Re: [HACKERS] Block level parallel vacuum - Mailing list pgsql-hackers

On Tue, Oct 15, 2019 at 4:15 PM Masahiko Sawada <sawada.mshk@gmail.com> wrote:
>
> On Tue, Oct 15, 2019 at 3:55 PM Amit Kapila <amit.kapila16@gmail.com> wrote:
> >
> > On Tue, Oct 15, 2019 at 10:34 AM Masahiko Sawada <sawada.mshk@gmail.com> wrote:
> > >
> > > On Mon, Oct 14, 2019 at 6:37 PM Amit Kapila <amit.kapila16@gmail.com> wrote:
> > > >
> > >
> > > > 3. Do we really need to give the responsibility of deleting empty
> > > > pages (gistvacuum_delete_empty_pages) to gistvacuumcleanup.  Can't we
> > > > do it in gistbulkdelte?  I see one advantage of postponing it till the
> > > > cleanup phase which is if somehow we can accumulate stats over
> > > > multiple calls of gistbulkdelete, but I am not sure if it is feasible.
> > > > At least, the way current code works, it seems that there is no
> > > > advantage to postpone deleting empty pages till the cleanup phase.
> > > >
> > >
> > > Considering the current strategy of page deletion of gist index the
> > > advantage of postponing the page deletion till the cleanup phase is
> > > that we can do the bulk deletion in cleanup phase which is called at
> > > most once. But I wonder if we can do the page deletion in the similar
> > > way to btree index.
> > >
> >
> > I think there might be some advantage of the current strategy due to
> > which it has been chosen.  I was going through the development thread
> > and noticed some old email which points something related to this.
> > See [1].
>
> Thanks.
>
> >
> > > Or even we use the current strategy I think we can
> > > do that while not passing the pages information from bulkdelete to
> > > vacuumcleanup using by GistBulkDeleteResult.
> > >
> >
> > Yeah, I also think so.  I have started a new thread [2] to know the
> > opinion of others on this matter.
> >
>
> Thank you.
>
> > > > If we avoid postponing deleting empty pages till the cleanup phase,
> > > > then we don't have the problem for gist indexes.
> > >
> > > Yes. But considering your pointing out I guess that there might be
> > > other index AMs use the stats returned from bulkdelete in the similar
> > > way to gist index (i.e. using more larger structure of which
> > > IndexBulkDeleteResult is just the first field). If we have the same
> > > concern the parallel vacuum still needs to deal with that as you
> > > mentioned.
> > >
> >
> > Right, apart from some functions for memory allocation/estimation and
> > stats copy, we might need something like amcanparallelvacuum, so that
> > index methods can have the option to not participate in parallel
> > vacuum due to reasons similar to gist or something else.  I think we
> > can work towards this direction as this anyway seems to be required
> > and till we reach any conclusion for gist indexes, you can mark
> > amcanparallelvacuum for gist indexes as false.
>
> Agreed. I'll create a separate patch to add this callback and change
> parallel vacuum patch so that it checks the participation of indexes
> and then vacuums on un-participated indexes after parallel vacuum.

amcanparallelvacuum is not necessary to be a callback, it can be a
boolean field of IndexAmRoutine.

Regards,

--
Masahiko Sawada