Re: Unable to test parallel aggregate/joins in Postgres beta 2

On Thu, Jul 14, 2016 at 7:09 PM, Haribabu Kommi <kommi(dot)haribabu(at)gmail(dot)com>
wrote:

> On Thu, Jul 14, 2016 at 11:16 PM, Madusudanan.B.N
> <b(dot)n(dot)madusudanan(at)gmail(dot)com> wrote:
> >
> > 3) Is there any kind of toggle to enable parallel aggregate/join feature
> ?
> >
>
> I am able to generate parallel plan, The parallel plan may be costly
> in your query compared
> to other scans, because of which it is not selecting the parallel plan.
>
> It is possible that if the table size is very small or you are
> selecting all records of the table
> and etc.
>
> postgres=# insert into test values(generate_series(1,1000000), 'Test');
> INSERT 0 1000000
> postgres=# explain select * from test where f1 < 9900;
> QUERY PLAN
>
> -----------------------------------------------------------------------------
> Gather (cost=1000.00..23719.93 rows=188964 width=105)
> Workers Planned: 2
> -> Parallel Seq Scan on test (cost=0.00..22719.93 rows=78735
> width=105)
> Filter: (f1 < 9900)
> (4 rows)
>

For the above example, I can see that it does choose parallel plan.
However as said above, for other cases it does not choose a parallel plan.

Is there any other considerations apart from the mentioned ones on why pg
would not choose a parallel plan ?

>
>
> Regards,
> Hari Babu
> Fujitsu Australia
>

--
Regards,
Madusudanan.B.N <http://madusudanan.com>