From: | Andres Freund <andres(at)anarazel(dot)de> |
---|---|
To: | Peter Geoghegan <pg(at)bowt(dot)ie> |
Cc: | Dmitry Dolgov <9erthalion6(at)gmail(dot)com>, Alexander Lakhin <exclusion(at)gmail(dot)com>, Matthias van de Meent <boekewurm+postgres(at)gmail(dot)com>, PostgreSQL mailing lists <pgsql-bugs(at)lists(dot)postgresql(dot)org> |
Subject: | Re: BUG #17255: Server crashes in index_delete_sort_cmp() due to race condition with vacuum |
Date: | 2022-03-11 03:46:32 |
Message-ID: | 20220311034632.pszcrrhnhtd4myll@alap3.anarazel.de |
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Lists: | pgsql-bugs |
Hi,
On 2022-03-10 19:40:21 -0800, Peter Geoghegan wrote:
> On Thu, Mar 10, 2022 at 7:13 PM Andres Freund <andres(at)anarazel(dot)de> wrote:
> > > On Wed, Mar 9, 2022 at 4:25 PM Andres Freund <andres(at)anarazel(dot)de> wrote:
> > > > I think it'd be nicer if we did the horizon determination after allocating
> > > > space for dead tuples... But it's still better than today, so...
> > >
> > > Why would it be nicer?
> >
> > Large allocation can take a bit. Especially dead_item_alloc() sneakily
> > initializes parallelism (which is darn ugly). Determining the horizon after
> > doing expensive stuff gives you a slightly better horizon...
>
> I'm confused. You recently said "I don't think the minor optimization
> [delaying establishing vistest] does anything (which I had stated
> wrongly at some point in this thread)". But you now seem to be saying
> that delaying establishing vistest has at least some small value as an
> optimization. At least in theory.
I'm not talking about just moving the vistest acquisition, but also
vacuum_set_xid_limits(). Which obviously *does* benefit from delaying as long
as possible.
> > The whole s/nblocks/rel_pages/ seems like it should be done separately.
>
> I'll break the mechanical s/nblocks/rel_pages/ out into a dedicated
> commit, then.
Cool.
Greetings,
Andres Freund
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