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

Debian 8:
Linux <hostname> 3.16.0-4-amd64 #1 SMP Debian 3.16.43-2+deb8u1 (2017-06-18)
x86_64 GNU/Linux

On 23 June 2017 at 18:57, Andres Freund <andres(at)anarazel(dot)de> wrote:

> Hi,
>
> On 2017-06-19 14:49:07 +0000, josef(dot)machytka(at)gmail(dot)com wrote:
> > 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..."
>
> Which version of the os & kernel is this? This kind of sounds like the
> symptoms that we've observed more frequently a while ago with
> the kernel's transparent_hugepages management.
>
> Greetings,
>
> Andres Freund
>