Re: Service outage: each postgres process use the exact amount of the configured work_mem

On Fri, Apr 14, 2017 at 1:12 PM, Moreno Andreo <moreno(dot)andreo(at)evolu-s(dot)it>
wrote:

> Hi all,
> About 2 hours and half ago, suddenly (and on the late afternoon of the
> Easter Friday), customers reported failing connections to our server, or
> even very slow.
> After a bit of checking (that also involved server reboot) I noticed
> (using top) that every process regarding postgres is using exactly the
> amout I configured as work_mem (3 GB). And AFAIK it's not good.
>
> 30085 postgres 20 0 *3370048* 156656 153876 S 6.7 0.3 0:00.20 postgres
> 29833 postgres 20 0 *3370000* 65260 62416 S 1.7 0.1 0:00.17 postgres
> 29632 postgres 20 0 *3372468* 11712 6028 S 0.7 0.0 0:00.60 postgres
>
> What can be happened?
> Nothing has been touched....
> postgresql 9.5.6 on debian 8 just apt-get upgrade'd
>
> Any help would be appreciated.
> Moreno.
>

*>using exactly the amout I configured as work_mem (3 GB).*

*You are right, that is bad, but that is your own fault. 3GB of work_mem is
very bad, Try lowing in to something more reasonable, like 20GB.*

*https://www.postgresql.org/docs/9.5/static/runtime-config-resource.html#RUNTIME-CONFIG-RESOURCE-MEMORY
<https://www.postgresql.org/docs/9.5/static/runtime-config-resource.html#RUNTIME-CONFIG-RESOURCE-MEMORY>"several
running sessions could be doing such operations concurrently. Therefore,
the total memory used could be many times the value of work_mem; it is
necessary to keep this fact in mind when choosing the value."*

--
*Melvin Davidson*
I reserve the right to fantasize. Whether or not you
wish to share my fantasy is entirely up to you.