From: Tom Lane <tgl@sss.pgh.pa.us>
To: Bruce Momjian <bruce@momjian.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
In-reply-to: <20200512224520.GE4666@momjian.us>
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 <20200512224520.GE4666@momjian.us>
Comments: In-reply-to Bruce Momjian <bruce@momjian.us>
	message dated "Tue, 12 May 2020 18:45:20 -0400"
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Date: Tue, 12 May 2020 19:26:07 -0400
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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 t=
hese
>> versions is 20ms.
>> I don't really see any harm in it.=C2=A0 Its not like the choice to red=
uce the value
>> was made because of new features introduced in 12 - it was a re-evaluat=
ion 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.

			regards, tom lane