Re: GetCurrentVirtualXIDs()

Simon Riggs  writes:
> No need to wait for idle-in-transaction sessions during index builds.
> GetCurrentVirtualXIDs() specifically *includes* backends that have
> proc->xmin == InvalidTransactionId (0), but I'm not sure why.

Applied with the discussed tweaks.  I also added some logic to make
DefineIndex recheck the GetCurrentVirtualXIDs output each time it is
about to wait for another session.  If we observe some other session
to have xmin = 0 at any one of those instants, we don't have to
wait for it.  Not sure how much that will really help in practice,
but it can't hurt.
		regards, tom lane