Re: A performance issue with Memoize

From: David Rowley <dgrowleyml(at)gmail(dot)com>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: Richard Guo <guofenglinux(at)gmail(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: A performance issue with Memoize
Date: 2024-01-26 21:02:51
Message-ID: CAApHDvpc=BgW0iSjvcQg-tf05Pd7-rcjccFzJsGiDe0srDG8Tg@mail.gmail.com
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On Sat, 27 Jan 2024 at 09:41, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>
> David Rowley <dgrowleyml(at)gmail(dot)com> writes:
> > I've adjusted the comments to what you mentioned and also leaned out
> > the pretty expensive test case to something that'll run much faster
> > and pushed the result.
>
> drongo and fairywren are consistently failing the test case added
> by this commit. I'm not quite sure why the behavior of Memoize
> would be platform-specific when we're dealing with integers,
> but ...

Maybe snprintf(buf, "%.*f", 0, 5.0 / 2.0); results in "3" on those
rather than "2"?

Looking at the code in fmtfloat(), we fallback on the built-in snprintf.

I can try changing the unique1 < 5 to unique1 < 4 to see that's more stable.

David

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