Re: Bug in autovacuum.c?

Tom Lane wrote:
> Robert Haas <robertmhaas@gmail.com> writes:
> > On Fri, Apr 1, 2011 at 5:48 PM, Bruce Momjian <bruce@momjian.us> wrote:
> >> Agreed it is not worth it but I think we should at least C comment
> >> something.  I think at a minimum we should set it to
> >> FirstNormalTransactionId.
> 
> > I think you should leave it well enough alone.
> 
> Yes.  The point of the existing coding is to ensure that we don't
> overestimate the table age at which vacuums should be forced.
> Bruce's proposed change would move the inaccuracy in the wrong
> direction, and thus cause some cases to not force autovac though an
> exact calculation would have done so.  It's not worth trying to be
> exactly correct here, but I don't think that we want to err in
> that direction.
> 
> If we had a symbol for the max normal XID, we could instead code
> like this:
> 
>     if (xidForceLimit < FirstNormalTransactionId)
>         xidForceLimit = LastNormalTransactionId;
> 
> But AFAIR we don't, and I don't especially want to introduce one,
> because people might be misled by it.  As you mentioned earlier,
> the XID space is circular so there isn't really a "last" XID.

Sorry for the late reply but it seems HighestNormalTransactionId might
be an apporopriate name.  However, it is not code I normally deal with
so unless someone who works in this area wants to make this cleanup, I
will ignore the issue.

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

  + It's impossible for everything to be true. +