fedme
How to investigate DB errors like "client timed out because it queued and checked out the connection for longer than..."
Hi,
We’re starting to collect many of these errors in our logs and I am trying to understand how we can investigate them further:
Postgrex.Protocol (#PID<0.1264.0>) disconnected: ** (DBConnection.ConnectionError) client #PID<0.1555.0> timed out because it queued and checked out the connection for longer than 15000ms
I have read this topic and I understand these are caused by slow queries.
Now I am wondering, can Postgrex/Ecto be configured to log the slow query together with the above error?
I know I can find slow queries in a different way (e.g. with Postgres’pg_stat_statements extension), but it would be extremely useful if I could get some indication of what DB operation caused the timeout detailed in the error log.
Is that error log about a DB connection pool process crashing due to a timeout? Will it cause the caller process to crash as well? Maybe there’s a way to trap the timeout and log it somehow?
Thanks for your help!
Marked As Solved
LostKobrakai
Not sure you understood my comments correctly. You can get results by looking for slow queries, but a pool timeout is not guaranteed to come from a slow query. It could just as much be from a lot of fast queries accumulating their time needed to complete – or to an extreme by not running any query at all, but just leaving the connection checked out for longer than the timeout.
The better way to diagnose this is to see if the stacktrace printed can be extended to get out of general code paths and into ones which are useful for debugging.
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pdgonzalez872
LostKobrakai
Yes and yes. But given this is a timeout for the pooled connection this means it’s not bound to a particular query. You can e.g. do Repo.checkout(fn -> Process.sleep(:infinity) end) and you’d get that error without any query involved.
c4710n
IMO, you have to diagnose this problem from the slow query.
Edit: checkout the below explaination of @LostKobrakai.
If you guess that the root cause is slow queries. You can find the slow queries by using the tools provided by PostgreSQL (which you said above). Or, you can use Ecto directly. Here’s how:
Ecto supports metrics which are reported by
:telemetry.
You can log slow queries like this - Output slow Ecto queries to logs · GitHub.(The gist is picked randomly from the Internet…
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