manukall
Since a few days ago I keep getting the following error on my dev machine when making requests to a phoenix app:
exited in: :gen_server.call(#PID<0.656.0>, {:checkout, #Reference<0.1406881335.1305214977.237415>, true, 15000}, 5000) ** (EXIT) time out
It seems like the app works for some time and then the error happens for every request. Sometimes restarting Postgres or the app fixes the problem again for some time, but sometimes not. I suspect it maybe just works again after something times out.
I’m not sure what changed since I’ve last worked on this project some weeks ago. I’ve tried downgrading Postgresql and Elixir and also completely removed Postgresql, including the data directory.
The Phoenix logs for the affected requests show several successful queries before the error happens. It feels like connections are not checked in to the pool again, but I’ve no idea if that’s really true or where to start debugging. The same app works on a different laptop without those issues, though.
I’m on Arch Linux with Postgres 10.4, Ecto 2.2.10 and postgres 0.13.5.
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hubertlepicki
it’s difficult to answer but what is happening IMHO is that Ecto can’t check out a connection from the pool for some reason as all connections are being used.
It is possible that your app is doing something in background, or you are (even in dev) making so many parallel requests, or doing some long-running operations that they are not getting freed in time for other requests to pick up.
Can you tell me what’s your pool size config option is in dev mode, and also try to possibly bump it up to something like 30 and see if that sorts things out?
manukall
That’s what I thought, too. I’ve tried increasing pool_size and pool_overflow to 50, though and it didn’t help.
Also, from the logs it looks like maybe 6 or 7 queries are made before the timeout, so it shouldn’t be enough to exhaust the pool.
The only thing I know I’ve done since it worked was running some system upgrades. I’ve downgraded postgres again though.
manukall
Update: Seems to only happen with Erlang 20.3. After downgrading to 20.2.2, everything works again. My other project on the same machine was using 20.2.2. When I upgrade Erlang there to 20.3 it’s broken, too.
I’d like to raise this as a bug somewhere, but I’ve no idea where. I don’t know if it’s an issue with Erlang, Ecto, Postgrex, Poolboy, …
dom
That timeout would be on DBConnection. There’s a comment on a similar issue here:
https://github.com/elixir-ecto/db_connection/issues/107#issuecomment-347601857
I would also suggest
rm -rf _buildthen recompiling, just to be sure there’s no weirdness.hubertlepicki
Oh that’s interesting. I am not using 20.3 yet but it seems like a good opportunity to update one of the projects and see if I can replicate your problem. I have got one that’s matching Ecto and postgrex versions to your set up, and is reasonably big so it will be a good test.
It might be a bug in poolboy or database_connection on this specific version of Erlang.
hubertlepicki
Just to give you an update, so far in development I saw no such issues :(. We are going to deploy to staging an update some time today and we’ll see if it’ll be caught there. It’s weird.
manukall
thanks. it’s very weird. we’re only seeing the issue on my machine running arch linux. on a macbook and our ubuntu servers everything is fine. maybe it only happens with very recent postgres versions.
hubertlepicki
Damn, I migrated from Arch to Ubuntu last year :(.
manukall
good for you in this case
hubertlepicki
Well I had issues setting up Docker projects and just got fed up with constantly fighting with Arch and I’m already 33 so you know, too old to fight against my dev machine like that all the time.