Re: Add last commit LSN to pg_last_committed_xact()

On Tue, Jan 18, 2022 at 9:47 AM James Coleman <jtc331(at)gmail(dot)com> wrote:
> > Well, if you're maintaining an SLRU, you do kind of need to know where
> > the leading and lagging ends are.
>
> As far as I can tell the data in commitTsShared is used purely as an
> optimization for the path looking up the timestamp for an arbitrary
> xid when that xid happens to be the most recent one so that we don't
> have to look up in the SLRU for that specific case. Maybe I'm missing
> something else you're seeing?

I wasn't looking at the code, but that use also seems closer to the
purpose of committs than your proposal.

> > As far as performance goes, I'm more concerned about Alvaro's patch.
> > My concern with this one is more around whether it's too much of a
> > kludge.
>
> As far as the kludginess factor: do you think additional GUCs would
> help clarify that? And/or are the earlier comments on the right path?

To be honest, I'm sort of keen to hear what other people think. I'm
shooting from the hip a little bit here...

--
Robert Haas
EDB: http://www.enterprisedb.com