Date: Sun, 28 Jan 2018 18:53:10 -0500
From: Bruce Momjian <bruce@momjian.us>
To: Justin Pryzby <pryzby@telsasoft.com>
Cc: johannes =?iso-8859-1?Q?gra=EBn?= <johannes@selfnet.de>,
	Pavel Stehule <pavel.stehule@gmail.com>,
	"pgsql-performance@postgresql.org" <pgsql-performance@postgresql.org>
Subject: Re: [PERFORM] performance drop after upgrade (9.6 > 10)
Message-ID: <20180128235310.GA5024@momjian.us>
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On Thu, Oct 26, 2017 at 02:45:15PM -0500, Justin Pryzby wrote:
> 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

Oops, you are correct.  The PG 10 release notes, which I wrote, should
have mentioned this.  :-(

	https://www.postgresql.org/docs/10/static/release-10.html

-- 
  Bruce Momjian  <bruce@momjian.us>        http://momjian.us
  EnterpriseDB                             http://enterprisedb.com

+ As you are, so once was I.  As I am, so you will be. +
+                      Ancient Roman grave inscription +