Re: Memory consumed by child SpecialJoinInfo in partitionwise join planning

Hi Ashutosh,

On Mon, Feb 19, 2024 at 10:01 PM Ashutosh Bapat
<ashutosh(dot)bapat(dot)oss(at)gmail(dot)com> wrote:
> On Sun, Feb 18, 2024 at 10:55 PM Tomas Vondra
> <tomas(dot)vondra(at)enterprisedb(dot)com> wrote:
> >
> > Hi,
> >
> > I took a quick look at this patch today. I certainly agree with the
> > intent to reduce the amount of memory during planning, assuming it's not
> > overly disruptive. And I think this patch is fairly localized and looks
> > sensible.
>
> Thanks for looking at the patch-set.
> >
> > That being said I'm a big fan of using a local variable on stack and
> > filling it. I'd probably go with the usual palloc/pfree, because that
> > makes it much easier to use - the callers would not be responsible for
> > allocating the SpecialJoinInfo struct. Sure, it's a little bit of
> > overhead, but with the AllocSet caching I doubt it's measurable.
>
> You are suggesting that instead of declaring a local variable of type
> SpecialJoinInfo, build_child_join_sjinfo() should palloc() and return
> SpecialJoinInfo which will be freed by free_child_sjinfo()
> (free_child_sjinfo_members in the patch). I am fine with that.

Agree with Tomas about using makeNode() / pfree(). Having the pfree()
kind of makes it extra-evident that those SpecialJoinInfos are
transitory.

> > I did put this through check-world on amd64/arm64, with valgrind,
> > without any issue. I also tried the scripts shared by Ashutosh in his
> > initial message (with some minor fixes, adding MEMORY to explain etc).
> >
> > The results with the 20240130 patches are like this:
> >
> > tables master patched
> > -----------------------------
> > 2 40.8 39.9
> > 3 151.7 142.6
> > 4 464.0 418.5
> > 5 1663.9 1419.5

Could you please post the numbers with the palloc() / pfree() version?

--
Thanks, Amit Langote