Re: The suggestion of reducing autovacuum_vacuum_cost_delay should be documented

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.

            regards, tom lane