Re: parallel distinct union and aggregate support patch

On Tue, Oct 27, 2020 at 5:43 PM Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
>
> On Thu, Oct 22, 2020 at 5:08 AM Dilip Kumar <dilipbalaut(at)gmail(dot)com> wrote:
> > Interesting idea. So IIUC, whenever a worker is scanning the tuple it
> > will directly put it into the respective batch(shared tuple store),
> > based on the hash on grouping column and once all the workers are
> > doing preparing the batch then each worker will pick those baches one
> > by one, perform sort and finish the aggregation. I think there is a
> > scope of improvement that instead of directly putting the tuple to the
> > batch what if the worker does the partial aggregations and then it
> > places the partially aggregated rows in the shared tuple store based
> > on the hash value and then the worker can pick the batch by batch. By
> > doing this way, we can avoid doing large sorts. And then this
> > approach can also be used with the hash aggregate, I mean the
> > partially aggregated data by the hash aggregate can be put into the
> > respective batch.
>
> I am not sure if this would be a win if the typical group size is
> small and the transition state has to be serialized/deserialized.
> Possibly we need multiple strategies, but I guess we'd have to test
> performance to be sure.

+1

--
Regards,
Dilip Kumar
EnterpriseDB: http://www.enterprisedb.com