Re: Pruning never visible changes

Simon Riggs <simon(dot)riggs(at)enterprisedb(dot)com> writes:
> On Fri, 16 Sept 2022 at 15:26, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>> You cannot
>> do that, at least not without checking that the originating
>> transaction has no snapshots that could see the older row version.

> I'm saying this is possible only AFTER the end of the originating
> xact, so there are no issues with additional snapshots.

I see, so the point is just that we can prune even if the originating
xact hasn't yet passed the global xmin horizon. I agree that's safe,
but will it fire often enough to be worth the trouble? Also, why
does it need to be restricted to certain shapes of HOT chains ---
that is, why can't we do exactly what we'd do if the xact *were*
past the xmin horizon?

regards, tom lane