Re: SELECT Query taking 200 ms on PostgreSQL compared to 4 ms on Oracle after migration.

On Sat, Apr 3, 2021 at 08:38:18PM +0530, aditya desai wrote:
> Hi Justin,
> Yes, force_parallel_mode is on. Should we set it off?

Yes. I bet someone set it without reading our docs:

https://www.postgresql.org/docs/13/runtime-config-query.html#RUNTIME-CONFIG-QUERY-OTHER

--> Allows the use of parallel queries for testing purposes even in cases
--> where no performance benefit is expected.

We might need to clarify this sentence to be clearer it is _only_ for
testing. Also, I suggest you review _all_ changes that have been made
to the server since I am worried other unwise changes might also have
been made.

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>
> Regards,
> Aditya.
>
> On Sat, Apr 3, 2021 at 7:46 PM Justin Pryzby <pryzby(at)telsasoft(dot)com> wrote:
>
> On Sat, Apr 03, 2021 at 04:08:01PM +0200, Pavel Stehule wrote:
> > so 3. 4. 2021 v 15:38 odesílatel aditya desai <admad123(at)gmail(dot)com>
> napsal:
> > > "Gather (cost=1000.43..1002.75 rows=1 width=127) (actual
> > > time=174.318..198.539 rows=1 loops=1)"
> > > " Workers Planned: 1"
> > > " Workers Launched: 1"
> > > " Single Copy: true"
> > > " -> Index Scan using address1_i7 on address1 dom (cost=0.43..2.65 rows
> =1
> > > width=127) (actual time=0.125..0.125 rows=1 loops=1)"
> > > " Index Cond: (address_key = 6113763)"
> > > "Planning Time: 0.221 ms"
> > > "Execution Time: 198.601 ms"
> >
> > You should have broken configuration - there is not any reason to start
> > parallelism -  probably some option in postgresql.conf has very bad
> value.
> > Second - it's crazy to see 200 ms just on interprocess communication -
> > maybe your CPU is overutilized.
>
> It seems like force_parallel_mode is set, which is for debugging and not
> for
> "forcing things to go faster".  Maybe we should rename the parameter, like
> parallel_mode_testing=on.
>
> http://rhaas.blogspot.com/2018/06/using-forceparallelmode-correctly.html
>
> --
> Justin
>

--
Bruce Momjian <bruce(at)momjian(dot)us> https://momjian.us
EDB https://enterprisedb.com

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