Re: Further cleanup related to statistics import support in postgres_fdw

On Fri, Sep 4, 2026 at 8:34 PM Fujii Masao <masao(dot)fujii(at)gmail(dot)com> wrote:
> After the patch was committed, I observed that stats import could fail with
> the following warning even though the remote table is no longer
> inherited. Is this behavior intentional?
>
> WARNING: could not import statistics for foreign table
> "public.ft" --- remote table "public.t" is inherited
>
> Here is the procedure to reproduce this situation. The point is that
> the inheritance table is created and then dropped:
>
> --------------------------------
> CREATE TABLE t AS SELECT i FROM generate_series(1, 100) i;
> ANALYZE t;
> CREATE TABLE tt () INHERITS (t);
> DROP TABLE tt;
>
> CREATE EXTENSION postgres_fdw;
> CREATE SERVER loopback FOREIGN DATA WRAPPER postgres_fdw;
> CREATE USER MAPPING FOR public SERVER loopback;
> CREATE FOREIGN TABLE ft (i int) SERVER loopback OPTIONS (table_name
> 't', import_stats 'true');
>
> ANALYZE VERBOSE ft;
> WARNING: could not import statistics for foreign table "public.ft"
> --- remote table "public.t" is inherited
> --------------------------------

This is expected behavior, because postgres_fdw determines whether the
remote table is inherited or not, by checking only the table's
relhassubclass. We could check pg_inherits as well, to detect false
positives like this, but I didn't do so, because I don't think that
that is worth complicating the code, as table inheritance is not that
popular these days in the first place. Should we? I think another
option would be to add a note about this behavior.

Thanks for testing this!

Best regards,
Etsuro Fujita