Horton

Re: A qsort template

Thomas Munro <thomas.munro@gmail.com>

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From: Thomas Munro <thomas.munro@gmail.com>
To: Andres Freund <andres@anarazel.de>
Cc: Justin Pryzby <pryzby@telsasoft.com>, John Naylor <john.naylor@enterprisedb.com>, Peter Geoghegan <pg@bowt.ie>, pgsql-hackers <pgsql-hackers@postgresql.org>, Robert Haas <rhaas@postgresql.org>
Date: 2022-04-03T05:46:28Z
Lists: pgsql-hackers

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On Sun, Apr 3, 2022 at 11:11 AM Andres Freund <andres@anarazel.de> wrote:
> On 2022-04-03 09:45:13 +1200, Thomas Munro wrote:
> > I think we just need to decide up front if we're in a situation that
> > can't provide datum1/isnull1 (in this case because it's an expression
> > index), and skip the optimised paths.  Here's an experimental patch...
> > still looking into whether there are more cases like this...

I didn't find anything else.

Maybe it'd be better if we explicitly declared whether datum1 is used
in each tuplesort mode's 'begin' function, right next to the code that
installs the set of routines that are in control of that?  Trying that
in this version.  Is it clearer what's going on like this?

> That's a lot of redundant checks. How about putting all the checks for
> optimized paths into one if (state->sortKeys && !state->disabl1e_datum1)?

OK, sure.

> I'm a bit worried that none of the !ubsan tests failed on this...

In accordance with whoever-it-was-that-said-that's law about things
that aren't tested, this are turned out to be broken already[1].  Once
we fix that we should have a new test in the three that might also
eventually have failed under this UB, given enough chaos.

[1] https://www.postgresql.org/message-id/CA%2BhUKG%2BbA%2BbmwD36_oDxAoLrCwZjVtST2fqe%3Db4%3DqZcmU7u89A%40mail.gmail.com

Commits

  1. Remove debug messages from tuplesort_sort_memtuples()

  2. Fix performance regression in tuplesort specializations

  3. Fix tuplesort optimization for CLUSTER-on-expression.

  4. Initial pgindent and pgperltidy run for v14.

  5. Specialize checkpointer sort functions.

  6. Use sort_template.h for qsort() and qsort_arg().

  7. Use sort_template.h for qsort_tuple() and qsort_ssup().

  8. Add sort_template.h for making sort functions.

  9. Use abbreviated keys for faster sorting of text datums.