Re: using custom scan nodes to prototype parallel sequential scan - Mailing list pgsql-hackers

On 12 November 2014 07:54, David Rowley <dgrowleyml@gmail.com> wrote:
> On Tue, Nov 11, 2014 at 9:29 PM, Simon Riggs <simon@2ndquadrant.com> wrote:
>>
>>
>> This plan type is widely used in reporting queries, so will hit the
>> mainline of BI applications and many Mat View creations.
>> This will allow SELECT count(*) FROM foo to go faster also.
>>
>
> We'd also need to add some infrastructure to merge aggregate states together
> for this to work properly. This means that could also work for avg() and
> stddev etc. For max() and min() the merge functions would likely just be the
> same as the transition functions.

Do you mean something like a "subtotal" or "intermediate combination" functon?

I guess we'd need the same thing to make intermediate aggregates work
during a sort?

-- Simon Riggs                   http://www.2ndQuadrant.com/PostgreSQL Development, 24x7 Support, Training & Services