Re: Let's make PostgreSQL multi-threaded

Greetings,

* David Geier (geidav(dot)pg(at)gmail(dot)com) wrote:
> On 8/11/23 14:05, Merlin Moncure wrote:
> > Hm, noted this upthread, but asking again, does this
> > help/benefit interactions with the operating system make oom kill
> > situations less likely?   These things are the bane of my existence, and
> > I'm having a hard time finding a solution that prevents them other than
> > running pgbouncer and lowering max_connections, which adds complexity. 
> > I suspect I'm not the only one dealing with this.   What's really scary
> > about these situations is they come without warning.  Here's a pretty
> > typical example per sar -r.
> >
> > The conjecture here is that lots of idle connections make the server
> > appear to have less memory available than it looks, and sudden transient
> > demands can cause it to destabilize.
>
> It does in the sense that your server will have more memory available in
> case you have many long living connections around. Every connection has less
> kernel memory overhead if you will. Of course even then a runaway query will
> be able to invoke the OOM killer. The unfortunate thing with the OOM killer
> is that, in my experience, it often kills the checkpointer. That's because
> the checkpointer will touch all of shared buffers over time which makes it
> likely to get selected by the OOM killer. Have you tried disabling memory
> overcommit?

This is getting a bit far afield in terms of this specific thread, but
there's an ongoing effort to give PG administrators knobs to be able to
control how much actual memory is used rather than depending on the
kernel to actually tell us when we're "out" of memory. There'll be new
patches for the September commitfest posted soon. If you're interested
in this issue, it'd be great to get more folks involved in review and
testing.

Thanks!

Stephen