Re: maintenance_work_mem used by Vacuum

On Sat, Oct 12, 2019 at 8:45 PM Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
>
> On Sat, Oct 12, 2019 at 10:49 AM Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com> wrote:
> >
> > On Fri, Oct 11, 2019 at 5:13 PM Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
> > >
> > > That's right, but OTOH, if the user specifies gin_pending_list_limit
> > > as an option during Create Index with a value greater than GUC
> > > gin_pending_list_limit, then also we will face the same problem. It
> > > seems to me that we haven't thought enough on memory usage during Gin
> > > pending list cleanup and I don't want to independently make a decision
> > > to change it. So unless the original author/committer or some other
> > > people who have worked in this area share their opinion, we can leave
> > > it as it is and make a parallel vacuum patch adapt to it.
> >
> > Yeah I totally agreed.
> >
> > Apart from the GIN problem can we discuss whether need to change the
> > current memory usage policy of parallel utility command described in
> > the doc? We cannot control the memory usage in index AM after all but
> > we need to generically consider how much memory is used during
> > parallel vacuum.
> >
>
> Do you mean to say change the docs for a parallel vacuum patch in this
> regard? If so, I think we might want to do something for
> maintenance_work_mem for parallel vacuum as described in one of the
> emails above [1] and then change the docs accordingly.
>

Yes agreed. I thought that we can discuss that while waiting for other
opinion on the memory usage of gin index's pending list cleanup. For
example one of your suggestions[1] is simple and maybe acceptable but
I guess that it can deal with only gin indexes but not other index AMs
that might consume more memory.

[1] https://www.postgresql.org/message-id/CAA4eK1JhpNsTiHj%2BJOy3N8uCGyTBMH8xDhUEtBw8ZeCAPRGp6Q%40mail.gmail.com

Regards,

--
Masahiko Sawada