Date: Sat, 3 Apr 2021 11:12:01 -0400
From: Bruce Momjian <bruce@momjian.us>
To: aditya desai <admad123@gmail.com>
Cc: Justin Pryzby <pryzby@telsasoft.com>,
	Pgsql Performance <pgsql-performance@lists.postgresql.org>
Subject: Re: SELECT Query taking 200 ms on PostgreSQL compared to 4 ms on
 Oracle after migration.
Message-ID: <20210403151201.GD29125@momjian.us>
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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.

---------------------------------------------------------------------------

> 
> Regards,
> Aditya.
> 
> On Sat, Apr 3, 2021 at 7:46 PM Justin Pryzby <pryzby@telsasoft.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@gmail.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@momjian.us>        https://momjian.us
  EDB                                      https://enterprisedb.com

  If only the physical world exists, free will is an illusion.