Horton

Re: Parallel Aggregates for string_agg and array_agg

Tomas Vondra <tomas.vondra@2ndquadrant.com>

View thread View on postgr.es
From: Tomas Vondra <tomas.vondra@2ndquadrant.com>
To: David Rowley <david.rowley@2ndquadrant.com>
Cc: Tom Lane <tgl@sss.pgh.pa.us>, Stephen Frost <sfrost@snowman.net>, Andres Freund <andres@anarazel.de>, PostgreSQL-development <pgsql-hackers@postgresql.org>
Date: 2018-03-29T13:00:34Z
Lists: pgsql-hackers 

On 03/29/2018 05:49 AM, David Rowley wrote:
> On 29 March 2018 at 03:05, Tomas Vondra <tomas.vondra@2ndquadrant.com> wrote:
>> On 03/28/2018 03:54 PM, Tom Lane wrote:
>>> I had in mind to look at exprType() of the argument.
>>
>> Right, I'm fine with that.
> 
> Attached is v9, which is based on Tom's v8 but includes the new tests
> and I think the required fix to disable use of the serial/deserial
> function for array_agg().
> 

I have only looked at the diff, but it seems fine to me (in the sense
that it's doing the right checks to disable parallelism only when really
needed).

FWIW I wonder if we might simply fallback to input/output functions when
the send/receive functions are not available. Not sure it's worth it.

regards

-- 
Tomas Vondra                  http://www.2ndQuadrant.com
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services

Commits

  1. Fix unstable aggregate regression test

  2. Allow parallel aggregate on string_agg and array_agg

  3. Improve performance of ORDER BY / DISTINCT aggregates

  4. Support ORDER BY within aggregate function calls, at long last providing a

  5. Fix broken markup.