Re: Proposal: Conflict log history table for Logical Replication - Mailing list pgsql-hackers

On Wed, May 6, 2026 at 7:34 PM Dilip Kumar <dilipbalaut@gmail.com> wrote:
>
> On Wed, May 6, 2026 at 6:28 PM Dilip Kumar <dilipbalaut@gmail.com> wrote:
> >
> > On Wed, May 6, 2026 at 4:31 PM Amit Kapila <amit.kapila16@gmail.com> wrote:
> > >
> > > On Wed, May 6, 2026 at 3:01 PM shveta malik <shveta.malik@gmail.com> wrote:
> > > >
> > > > On Wed, May 6, 2026 at 9:24 AM vignesh C <vignesh21@gmail.com> wrote:
> > > > >
> > > > > Few comments:
> > > > > 1) Currently we allow renaming of pg_conflict schema, this might be ok
> > > > > as we allow other sysem schema like pg_catalog and pg_toast also.
> > > > > postgres=# alter schema pg_conflict rename to test_conflict;
> > > > > ALTER SCHEMA
> > > > >
> > > >
> > > > I agree that we allow renaming other schemas including pg_toast, but I
> > > > am not sure if this is consciously made decision, see BUG #18281 ast
> > > > [1]. I don't favour allowing renaming pg_conflict for 2 reasons:
> > > >
> > > > 1) Because Postgres explicitly blocks renaming schemas to a name
> > > > starting with 'pg_'. If an admin accidentally renames 'pg_conflict' to
> > > > something else, they are permanently locked out from renaming it back.
> > > >
> > > > 2) While the core worker might survive a rename via OID lookups;
> > > > external scripts, extensions, and monitoring tools will likely
> > > > hardcode the 'pg_conflict' string. If the schema is renamed, these
> > > > tools will fail.
> > > >
> > >
> > > I think we shouldn't go out of our way to disallow superusers to
> > > rename pg_conflict schema similar to other cases. We can try to
> > > prevent hard-coding schema names where possible but not sure we can
> > > guarantee that nothing related to pg_conflict schema won't break as
> > > shown by you in the following similar case for pg_conflict.
> > >
> > > > One such example  of scripts breaking is present event in Postgres. I
> > > > did the following, and most of psql commands started failing after
> > > > that due to hard-coded pg_catalog name in them.
> > > >
> > > > postgres=# alter schema pg_catalog rename to catalog_new;
> > > > ALTER SCHEMA
> > > >
> > > > postgres=# \d catalog_new.*
> > > > ERROR:  relation "pg_catalog.pg_class" does not exist
> > > > LINE 5: FROM pg_catalog.pg_class c
> > > >
> > > > [1]: https://www.postgresql.org/message-id/flat/18281-5b1b6c5991d345aa%40postgresql.org
> >
> > I can see pg_toast and pg_catalog schema also hard coded in couple of
> > places e.g.
> >
> > listPartitionedTables()
> > {
> > if (!pattern)
> > appendPQExpBufferStr(&buf, " AND n.nspname <> 'pg_catalog'\n"
> > " AND n.nspname !~ '^pg_toast'\n"
> > " AND n.nspname <> 'information_schema'\n");
> > }
> >
> > I will analyze which all places we are hardcoding, I think on server
> > side code we can easily avoid but from client side e.g. describe we
> > might need to invent a way to identify the schema name, or we might
> > have to store it somewhere in pg_subscription etc, I don't think we
> > should go that route.
>
> Here is updated patch set
>
> Open comments:
> 1. Analyze and avoid hardcoding the 'pg_conflict' schema name wherever possible
> 2. change the way we display clt in \dRs+
> 3. Transfer the clt ownership when subscription ownership has change
> (Note: I have coded a poc for this but still checking whether it works
> in all cases)
>
> I will send the revised version by end of this week after fixing these
> open comments as well.

So for the ownership change, this simple change[1] is working fine,
but there is another issue that currently we can assign subscription
nownership to any user even that doesn't have pg_create_subscription
maybe that should be fine as it is not creating the subscription but
now question is how to manage the permission on the conflict log table
see below test[2]


[1[]
diff --git a/src/backend/commands/subscriptioncmds.c
b/src/backend/commands/subscriptioncmds.c
index a2de57e17b4..c9fac56714e 100644
--- a/src/backend/commands/subscriptioncmds.c
+++ b/src/backend/commands/subscriptioncmds.c
@@ -2718,6 +2718,10 @@ AlterSubscriptionOwner_internal(Relation rel,
HeapTuple tup, Oid newOwnerId)
        form->subowner = newOwnerId;
        CatalogTupleUpdate(rel, &tup->t_self, tup);
+       /* Update owner of the conflict log table if it exists */
+       if (OidIsValid(form->subconflictlogrelid))
+               ATExecChangeOwner(form->subconflictlogrelid,
newOwnerId, true, AccessExclusiveLock);
+
        /* Update owner dependency reference */
        changeDependencyOnOwner(SubscriptionRelationId,
                                                        form->oid,

[2]
-- test to show the ownership is getting changed for the table, but
now this user will have access issue on the pg_conflict_log table as
this user do not have pg_create_subscription role, I haven't yet
checked whether the problems are only related to clt access or there
would be issue for other subcription management as well.

postgres[557253]=# SELECT relname, relowner FROM pg_class WHERE
relname = 'pg_conflict_log_16406';
        relname        | relowner
-----------------------+----------
 pg_conflict_log_16406 |       10
(1 row)

postgres[557253]=# CREATE USER test;
CREATE ROLE
postgres[557253]=# ALTER SUBSCRIPTION sub OWNER TO test;
ALTER SUBSCRIPTION
postgres[557253]=# SELECT relname, relowner FROM pg_class WHERE
relname = 'pg_conflict_log_16406';
        relname        | relowner
-----------------------+----------
 pg_conflict_log_16406 |    16410
(1 row)


--
Regards,
Dilip Kumar
Google