Re: WIP: Faster Expression Processing v4

From: Andres Freund <andres(at)anarazel(dot)de>
To: Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com>
Cc: pgsql-hackers(at)postgresql(dot)org
Subject: Re: WIP: Faster Expression Processing v4
Date: 2017-03-13 08:03:51
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On 2017-03-12 05:40:51 +0100, Tomas Vondra wrote:
> I wanted to do a bit of testing and benchmarking on this, but 0004 seems to
> be a bit broken.

Well, "broken" in the sense that it's already outdated, because other
stuff that got merged.

> The patch does not apply anymore - there are some conflicts
> in execQual.c, but I think I fixed those. But then I ran into a bunch of
> compile-time errors, because some of the executor nodes still reference bits
> that were moved elsewhere.

Updated patch attached. Note that this patch has two changes I've not
yet evaluated performance-wise.

- New code calls UpdateDomainConstraintRef at the beginning of
expression evaluation, not for each row. That allows to generate
"proper programs" for constraint checking, which is quite useful for
performance. But it's a behaviour change.
- I have *not* changed that, but I'm less than convinced of the pattern
of "runtime" get_cached_rowtype calls.

- comments
- fix minor bug in BooleanTest brought to ligth thanks to the new
regression tests (No, IS TRUE isn't the same IS NOT FALSE)
- fix (theoretical?) issue with get_cached_rowtype() being called once
for deforming and once for forming a tuple for FieldStores.
- fixed/implemented an optimization XXX around bool AND/OR because the
solution actually makes the code easier.

What's basically missing here is:
- pgindent run and minimizing resulting damage
- A higher level explanation of how the interpreted expression
evaluation works. This patch implements "fairly standard" approach,
but it's imo sufficiently
- There's one remaining FIXME that needs to be fixed.
- I sometimes see a minor performance regression (~1.2%) in tpch-h's Q17
that might or might not be code layout related.
- continue pass to ensure all worthwhile comments from execQual.c are

Could be delayed:
- add regression tests for track_functions - I've manually verified it
works, and we previously didn't have tests either.


Andres Freund

Attachment Content-Type Size
0001-Add-expression-dependencies-on-composite-type-whole-.patch text/x-patch 18.9 KB
0002-Make-get_last_attnums-more-generic.patch text/x-patch 4.1 KB
0003-Add-autoconf-test-for-computed-goto-support.patch text/x-patch 4.0 KB
0004-WIP-Faster-expression-evaluation-and-targetlist-proj.patch text/x-patch 425.5 KB

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