Date: Thu, 26 Oct 2017 14:45:15 -0500
From: Justin Pryzby <pryzby@telsasoft.com>
To: johannes =?iso-8859-1?Q?gra=EBn?= <johannes@selfnet.de>
Cc: Pavel Stehule <pavel.stehule@gmail.com>,
	"pgsql-performance@postgresql.org" <pgsql-performance@postgresql.org>
Subject: Re: performance drop after upgrade (9.6 > 10)
Message-ID: <20171026194515.GV21735@telsasoft.com>
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On Tue, Oct 24, 2017 at 04:15:59PM +0200, johannes graën wrote:
> Hi Pavel, *,
> 
> you were right with ANALYZing the DB first. However, even after doing
> so, I frequently see Seq Scans where an index was used before. This
> usually cooccurs with parallelization and looked different before
> upgrading to 10. I can provide an example for 10 [1], but I cannot
> generate a query plan for 9.6 anymore.
> 
> Any ideas what makes the new version more seqscanny?

Is it because max_parallel_workers_per_gather now defaults to 2 ?

BTW, I would tentatively expect a change in default to be documented in the
release notes but can't see that it's.
77cd477c4ba885cfa1ba67beaa82e06f2e182b85

Justin


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