Re: BUG #17793: Query with large number of joins crashes PostgreSQL

On 2/14/23 09:47, Tom Lane wrote:
> Francisco Olarte <folarte(at)peoplecall(dot)com> writes:
>> On Tue, 14 Feb 2023 at 11:29, PG Bug reporting form
>> <noreply(at)postgresql(dot)org> wrote:
>>> It looks like the OS is killing the process due to running OOM, which is not
>>> very surprising when looking at the query. Is this expected, or should PG
>>> have guards in place to prevent this from happening?
>
>> When you run postgres in an environment where someone ( OOM killer )
>> can K9 it, protection is hard. IIRC OOM can kill you because ANOTHER
>> process touches memory, among other things.
>
> Yeah. We have no visibility into what the OOM killer will choose to
> allow or not allow at any instant.
>
>> ( I do run DBs in machines w/ overcommit disabled, this prevents it
>> from happening, but it is not Pg who prevents it ).
>
> If overcommit-disabled doesn't seem practical, another idea that's
> been recommended is to start the postmaster under a "ulimit -v"
> setting chosen to cause plain ENOMEM failures before the OOM
> killer kicks in.

Given:
> It looks like the OS is killing the process due to running OOM ...
> I could reproduce it using a fresh docker container of the image
> "postgres:13.10".

I gather the OP is running Postgres in a container. If so, and if they
have a memory.limit set (also assuming cgroup v1, otherwise memory.max
for cgroup v2), disabling overcommit at the host level will not prevent
an OOM kill when the cgroup exceeds memory.limit

--
Joe Conway
PostgreSQL Contributors Team
RDS Open Source Databases
Amazon Web Services: https://aws.amazon.com