Re: Add 64-bit XIDs into PostgreSQL 15

On Mon, Nov 28, 2022 at 1:52 PM Bruce Momjian <bruce(at)momjian(dot)us> wrote:
> I think the problem is that we still have bloat with 64-bit XIDs,
> specifically pg_xact and pg_multixact files. Yes, that bloat is less
> serious, but it is still an issue worth reporting in the server logs,
> though not serious enough to stop the server from write queries.

That's definitely a big part of it.

Again, I don't believe that the idea is fundamentally without merit.
Just that it's not worth it, given that having more XID space is very
much not something that I think fixes most of the problems. And given
the real risk of serious bugs with something this invasive.

I believe that it would be more useful to focus on just not getting
into trouble in the first place, as well as on mitigating specific
problems that lead to the system reaching xidStopLimit in practice. I
don't think that there is any good reason to allow datfrozenxid to go
past about a billion. When it does the interesting questions are
questions about what went wrong, and how that specific failure can be
mitigated in a fairly direct way.

We've already used way to much "XID space runway", so why should using
even more help? It might, I suppose, but it almost seems like a
distraction to me, as somebody that wants to make things better for
users in general. As long as the system continues to misbehave (in
whatever way it happens to be misbehaving), why should any amount of
XID space ever be enough?

I think that we'll be able to get rid of freezing in a few years time.
But as long as we have freezing, we have these problems.

--
Peter Geoghegan