Re: Bug in autovacuum.c?

Bruce Momjian wrote:
> > Yeah, I think this change would have the effect of moving the freeze
> > limit by one (or two?) counts.  Given the moving nature of values
> > returned by ReadNewTransactionId this would probably have no practical
> > effect.  Still, the code as is seems more natural to me (Tom wrote this
> > bit IIRC, not me).
> 
> I am now thinking the code is correct --- it maps values from 0 to
> FirstNormalTransactionId into the top of the (unsigned) xid range. 
> Unless someone objects, I will add a C comment about this behavior so
> future readers are not confused.

OK, now I think it is wrong.   :-)

The effect is to map max xid + 1 to max xid -
FirstNormalTransactionId(3) + 1, which makes the xid look like it is
going backwards, less than max xid --- not good.

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

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