Re: Add index scan progress to pg_stat_progress_vacuum

On Thu, May 26, 2022 at 11:43 AM Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com> wrote:
> Another idea I came up with is that we can wait for all index vacuums
> to finish while checking and updating the progress information, and
> then calls WaitForParallelWorkersToFinish after confirming all index
> status became COMPLETED. That way, we don’t need to change the
> parallel query infrastructure. What do you think?

+1 from me. It doesn't seem to me that we should need to add something
like parallel_vacuum_progress_callback in order to solve this problem,
because the parallel index vacuum code could just do the waiting
itself, as you propose here.

The question Sami asks him his reply is a good one, though -- who is
to say that the leader only needs to update progress at the end, once
it's finished the index it's handling locally? There will need to be a
callback system of some kind to allow the leader to update progress as
other workers finish, even if the leader is still working. I am not
too sure that the idea of using the vacuum delay points is the best
plan. I think we should try to avoid piggybacking on such general
infrastructure if we can, and instead look for a way to tie this to
something that is specific to parallel vacuum. However, I haven't
studied the problem so I'm not sure whether there's a reasonable way
to do that.

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