Re: Parallel Aggregation support for aggregate functions that use transitions not implemented for array_agg

On 2017-06-06 12:23:49 -0700, David Fetter wrote:
> On Tue, Jun 06, 2017 at 01:52:45PM -0400, Regina Obe wrote:
> > It seems CREATE AGGREGATE was expanded in 9.6 to support parallelization of
> > aggregate functions using transitions, with the addition of serialfunc and
> > deserialfunc to the aggregate definitions.
> >
> > https://www.postgresql.org/docs/10/static/sql-createaggregate.html
> >
> > I was looking at the PostgreSQL 10 source code for some example usages of
> > this and was hoping that array_agg and string_agg would support the feature.
> > At a cursory glance, it seems they do not use this.
> > Examples I see that do support it are the average and standard deviation
> > functions.
> >
> > Is there a reason for this or it just wasn't gotten to?

I'd suggest trying to write a parallel version of them ;). Shouldn't be
too hard.

> I'd bet on lack of tuits. Anything with text has to deal with
> collation issues, etc., that may make this trickier than it first
> appears.

I don't see how collations makes things more complicated here.

- Andres