Re: wait event and archive_command

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.

Regards,
Bharath Rupireddy.