Re: SQLFunctionCache and generic plans

čt 27. 2. 2025 v 20:52 odesílatel Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> napsal:

> Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com> writes:
> > čt 27. 2. 2025 v 13:25 odesílatel Alexander Pyhalov <
> > a(dot)pyhalov(at)postgrespro(dot)ru> napsal:
> >>> Unfortunately, there is about 5% slowdown for inlined code, and for
> >>> just plpgsql code too.
>
> >> Hi. I've tried to reproduce slowdown and couldn't.
>
> > I'll try to get profiles.
>
> I tried to reproduce this too. What I got on my usual development
> workstation (RHEL8/gcc 8.5.0 on x86_64) was:
>
> fx2 example: v6 patch about 2.4% slower than HEAD
> fx4 example: v6 patch about 7.3% slower than HEAD
>
> I was quite concerned after that result, but then I tried it on
> another machine (macOS/clang 16.0.0 on Apple M1) and got:
>
> fx2 example: v6 patch about 0.2% slower than HEAD
> fx4 example: v6 patch about 0.7% faster than HEAD
>
> (These are average-of-three-runs tests on --disable-cassert
> builds; I trust you guys were not doing performance tests on
> assert-enabled builds?)
>
> So taken together, our results are all over the map, anywhere
> from 7% speedup to 7% slowdown. My usual rule of thumb is that
>

Where do you see 7% speedup? Few lines up you wrote 0.7% faster.

you can see up to 2% variation in this kind of microbenchmark even
> when "nothing has changed", just due to random build details like
> whether critical loops cross a cacheline or not. 7% is pretty
> well above that threshold, but maybe it's just random build
> variation anyway.
>
> Furthermore, since neither example involves functions.c at all
> (fx2 would be inlined, and fx4 isn't SQL-language), it's hard
> to see how the patch would directly affect either example unless
> it were adding overhead to plancache.c. And I don't see any
> changes there that would amount to meaningful overhead for the
> existing use-case with a raw parse tree.
>
> So right at the moment I'm inclined to write this off as
> measurement noise. Perhaps it'd be worth checking a few
> more platforms, though.
>
> regards, tom lane
>