Re: Default setting for autovacuum_freeze_max_age

On Fri, Oct 21, 2016 at 10:44:41AM -0400, Tom Lane wrote:
> Bruce Momjian <bruce@momjian.us> writes:
> > Why is autovacuum_freeze_max_age's default set to 200 million, rather
> > than something like 2 billion?  It seems 2 billion is half way to
> > wrap-around and would be a better default.  Right now, the default seems
> > to freeze 10x more often than it has to.
> 
> Please see the archives.  I do not remember the reasoning, but there
> was some, and you need to justify why it was wrong not just assert
> that you think it's silly.

I think the reasoning was to avoid checking old clog files, but with
tuple transaction status bits, e.g. HEAP_XMIN_COMMITTED, which were
added long ago, I don't remember why either.  I remember asking years
ago and not getting a good answer, and giving up.

If no one can give an answer, I suggest we change the default.

-- 
  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. +
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