On Tue, Dec 16, 2025 at 9:58 PM Andres Freund <[email protected]> wrote:
>
> Hi,
>
> On 2025-12-16 21:19:21 +0530, Dilip Kumar wrote:
> > Motivation
> > ========
> > 1) The check is performed frequently in the logical decoding path
> > (e.g., in pgoutput_change and pgoutput_truncate). Moving this to a
> > cached catalog attribute in pg_class allows for a simple check.
>
> You could solve this more resource-efficiently by putting the information in
> the relcache entry.
>
I feel the proposed solution (marking in pg_class) is required not
only to improve performance by avoiding OID checks in frequently
executed paths, but also to ensure consistent behavior when publishing
tables.
The existing approach does not provide a foolproof solution. As an
example, tables in information_schema are currently not eligible for
publication; but if information_schema is dropped and recreated, those
tables become eligible because their relid no longer falls under
FirstNormalObjectId (see steps in [1]). There may be other
existing/future scenarios with similar behavior. In my opinion, the
proposed solution is a good approach to ensure consistency in such
cases.
[1]:
****Pub****:
create publication pub1;
ALTER PUBLICATION pub1 ADD TABLE information_schema.sql_sizing;
select * from information_schema.sql_sizing where sizing_id=97;
****Sub****:
create subscription sub1 connection '...' publication pub1 with
(copy_data=false);
select * from information_schema.sql_sizing where sizing_id=97;
****Pub****:
alter table information_schema.sql_sizing replica identity full;
--this is not replicated.
UPDATE information_schema.sql_sizing set supported_value=12 where sizing_id=97;
****Sub****:
postgres=# select supported_value from information_schema.sql_sizing
where sizing_id=97;
supported_value
-----------------
0
~~
Then drop and recreate and try to perform the above update again, it
gets replicated:
drop schema information_schema cascade;
./psql -d postgres -f ./../../src/backend/catalog/information_schema.sql -p 5433
****Pub****:
ALTER PUBLICATION pub1 ADD TABLE information_schema.sql_sizing;
select * from information_schema.sql_sizing where sizing_id=97;
alter table information_schema.sql_sizing replica identity full;
--This is replicated
UPDATE information_schema.sql_sizing set supported_value=14 where sizing_id=97;
****Sub****:
--This shows supported_value as 14
postgres=# select supported_value from information_schema.sql_sizing
where sizing_id=97;
supported_value
-----------------
14
thanks
Shveta
