Re: Set access strategy for parallel vacuum workers

On Thu, Apr 8, 2021 at 8:44 AM Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
>
> On Wed, Apr 7, 2021 at 7:12 PM Bharath Rupireddy
> <bharath(dot)rupireddyforpostgres(at)gmail(dot)com> wrote:
> >
> > On Wed, Apr 7, 2021 at 3:30 PM Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
> > >
> > > During recent developments in the vacuum, it has been noticed [1] that
> > > parallel vacuum workers don't use any buffer access strategy. I think
> > > we can fix it either by propagating the required information from the
> > > leader or just get the access strategy in each worker separately. The
> > > patches for both approaches for PG-13 are attached.
> > >
> > > Thoughts?
> > >
> > > [1] - https://www.postgresql.org/message-id/CAH2-Wz%3Dgf6FXW-jPVRdeCZk0QjhduCqH_XD3QbES9wPmhircuA%40mail.gmail.com
> >
> > Note: I have not followed the original discussion in [1].
> >
> > My understanding of the approach #1 i.e. propagating the vacuum
> > strategy down to the parallel vacuum workers from the leader is that
> > the same ring buffer (of 256KB for vacuum) will be used by both leader
> > and all the workers.
> >
>
> No that is not the intention, each worker will use its ring buffer.
> The first approach just passes the relevant information to workers so
> that they can use the same strategy as used by the leader but both
> will use separate ring buffer.

Thanks for the clarification. I understood now.

On the patch fix_access_strategy_workers_11.patch: can we have the
more descriptive comment like "/* Each parallel VACUUM worker gets its
own access strategy */" that's introduced by commit f6b8f19 instead of
just saying "/* Set up vacuum access strategy */" which is quite
obvious from the function name GetAccessStrategy?

With Regards,
Bharath Rupireddy.
EnterpriseDB: http://www.enterprisedb.com