Horton

Re: Parallel Aggregates for string_agg and array_agg

Andres Freund <andres@anarazel.de>

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From: Andres Freund <andres@anarazel.de>
To: Mark Dilger <hornschnorter@gmail.com>
Cc: Tom Lane <tgl@sss.pgh.pa.us>, David Rowley <david.rowley@2ndquadrant.com>, Alvaro Herrera <alvherre@alvh.no-ip.org>, Stephen Frost <sfrost@snowman.net>, Tomas Vondra <tomas.vondra@2ndquadrant.com>, PostgreSQL-development <pgsql-hackers@postgresql.org>
Date: 2018-05-01T21:11:47Z
Lists: pgsql-hackers 
Hi,

On 2018-05-01 14:09:39 -0700, Mark Dilger wrote:
> I don't care which order the data is in, as long as x[i] and y[i] are
> matched correctly.  It sounds like this patch would force me to write
> that as, for example:
> 
> select array_agg(a order by a, b) AS x, array_agg(b order by a, b) AS y
>   from generate_a_b_func(foo);
> 
> which I did not need to do before.

Why would it require that? Rows are still processed row-by-row even if
there's parallelism, no?

Greetings,

Andres Freund

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.