Horton

Re: Add proper planner support for ORDER BY / DISTINCT aggregates

Tom Lane <tgl@sss.pgh.pa.us>

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From: Tom Lane <tgl@sss.pgh.pa.us>
To: David Rowley <dgrowleyml@gmail.com>
Cc: Richard Guo <guofenglinux@gmail.com>, Dean Rasheed <dean.a.rasheed@gmail.com>, Ronan Dunklau <ronan.dunklau@aiven.io>, Justin Pryzby <pryzby@telsasoft.com>, Pavel Luzanov <p.luzanov@postgrespro.ru>, pgsql-hackers@lists.postgresql.org, Ranier Vilela <ranier.vf@gmail.com>
Date: 2023-01-11T04:32:04Z
Lists: pgsql-hackers 
David Rowley <dgrowleyml@gmail.com> writes:
> I think whatever the fix is here, we should likely ensure that the
> results are consistent regardless of which Aggrefs are the presorted
> ones.  Perhaps the easiest way to do that, and to ensure we call the
> volatile functions are called the same number of times would just be
> to never choose Aggrefs with volatile functions when doing
> make_pathkeys_for_groupagg().

There's existing logic in equivclass.c and other places that tries
to draw very tight lines around what we'll assume about volatile
sort expressions (pathkeys).  It sounds like there's someplace in
this recent patch that didn't get that memo.

			regards, tom lane

Commits

  1. Don't presort ORDER BY/DISTINCT Aggrefs with volatile functions

  2. Add enable_presorted_aggregate GUC

  3. Remove pessimistic cost penalization from Incremental Sort

  4. Fix hypothetical problem passing the wrong GROUP BY pathkeys

  5. Remove unused fields from ExprEvalStep

  6. Improve performance of ORDER BY / DISTINCT aggregates

  7. Refactor function parse_subscription_options.