From: Abadie Lana <Lana.Abadie@iter.org>
To: Justin Pryzby <pryzby@telsasoft.com>
CC: "pgsql-performance@lists.postgresql.org"
	<pgsql-performance@lists.postgresql.org>
Subject: RE: select query does not pick up the right index
Thread-Topic: select query does not pick up the right index
Thread-Index: AdSitwt5/9TyB7hoTX++E94tUlkiMv//9kOA//6cjtA=
Date: Thu, 3 Jan 2019 12:58:06 +0000
Message-ID: <92561fd0a0a846288cb0360ee0ae2505@iter.org>
References: <c2d19232595246018b277ebcd59a0046@iter.org>
 <20190102164525.GU25379@telsasoft.com>
In-Reply-To: <20190102164525.GU25379@telsasoft.com>
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Lana ABADIE
Database Engineer
CODAC Section

ITER Organization, Building 72/4108, SCOD, Control System Division
Route de Vinon-sur-Verdon - CS 90 046 - 13067 St Paul Lez Durance Cedex - F=
rance
Phone: +33 4 42 17 84 02
Get the latest ITER news on http://www.iter.org/whatsnew

-----Original Message-----
From: Justin Pryzby <pryzby@telsasoft.com>=20
Sent: 02 January 2019 17:45
To: Abadie Lana <Lana.Abadie@iter.org>
Cc: pgsql-performance@lists.postgresql.org
Subject: Re: select query does not pick up the right index

On Wed, Jan 02, 2019 at 04:28:41PM +0000, Abadie Lana wrote:
> css_archive_3_0_0=3D# explain analyze select t.name, c.smpl_time,c.nanose=
cs,c.float_val,c.num_                                                      =
                 val,c.str_val,c.datatype,c.array_val from sample c, channe=
l t where t.channel_id=3Dc.channel_i                                       =
                                d and t.name=3D'BUIL-B36-VA-RT-RT1:CL0001-2=
-ABW'   order by c.smpl_time desc limit 5;
>  QUERY PLAN
>=20
> -------------------------------------------------------------------------=
-------------------
> -------------------------------------------------------------------------=
-------------------
> -------------
> Gather  (cost=3D1004.71..125606.08 rows=3D5 width=3D150) (actual time=3D3=
8737.443..1220277.244 rows
> =3D3 loops=3D1)
>    Workers Planned: 1
>    Workers Launched: 1
>    Single Copy: true

Do you have force_parallel_mode set ?

http://rhaas.blogspot.com/2018/06/using-forceparallelmode-correctly.html

--=20
Justin Pryzby
System Administrator
Telsasoft
+1-952-707-8581


Hi Justin
Indeed force_parallel_mode was set to on. Even after disabling it, same iss=
ue...
cheers