Re: BUG #14714: long running sessions from remote instance seems to hang some times

2017-06-19 16:49 GMT+02:00 <josef(dot)machytka(at)gmail(dot)com>:

> The following bug has been logged on the website:
>
> Bug reference: 14714
> Logged by: Josef Machytka
> Email address: josef(dot)machytka(at)gmail(dot)com
> PostgreSQL version: 9.6.3
> Operating system: Debian jessie
> Description:
>
> On pg 9.6.* we have sometimes strange problem with some sessions. We
> experienced it from bash scripts, golang program and node.js applications.
> Environment are Google Compute Engine instances with Debian 8.
>
> Sometimes some session goes into some kind of "drowsy" state and runs
> incredibly slowly. It causes some very low disk IO and runs like 20x slower
> then usual. This happens mainly when database is under heavy load and it
> happens randomly to different tasks. It happens randomly to both
> connections
> from local instance (cronjob running on instance with PG) and remote
> connections from other instances.
>
> When we restart task it runs normally. I cannot see any changes in process
> priority in OS, process switches between sleeping and running state and I
> do
> not see any locks or waits in pg_stat_activity or pg_locks. Usually all
> other processes finish OK and this "drowsy" one runs "for ever..."
>
> We implemented timeouts for PG tasks into our programs to restart tasks but
> it very annoying and we have to use long enough timeouts anyway so it
> delays
> tasks.... It happens from time to time also to dblink connections inside pg
> function so we had to rewrite our programs which were running without any
> problems on PG 9.5. Problems started when we switched to PG 9.6 and we
> experienced them on all minor versions - we currently run 9.6.3 and problem
> is still present...
>
> Do you please have any advice what to check or what setting might help?
>

it can be spin lock issue. Try to use "perf top". Install postgresql-server
debug symbols before.

what is your share buffers configuration?

Regards

Pavel

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