Subject: Re: Parallel Aggregates for string_agg and array_agg
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>
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From: Tomas Vondra <tomas.vondra@2ndquadrant.com>
Message-ID: <13e3fd13-8152-72be-4e3c-8095e6ec0995@2ndquadrant.com>
Date: Thu, 29 Mar 2018 15:00:34 +0200
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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