Re: O(n) tasks cause lengthy startups and checkpoints

On Mon, Dec 13, 2021 at 08:53:37AM -0500, Robert Haas wrote:
> On Fri, Dec 10, 2021 at 2:03 PM Bossart, Nathan <bossartn(at)amazon(dot)com> wrote:
> > Well, I haven't had a chance to look at your patch, and my patch set
> > still only has handling for CheckPointSnapBuild() and
> > RemovePgTempFiles(), but I thought I'd share what I have anyway. I
> > split it into 5 patches:
> >
> > 0001 - Adds a new "custodian" auxiliary process that does nothing.
...
>
> I don't know whether this kind of idea is good or not.
...
>
> Another issue is that we don't want to increase the number of
> processes without bound. Processes use memory and CPU resources and if
> we run too many of them it becomes a burden on the system. Low-end
> systems may not have too many resources in total, and high-end systems
> can struggle to fit demanding workloads within the resources that they
> have. Maybe it would be cheaper to do more things at once if we were
> using threads rather than processes, but that day still seems fairly
> far off.

Maybe that's an argument that this should be a dynamic background worker
instead of an auxilliary process. Then maybe it would be controlled by
max_parallel_maintenance_workers (or something similar). The checkpointer
would need to do these tasks itself if parallel workers were disabled or
couldn't be launched.

--
Justin