Re: Proposal: Conflict log history table for Logical Replication

On Fri, Jun 26, 2026 at 11:25 AM vignesh C <vignesh21@gmail.com> wrote:
>
> On Thu, 25 Jun 2026 at 19:15, Dilip Kumar <dilipbalaut@gmail.com> wrote:
> >
> > PFA, updated version of the patch, fixes all the comments of V57
>
> Currently, I have a use case where I would like to clean up conflict
> log records using a 'MERGE' statement.
>
> Consider a system that has accumulated conflict records over several
> days or weeks. Some of those conflicts have already been resolved, and
> in the meantime, a number of tables have been removed from the
> publication, dropped on the subscriber, or are otherwise no longer
> part of logical replication. However, the corresponding conflict log
> records remain in the conflict log table.
>
> One way to clean up such stale entries is to compare the 'relid'
> stored in the conflict log table with 'pg_class' and delete rows whose
> relations no longer exist. For example:
> MERGE INTO pg_conflict.pg_conflict_log_16404 AS cl
> USING pg_class AS c
> ON (cl.relid = c.oid)
> WHEN NOT MATCHED BY SOURCE THEN
>     DELETE;
> However, this fails with:
> ERROR:  cannot modify or insert data into conflict log table
> "pg_conflict_log_16404"
> DETAIL:  Conflict log tables are system-managed and only support
> cleanup using DELETE or TRUNCATE.
>
> Although this 'MERGE' only performs a 'DELETE', it is still rejected.
>
> Is this restriction intentional? I can understand if supporting
> 'MERGE' is considered out of scope for this patch, but I wanted to
> check whether rejecting a delete-only 'MERGE' is an intentional design
> decision. If so, perhaps support for this use case could be considered
> in a future version.
>

Yes, in future versions, we may want to consider such cases. BTW,
can't we achieve this simply via DELETE?

-- 
With Regards,
Amit Kapila.