Re: Data is copied twice when specifying both child and parent table in publication

On Tue, Apr 19, 2022 at 2:23 PM shiy.fnst@fujitsu.com
<shiy.fnst@fujitsu.com> wrote:
>
> On Tue, Apr 19, 2022 3:05 PM houzj.fnst@fujitsu.com <houzj.fnst@fujitsu.com> wrote:
> >
> > One suggestion is that can we simplify the code by moving the logic of checking
> > the ancestor into the SQL ?. For example, we could filter the outpout of
> > pg_publication_tables by adding A WHERE clause which checks whether the table
> > is a partition and if its ancestor is also in the output. I think we can also
> > filter the needless partition in this approach.
> >
>
> I agreed with you and I tried to fix this problem in a simpler way. What we want
> is to exclude the partitioned table whose ancestor is also need to be
> replicated, so how about implementing that by using the following SQL when
> getting the table list from publisher?
>
> SELECT DISTINCT ns.nspname, c.relname
> FROM pg_catalog.pg_publication_tables t
> JOIN pg_catalog.pg_namespace ns ON ns.nspname = t.schemaname
> JOIN pg_catalog.pg_class c ON c.relname = t.tablename AND c.relnamespace = ns.oid
> WHERE t.pubname IN ('p0','p2')
> AND (c.relispartition IS FALSE OR NOT EXISTS (SELECT 1 FROM pg_partition_ancestors(c.oid)
> WHERE relid IN ( SELECT DISTINCT (schemaname||'.'||tablename)::regclass::oid
> FROM pg_catalog.pg_publication_tables t
> WHERE t.pubname IN ('p0','p2') ) AND relid != c.oid));
>
> Please find the attached patch which used this approach, I also merged the test
> in Wang's patch into it.
>

I think this will work but do we need "... relid != c.oid" at the end
of the query? If so, why? Please use an alias for
pg_partition_ancestors to make the statement understandable.

Now, this solution will work but I find this query a bit complex and
will add some overhead as we are calling pg_publication_tables
multiple times. So, I was wondering if we can have a new function
pg_get_publication_tables which takes multiple publications as input
and return the list of qualified tables? I think for back branches we
need something on the lines of what you have proposed but for HEAD we
can have a better solution.

IIRC, the column list and row filter also have some issues exactly due
to this reason, so, I would like those cases to be also mentioned here
and probably include the tests for them in the patch for HEAD.

-- 
With Regards,
Amit Kapila.