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

On Wed, Jun 7, 2017 at 10:55 PM, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
> On Tue, Jun 6, 2017 at 3:23 PM, David Fetter <david(at)fetter(dot)org> wrote:
>> I'd bet on lack of tuits.
>
> I expect that was part of it. Another thing to consider is that, for
> numeric aggregates, the transition values don't generally get larger
> as you aggregate, but for something like string_agg(), they will.
> It's not clear how much work we'll really save by parallelizing that
> sort of thing. Maybe it will be great?

+1, I was thinking about the same. There might be some cases when the
output of array_agg/string_agg is not a lot wider but the underlying
scans are large e.g. having clause containing another aggregate and
very small group sizes. I am not sure how frequent are such usecases.

--
Best Wishes,
Ashutosh Bapat
EnterpriseDB Corporation
The Postgres Database Company