Re: Proposal: Conflict log history table for Logical Replication

On Thu, Nov 27, 2025 at 5:50 PM Dilip Kumar <dilipbalaut(at)gmail(dot)com> wrote:
>
>
> I have fixed all these comments and also the comments of 0002, now I
> feel we can actually merge 0001 and 0002, so I have merged both of
> them.
>
> Now pending work status
> 1) fixed review comments of 0003
> 2) Run pgindent -- planning to do it after we complete the first level
> of review
> 3) Subscription TAP test for logging the actual conflicts
>

Thanks for the patch. A few observations:

1)
It seems, as per LOG, 'key' and 'replica-identity' are different when
it comes to insert_exists, update_exists and
multiple_unique_conflicts, while I believe in CLT, key is
replica-identity i.e. there are no 2 separate terms. Please see below:

a)
Update_Exists:
2025-11-28 14:08:56.179 IST [60383] ERROR: conflict detected on
relation "public.tab1": conflict=update_exists
2025-11-28 14:08:56.179 IST [60383] DETAIL: Key already exists in
unique index "tab1_pkey", modified locally in transaction 790 at
2025-11-28 14:07:17.578887+05:30.
Key (i)=(40); existing local row (40, 10); remote row (40, 200);
replica identity (i)=(20).

postgres=# select conflict_type, key_tuple,local_tuple,remote_tuple
from clt where conflict_type='update_exists';
conflict_type | key_tuple | local_tuple | remote_tuple
---------------+-----------+-----------------+------------------
update_exists | {"i":20} | {"i":40,"j":10} | {"i":40,"j":200}

b)
insert_Exists:
ERROR: conflict detected on relation "public.tab1": conflict=insert_exists
DETAIL: Key already exists in unique index "tab1_pkey", modified
locally in transaction 767 at 2025-11-28 13:59:22.431097+05:30.
Key (i)=(30); existing local row (30, 10); remote row (30, 10).

postgres=# select conflict_type, key_tuple,local_tuple,remote_tuple from clt;
conflict_type | key_tuple | local_tuple | remote_tuple
----------------+-----------+-----------------+-----------------
insert_exists | | {"i":30,"j":10} | {"i":30,"j":10}

case a) has key_tuple same as replica-identity of LOG
case b) does not have replica-identity and thus key_tuple is NULL.

Does that mean we need to maintain both key_tuple and RI separately in
CLT? Thoughts?

2)
For multiple_unique_conflict (testcase is same as I shared earlier),
it asserts here:
CONTEXT: processing remote data for replication origin "pg_16390"
during message type "INSERT" for replication target relation
"public.conf_tab" in transaction 778, finished at 0/017E6DE8
TRAP: failed Assert("MyLogicalRepWorker->conflict_log_tuple == NULL"),
File: "conflict.c", Line: 749, PID: 60627

I have not checked it, but maybe
'MyLogicalRepWorker->conflict_log_tuple' is left over from the
previous few tests I tried?

thanks
Shveta