Re: xact_start for walsender & logical decoding not updated

On Wed, 11 Dec 2019 at 02:08, Alvaro Herrera <alvherre@2ndquadrant.com>
wrote:

> On 2019-Dec-10, Tomas Vondra wrote:
>
> > On Tue, Dec 10, 2019 at 09:42:17AM +0900, Kyotaro Horiguchi wrote:
> > > At Tue, 10 Dec 2019 00:44:09 +0100, Tomas Vondra <
> tomas.vondra@2ndquadrant.com> wrote in
>
> > > I'm not sure how much xact_start for walsender is useful and we really
> > > is not running a statement there.  Also autovac launcher starts
> > > transaction without a valid statement timestamp perhaps for the same
> > > reason.
> >
> > Maybe, but then maybe we should change it so that we don't report any
> > timestamps for such processes.
>
> Yeah, I think we should to that.


Agreed. Don't report a transaction start timestamp at all if we're not in a
read/write txn in the walsender, which we should never be when using a
historic snapshot.

It's not interesting or relevant.

Reporting the commit timestamp of the current or last-processed xact would
likely just be fonfusing. I'd rather see that in pg_stat_replication if
we're going to show it, that way we can label it usefully.

-- 
 Craig Ringer                   http://www.2ndQuadrant.com/
 2ndQuadrant - PostgreSQL Solutions for the Enterprise