Re: The vacuum-ignore-vacuum patch

Tom Lane wrote:
> Alvaro Herrera <alvherre@commandprompt.com> writes:
> > Tom Lane wrote:
> >> nonInVacuumXmin seems useless ... perhaps a vestige of some earlier
> >> version of the computation?
> 
> > Hmm, not useless at all really -- only a bug of mine.  Turns out the
> > notInVacuumXmin stuff is essential, so I put it back.
> 
> Uh, why?

Because it's used to determine the Xmin that our vacuum will use.  If
there is a transaction whose Xmin calculation included the Xid of a
transaction running vacuum, we have gained nothing from directly
excluding said vacuum's Xid, because it will affect us anyway indirectly
via that transaction's Xmin.

-- 
Alvaro Herrera                                http://www.CommandPrompt.com/
The PostgreSQL Company - Command Prompt, Inc.