Re: Query is over 2x slower with jit=on

From: Andres Freund <andres(at)anarazel(dot)de>
To: "Jonathan S(dot) Katz" <jkatz(at)postgresql(dot)org>
Cc: Andreas Joseph Krogh <andreas(at)visena(dot)com>, Robert Haas <robertmhaas(at)gmail(dot)com>, Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>, PostgreSQL Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org>
Subject: Re: Query is over 2x slower with jit=on
Date: 2018-08-22 23:13:01
Message-ID: 20180822231301.ybjvolekzojkme7x@alap3.anarazel.de
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On 2018-08-22 18:29:58 -0400, Jonathan S. Katz wrote:
>
> > On Aug 22, 2018, at 2:58 PM, Andreas Joseph Krogh <andreas(at)visena(dot)com> wrote:
> >
> > På onsdag 22. august 2018 kl. 20:52:05, skrev Andres Freund <andres(at)anarazel(dot)de <mailto:andres(at)anarazel(dot)de>>:
> > On 2018-08-22 19:51:12 +0200, Andreas Joseph Krogh wrote:
> > > I thought JITing of prepared queries happended once (in "prepare")
> >
> > No, it happens when the first JITed function is executed.
> >
> >
> > > so it didn't have to do the JITing every time the query is
> > > executed. Isn't the previously generated bytecode usable for
> > > subsequent queries?
> >
> > No, not currently. There's some reasons preventing that (primarily that
> > we currently rely on addresses of certain things not to change during
> > execution). There's ongoing work to change that, but that's certainly
> > not going to be ready for v11.
> >
> > Greetings,
> >
> > Andres Freund
> >
> >
> > Ok, thanks for clarifying.
>
> Per earlier note[1] I was able to reproduce this issue with similar results to
> Andreas while running 11 Beta 3.
>
> jit = on
> https://explain.depesz.com/s/vgzD <https://explain.depesz.com/s/vgzD>
>
> Planning Time: 0.921 ms
> JIT:
> Functions: 193
> Generation Time: 121.595 ms
> Inlining: false
> Inlining Time: 0.000 ms
> Optimization: false
> Optimization Time: 58.045 ms
> Emission Time: 1201.100 ms
> Execution Time: 1628.017 ms
>
> jit = off
> https://explain.depesz.com/s/AvZM <https://explain.depesz.com/s/AvZM>
>
> Planning Time: 1.398 ms
> Execution Time: 256.473 ms
>
> I increased the the search range I used in the query by 3x, and got these numbers:
>
> jit=on
> Planning Time: 0.931 ms
> JIT:
> Functions: 184
> Generation Time: 126.587 ms
> Inlining: true
> Inlining Time: 98.865 ms
> Optimization: true
> Optimization Time: 20518.982 ms
> Emission Time: 7270.963 ms
> Execution Time: 28772.576 ms
>
> jit=off
> Planning Time: 1.527 ms
> Execution Time: 959.160 ms

For the archives sake: This likely largely is the consequence of
building with LLVM's expensive assertions enabled, as confirmed by
Jonathan over IM.

Greetings,

Andres Freund

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