Re: Proposal: Conflict log history table for Logical Replication

On Wed, Jun 3, 2026 at 3:24 PM Nisha Moond <nisha(dot)moond412(at)gmail(dot)com> wrote:
>
> Thanks for the updated patches, please find my comments on the v44
> patches below. These appear to apply to v45-001 and v45-002 as well,
> as both are unchanged.
>

Here are couple more issues found during tests:

5) remote_commit_ts is available when streaming=on, in that case, we
are not updating it and hence see NULL in the CLT.
A simple test case:
-- publisher
ALTER SYSTEM SET logical_decoding_work_mem = '64kB';
SELECT pg_reload_conf();
CREATE TABLE t (a int PRIMARY KEY);
CREATE PUBLICATION pub FOR TABLE t;

-- subscriber (pre-insert the conflicting row, so copy_data=false)
CREATE TABLE t (a int PRIMARY KEY);
INSERT INTO t VALUES (1);
CREATE SUBSCRIPTION sub
CONNECTION 'host=localhost port=9933 dbname=postgres'
PUBLICATION pub WITH (conflict_log_destination = 'all', streaming
= on, copy_data = false);

Trigger a streaming conflict
-- publisher
BEGIN;
INSERT INTO t SELECT generate_series(2, 50000);
INSERT INTO t VALUES (1); -- conflicts with subscriber's existing row
COMMIT;

Check the CLT - remote_commit_ts is NULL despite timestamp being known
-- subscriber
SELECT conflict_type, remote_commit_ts, remote_commit_lsn
FROM pg_conflict.pg_conflict_log_<subid>;
conflict_type | remote_commit_ts | remote_commit_lsn
----------------+------------------+-------------------
insert_exists | | 0/1234ABC

I think we need to update it in apply_handle_stream_commit() -> case
TRANS_LEADER_APPLY:
remote_commit_ts = commit_data.committime;
~~~

6) Different ERRORs for superuser vs non-superuser
I created a subscription owned by a non-superuser (nisha), and the CLT
for it is:
postgres=# \d
List of relations
Schema | Name | Type | Owner
-------------+-----------------------+-------+---------
pg_conflict | pg_conflict_log_16469 | table | nisha

Now if I try to UPDATE the CLT as a superuser:

postgres=# update pg_conflict_log_16469 set conflict_type=
'INSERT_EXIST' where conflict_type='insert_exists';
ERROR: cannot modify or insert data into conflict log table
"pg_conflict_log_16469"
DETAIL: Conflict log tables are system-managed and only support
cleanup via DELETE or TRUNCATE.

However, running the same command as nisha (the sub/clt owner) results in:

postgres=# SET SESSION AUTHORIZATION nisha;
SET
postgres=> update pg_conflict_log_16469 set conflict_type=
'INSERT_EXIST' where conflict_type='insert_exists';
ERROR: permission denied for table pg_conflict_log_16469

I think the error should be consistent with the superuser case, rather
than failing with a generic permission error.

--
Thanks,
Nisha