Re: Adding clarification to description of IPC wait events XactGroupUpdate and ProcArrayGroupUpdate

Thanks for responding.

On Wed, Aug 14, 2024 at 10:29 PM Nathan Bossart <nathandbossart(at)gmail(dot)com>
wrote:

> On Thu, Jul 25, 2024 at 11:13:39AM +0800, SAMEER KUMAR wrote:
> > While preparing for my presentation on PostgreSQL Wait Events at
> > PgConf India, I was trying to understand *IPC:XactGroupUpdate* in more
> > detail. PostgreSQL documentation [1] mentions:
> >
> >> A process is waiting for the group leader to update the transaction
> status at the end of a _parallel operation_.
> >
> > I looked at `TransactionGroupUpdateXidStatus` in PostgreSQL code
> (`clog.c`)
> > Line `481` [2] sets this wait event.
> >
> > And after reading the code, my understanding is - It does not
> > necessarily need to be a "_parallel operation_". Or maybe I am just
> > misinterpreting "parallel operation" in this context. But it is
> > possible for other users to confuse it with the parallel query (and
> > parallel workers) feature.
> >
> > [...]
> >
> > We can add more clarity on what this wait event means. A similar
> > change should be done for `ProcArrayGroupUpdate` to indicate that the
> > wait event is a result of concurrent backend processes trying to clear
> > the transaction id (instead of saying "parallel operation").
>
> Both of these wait events had descriptions similar to what you are
> proposing when they were first introduced (commits d4116a7 and baaf272),
> but they were changed to the current wording by commit 3048898. I skimmed
> through the thread for the latter commit [0] but didn't see anything that
> explained why it was changed.
>

Yes, while reviewing the history of changes, I too noticed the same. The
documentation of older versions (v12 [1]) still has old descriptions.

>
> [0] https://postgr.es/m/21247.1589296570%40sss.pgh.pa.us
>
> --
> nathan
>

[1]
https://www.postgresql.org/docs/12/monitoring-stats.html#WAIT-EVENT-TABLE