Re: [HACKERS] Block level parallel vacuum

On Wed, Dec 18, 2019 at 6:02 PM Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
>
> On Wed, Dec 18, 2019 at 3:36 PM Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
> >
> > Few other comments which I have not fixed:
> >
>
> + /* interface function to support parallel vacuum */
> + amestimateparallelvacuum_function amestimateparallelvacuum; /*
> can be NULL */
> } IndexAmRoutine;
>
> One more thing, why have you removed the estimate function for API
> patch?
>

Again thinking about this, it seems to me what you have done here is
probably the right direction because whatever else we will do we need
to have some untested code or we need to write/enhance some IndexAM to
test this. The point is that we don't have any IndexAM in the core
(after working around Gist index) which has this requirement and we
have not even heard from anyone of such usage, so there is a good
chance that whatever we do might not be sufficient for the IndexAM
that have such usage.

Now, we are already providing an option that one can set
VACUUM_OPTION_NO_PARALLEL to indicate that the IndexAM can't
participate in a parallel vacuum. So, I feel if there is any IndexAM
which would like to pass more data along with IndexBulkDeleteResult,
they can use that option. It won't be very difficult to enhance or
provide the new APIs to support a parallel vacuum if we come across
such a usage. I think we should just modify the comments atop
VACUUM_OPTION_NO_PARALLEL to mention this. I think this should be
good enough for the first version of parallel vacuum considering we
are able to support a parallel vacuum for all in-core indexes.

Thoughts?

--
With Regards,
Amit Kapila.
EnterpriseDB: http://www.enterprisedb.com