Horton

Re: A qsort template

David Rowley <dgrowleyml@gmail.com>

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From: David Rowley <dgrowleyml@gmail.com>
To: John Naylor <john.naylor@enterprisedb.com>
Cc: Thomas Munro <thomas.munro@gmail.com>, Andres Freund <andres@anarazel.de>, Justin Pryzby <pryzby@telsasoft.com>, Peter Geoghegan <pg@bowt.ie>, pgsql-hackers <pgsql-hackers@postgresql.org>, Robert Haas <rhaas@postgresql.org>
Date: 2022-04-22T04:13:08Z
Lists: pgsql-hackers 
On Thu, 21 Apr 2022 at 19:09, John Naylor <john.naylor@enterprisedb.com> wrote:
> I intend to commit David's v2 fix next week, unless there are
> objections, or unless he beats me to it.

I wasn't sure if you wanted to handle it or not, but I don't mind
doing it, so I just pushed it after a small adjustment to a comment.

Before going ahead with it I did test a 2-key sort where the leading
key values were all the same.  I wondered if we'd still see any
regression from having to re-compare the leading key all over again.

I just did:

create table ab (a bigint, b bigint);
insert into ab select 0,x from generate_series(1,1000000)x;
vacuum freeze ab;

I then ran:
select * from ab order by a,b offset 1000000;

697492434 (Specialize tuplesort routines for different kinds of
abbreviated keys)
$ pgbench -n -f bench1.sql -T 60 -M prepared postgres
tps = 10.651740 (without initial connection time)
tps = 10.813647 (without initial connection time)
tps = 10.648960 (without initial connection time)

697492434~1 (Remove obsolete comment)
$ pgbench -n -f bench1.sql -T 60 -M prepared postgres
tps = 9.957163 (without initial connection time)
tps = 10.191168 (without initial connection time)
tps = 10.145281 (without initial connection time)

So it seems there was no regression for that case, at least, not on
the AMD machine that I tested on.

David

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.