Re: vacuum verbose no longer reveals anything about pins

On Thu, Jun 30, 2022 at 11:33 AM Peter Geoghegan <pg(at)bowt(dot)ie> wrote:
> On Thu, Jun 30, 2022 at 5:57 AM Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
> > I was dismayed to learn that VACUUM VERBOSE on a table no longer tells
> > you anything about whether any pages were skipped due to pins.
>
> VACUUM VERBOSE will show a dedicated line that reports on the number
> of pages that we couldn't get a cleanup lock on, if and only if we
> couldn't do useful work as a result. In practice this means pages that
> had one or more fully DEAD tuples that couldn't be removed due to our
> inability to prune. In my view this is strictly better than reporting
> on the number of "skipped due to pins" pages.

Ah, I missed that. I think that in the test case I was using, there
was a conflicting pin but there were no dead tuples, so that line
wasn't present in the output.

> In the case of any pages that we couldn't get a cleanup lock on that
> didn't have any DEAD tuples (pages that are not reported on at all),
> VACUUM hasn't missed any work whatsoever. It even does heap vacuuming,
> which doesn't require a cleanup lock in either the first or the second
> heap pass. What's the problem with not reporting on that?

Maybe nothing. I just thought you'd completely removed all reporting
on this, and I'm glad that's not so.

Thanks for the quick response.

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