Alvaro Herrera <alvherre@commandprompt.com> writes:
> Tom Lane wrote:
>> 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.
But the patch changes things so that *everyone* excludes the vacuum from
their xmin. Or at least I thought that was the plan.
regards, tom lane