Re: Crash in BRIN minmax-multi indexes

On Mon, Oct 03, 2022 at 07:53:34PM +0200, Tomas Vondra wrote:
> On 9/29/22 08:53, Jaime Casanova wrote:
> > ...
> >
> > Just found one more ocurrance of this one with this index while an
> > autovacuum was running:
> >
> > """
> > CREATE INDEX bt_f8_heap_seqno_idx
> > ON public.bt_f8_heap
> > USING brin (seqno float8_minmax_multi_ops);
> > """
> > Attached is a backtrace.
>
> Thanks for the report!
>
> I think I see the issue - brin_minmax_multi_union does not realize the
> two summaries could have just one range each, and those can overlap so
> that merge_overlapping_ranges combines them into a single one.
>
> This is harmless, except that the assert int build_distances is overly
> strict. Not sure if we should just remove the assert or only compute the
> distances with (neranges>1).
>
> Do you happen to have the core dump? It'd be useful to look at ranges_a
> and ranges_b, to confirm this is indeed what's happening.
>

I do have it.

(gdb) p *ranges_a
$4 = {
typid = 701,
colloid = 0,
attno = 0,
cmp = 0x0,
nranges = 0,
nsorted = 1,
nvalues = 1,
maxvalues = 32,
target_maxvalues = 32,
values = 0x55d2ea1987c8
}
(gdb) p *ranges_b
$5 = {
typid = 701,
colloid = 0,
attno = 0,
cmp = 0x0,
nranges = 0,
nsorted = 1,
nvalues = 1,
maxvalues = 32,
target_maxvalues = 32,
values = 0x55d2ea196da8
}

--
Jaime Casanova
Director de Servicios Profesionales
SystemGuards - Consultores de PostgreSQL