Re: Parallel Aggregate

On 14 March 2016 at 17:05, James Sewell <james(dot)sewell(at)lisasoft(dot)com> wrote:
>
> Hi again,
>
> I've been playing around with inheritance combined with this patch. Currently it looks like you are taking max(parallel_degree) from all the child tables and using that for the number of workers.
>
> For large machines it makes much more sense to use sum(parallel_degree) - but I've just seen this comment in the code:
>
> /*
> * Decide what parallel degree to request for this append path. For
> * now, we just use the maximum parallel degree of any member. It
> * might be useful to use a higher number if the Append node were
> * smart enough to spread out the workers, but it currently isn't.
> */
>
> Does this mean that even though we are aggregating in parallel, we are only operating on one child table at a time currently?

There is nothing in the planner yet, or any patch that I know of to
push the Partial Aggregate node to below an Append node. That will
most likely come in 9.7.

--
David Rowley http://www.2ndQuadrant.com/
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