Date: Tue, 12 May 2020 19:30:56 -0400
From: Bruce Momjian <bruce@momjian.us>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: "David G. Johnston" <david.g.johnston@gmail.com>, yigongh@gmail.com,
	pgsql-docs@lists.postgresql.org
Subject: Re: The suggestion of reducing autovacuum_vacuum_cost_delay should
 be documented
Message-ID: <20200512233056.GF4666@momjian.us>
References: <158927918783.656.11973436145559215458@wrigleys.postgresql.org>
 <20200512214014.GD4666@momjian.us>
 <20200512214101.GA21408@momjian.us>
 <CAKFQuwY+RMFFM1Y44=2dpi_8TyTq_4yrLUG6VjWnzgQAhG6o7Q@mail.gmail.com>
 <20200512224520.GE4666@momjian.us>
 <23940.1589325967@sss.pgh.pa.us>
MIME-Version: 1.0
Content-Type: text/plain; charset=iso-8859-1
Content-Disposition: inline
Content-Transfer-Encoding: 8bit
In-Reply-To: <23940.1589325967@sss.pgh.pa.us>
User-Agent: Mutt/1.10.1 (2018-07-13)
Precedence: bulk

On Tue, May 12, 2020 at 07:26:07PM -0400, Tom Lane wrote:
> Bruce Momjian <bruce@momjian.us> writes:
> > On Tue, May 12, 2020 at 03:38:16PM -0700, David G. Johnston wrote:
> >> The proposal is to document in versions 9.4 to 11 that the recommended value
> >> for the setting is 2ms while for reasons of continuity the default in these
> >> versions is 20ms.
> >> I don't really see any harm in it.  Its not like the choice to reduce the value
> >> was made because of new features introduced in 12 - it was a re-evaluation of a
> >> 15 year old default.
> 
> > Well, we really need to have some general discussion about whether
> > changing defaults in major releases should trigger a mention to change
> > the defaults in back branches.  This is something that would have to be
> > discussed on the hackers list.
> 
> It's not immediately obvious that the new default value established in
> version N is appropriate for version N-minus-several.  Certainly, whatever
> testing was done to justify the new default wouldn't have been done on old
> versions; and there might have been relevant changes.
> 
> In short: nope, I'm not on board with blindly back-patching such
> recommendations.

That was my analysis too.

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

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