as possible. You could probably have a timeout handler that registers (probably in ETS/Registry) the process somewhere as "in hibernation", with the current time, then have some sort of reaper that decides when to kill/shutdown processes. This is a common issue in actor languages, and why Pony was built to allow garbage collecting the actors themselves, which seems like a pretty rare/one of a kind ability.

[slashdotdash]

@bbhoss GenServer already has support for handling timeouts. You can return a timeout (in milliseconds) as part of the reply to handle_cast and handle_call requests. If there are no subsequent requests within the given timeout period, the GenServer will receive a :timeout message and can be stopped.

It just needs to be implemented for the aggregate GenServer.

[bbhoss]

I understand that, what I'm proposing is in the timeout message handler, we register as hibernated, then return a :hibernate tuple. Then a configurable reaper could evict the processes later.

[slashdotdash]

Done in #57.

[slashdotdash]

Published to Hex as v0.11.0