Re: Something is wrong with wal_compression

On Fri, 2023-01-27 at 16:15 +1300, Thomas Munro wrote:
> On Fri, Jan 27, 2023 at 3:04 PM Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> > Thomas Munro <thomas(dot)munro(at)gmail(dot)com> writes:
> > > On Fri, Jan 27, 2023 at 1:30 PM Michael Paquier <michael(at)paquier(dot)xyz> wrote:
> > > > My opinion would be to make this function more reliable, FWIW, even if
> > > > that involves a performance impact when called in a close loop by
> > > > forcing more WAL flushes to ensure its report durability and
> > > > consistency.
> >
> > > Yeah, the other thread has a patch for that.  But it would hurt some
> > > workloads.
> >
> > I think we need to get the thing correct first and worry about
> > performance later.  What's wrong with simply making pg_xact_status
> > write and flush a record of the XID's existence before returning it?
> > Yeah, it will cost you if you use that function, but not if you don't.
>
> There is no
> doubt that the current situation is unacceptable, though, so maybe we
> really should just do it and make a faster one later.  Anyone else
> want to vote on this?

I wasn't aware of the existence of pg_xact_status, so I suspect that it
is not a widely known and used feature. After reading the documentation,
I'd say that anybody who uses it will want it to give a reliable answer.
So I'd agree that it is better to make it more expensive, but live up to
its promise.

Yours,
Laurenz Albe