RE: Partial aggregates pushdown

Hi Mr.Momjian.

> > There is one more thing I would like your opinion on.
> > As the major version of PostgreSQL increase, it is possible that the
> > new builtin aggregate functions are added to the newer PostgreSQL.
> > This patch assume that aggpartialfns definitions exist in BKI files.
> > Due to this assumption, someone should add aggpartialfns definitions of
> new builtin aggregate functions to BKI files.
> > There are two possible ways to address this issue. Would the way1 be
> sufficient?
> > Or would way2 be preferable?
> > way1) Adding documentaion for how to add these definitions to BKI files
> > way2) Improving this patch to automatically add these definitions to BKI
> files by some tool such as initdb.
>
> I think documentation is sufficient. You already showed that someone can do
> this with CREATE AGGREGATE for non-builtin aggregates.
Thank you for your opinion. I will modify this patch according to the way1.

> > > So, let's remove the PARTIALAGG_MINVERSION option from the patch and
> > > just make it automatic --- we push down builtin partial aggregates
> > > if the remote server is the same or newer _major_ version than the
> > > sending server. For extensions, if people have older extensions on
> > > the same or newer foreign servers, they can adjust 'extensions' above.
> > Okay, I understand. I will remove PARTIALAGG_MINVERSION option from
> > the patch and I will add check whether aggpartialfn depends on some
> > extension which is containd in extensions list of the postgres_fdw's foreign
> server.
>
> Yes, good. Did we never push down aggregates before? I thought we
> pushed down partitionwise aggregates already, and such a check should
> already be done. If the check isn't there, it should be.
Yes. The last version of this patch(and original postgres_fdw) checks if
user-defined aggregate depends some extension which is contained in 'extensions'.
But, in the last version of this patch, there is no such check for
aggpartialfn of user-defined aggregate. So, I will add such check to this patch.
I think that this modification is easy to do .

> In summary, we don't do any version check for built-in function pushdown, so
> we don't need it for aggregates either. We check extension functions against
> the extension pushdown list, so we should be checking this for partial
> aggregate pushdown, and for partition-wise aggregate pushdown. If we don't
> do that last check already, it is a bug.
I understood.

Sincerely yours,
Yuuki Fujii

--
Yuuki Fujii
Information Technology R&D Center Mitsubishi Electric Corporation