I wrote:
> Yeah, this looks like exactly what I had in mind for HEAD. I'm not too
> sure about the back branches though. I think we could apply all of it
> to 8.3, but further back is going to require a separate investigation
> for each branch. Will you take that on?
BTW, I did a quick look at all the uses of RecentGlobalXmin in the back
branches, and I think we might be all right before 8.2. The older
branches do in fact init RecentGlobalXmin to InvalidTransactionId,
and the only thing they use it for is "is this tuple dead to everyone"
tests. Since InvalidTransactionId compares older than anything else,
the only consequence of not having set it is overly-conservative
decisions not to mark tuples killed. So unless you see a problem I
missed, I think we only have an issue-worth-fixing in 8.2 and 8.3.
regards, tom lane