Re: A qsort template

From: Daniel Gustafsson <daniel(at)yesql(dot)se>
To: Thomas Munro <thomas(dot)munro(at)gmail(dot)com>
Cc: pgsql-hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: A qsort template
Date: 2021-03-02 21:25:39
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> On 18 Feb 2021, at 04:09, Thomas Munro <thomas(dot)munro(at)gmail(dot)com> wrote:

> In another thread[1], I proposed $SUBJECT, but then we found a better
> solution to that thread's specific problem. The general idea is still
> good though: it's possible to (1) replace several existing copies of
> our qsort algorithm with one, and (2) make new specialised versions a
> bit more easily than the existing Perl generator allows. So, I'm back
> with a rebased stack of patches. I'll leave specific cases for new
> worthwhile specialisations for separate proposals; I've heard about
> several.

Just to play around with this while reviewing I made a qsort_strcmp, like in
the attached, and tested it using a ~9M word [0] randomly shuffled wordlist.
While being too small input to make any meaningful difference in runtime (it
shaved a hair off but it might well be within the error margin) there was no
regression either. More importantly, it was really simple and quick to make a
tailored qsort which is the intention with the patch. While still being a bit
of magic, moving from the Perl generator makes this slightly less magic IMO so
+1 on this approach.

A tiny nitpick on the patch itself:

+ * - ST_COMPARE(a, b) - a simple comparison expression
+ * - ST_COMPARE(a, b, arg) - variant that takes an extra argument

All tests pass and the documentation in the the sort_template.h is enough to go
on, but I would prefer to see a comment in port/qsort.c referring back to
sort_template.h for documentation.

Daniel Gustafsson

[0] shuffled 20 times over

Attachment Content-Type Size
qsort_tmpl_strcmp-patch application/octet-stream 2.9 KB

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