Re: wait event and archive_command

On Wed, Nov 10, 2021 at 5:00 PM Bharath Rupireddy
<bharath(dot)rupireddyforpostgres(at)gmail(dot)com> wrote:
>
> On Mon, Nov 1, 2021 at 2:31 PM Fujii Masao <masao(dot)fujii(at)oss(dot)nttdata(dot)com> wrote:
> > > The following activitymsg that are being set to ps display in
> > > XLogFileRead and pgarch_archiveXlog have come up for one of our
> > > internal team discussions recently:
> > >
> > > snprintf(activitymsg, sizeof(activitymsg), "waiting for %s",
> > > xlogfname);
> > > set_ps_display(activitymsg);
> > >
> > > snprintf(activitymsg, sizeof(activitymsg), "recovering %s",
> > > xlogfname);
> > > set_ps_display(activitymsg);
> > >
> > > snprintf(activitymsg, sizeof(activitymsg), "archiving %s", xlog);
> > > set_ps_display(activitymsg);
> > >
> > > The ps display info might be useful if we run postgres on a stand
> > > alone box and there's someone monitoring at the ps output, but it
> > > doesn't help debugging after an issue has occurred. How about we have
> > > the following statements which will be useful for someone to look at
> > > the server logs and know what was/is happening during the recovery and
> > > archiving.
> >
> > If an issue occurs while the command is executing,
> > the error message is logged, isn't it? Isn't that enough for your case?
>
> You are right when an issue occurs. However, these messages will be
> useful 1) if the recovery or archiving is taking a lot of time and one
> would want to understand how it is progressing. 2) if these commands
> pass but an issue occurs in some other area of the code. IMO, we
> should have these as LOG messages instead of just setting in the ps
> display for temporary purposes which doesn't work well with the
> postgres on cloud where users/admins/developers don't get to see the
> ps display.
>
> > > IMO, we should also have the elog statement.
> > >
> > > elog(LOG, "waiting for %s", xlogfname);
> > > elog(LOG, "recovering %s"", xlogfname);
> > > elog(LOG, "archiving %s", xlog);
> >
> > I'm afraid that some people think that it's noisy to always log those messages.
>
> I don't think these are noisy messages at all. In fact, they will be
> useful to answer (if not exact answers, but an approximation) some of
> the customer queries like "what is happening in my server during the
> recovery/archiving phase? how much more time recovery might take?".
> Today, the server emits lot of LOGs, adding these will not blow up the
> server logs at all if the log rotation policy is configured
> appropriately.
>
> Having said the above, I plan to discuss these things in a separate thread.

Just for the records - I've started a new thread for the above
discussion - https://www.postgresql.org/message-id/CALj2ACUfMU%3Dahxivfy%2BZmpVZccd5PASG-_10mLpM55_Y_h4-VA%40mail.gmail.com

Regards,
Bharath Rupireddy.