Re: BUG #17255: Server crashes in index_delete_sort_cmp() due to race condition with vacuum

Hi,

On 2022-03-10 19:40:21 -0800, Peter Geoghegan wrote:
> On Thu, Mar 10, 2022 at 7:13 PM Andres Freund <andres@anarazel.de> wrote:
> > > On Wed, Mar 9, 2022 at 4:25 PM Andres Freund <andres@anarazel.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