Re: Proposal: Conflict log history table for Logical Replication

On Wed, Jan 7, 2026 at 12:12 PM shveta malik <shveta.malik@gmail.com> wrote:
>
> Hi Dilip,
> Please find a few comments on v19-001:
>
> 1)
> We can replace IsConflictLogTable(relid)  with
> IsConflictClass(reltuple). Wherever we call IsConflictLogTable(), we
> have already fetched reltuple from pg_class for that relid, we can
> simply use that to see if it belongs to pg_conflict namespace. That
> will avoid the need of
> patch004 as well to 'Introduce a dedicated shared unique index on
> pg_subscription.subconflictlogrelid'.
>
> 2)
> + if (opts.logdest == CONFLICT_LOG_DEST_TABLE ||
> + opts.logdest == CONFLICT_LOG_DEST_ALL)
>
> We can replace with:
>
> IsSet(opts.logdest, CONFLICT_LOG_DEST_TABLE);
>
> 3)
> +-- this should generate an internal table named pg_conflict_$subid$
> +CREATE SUBSCRIPTION regress_conflict_test1 CONNECTION
> 'dbname=regress_doesnotexist' PUBLICATION testpub WITH (connect =
> false, conflict_log_destination = 'table');
> +
>
> I think we shall verify 2 things here:
> a) Table is created in pg_conflict namespace.
> b) Table has name pg_conflict_<subid>
>
> 4)
> We can add these 3 simple tests as well:
> a) Trying to alter and truncate pg_conflict_subid table.
> b) Trying to create a new table in pg_conflict namespace.
> c) Moving a table into pg_conflict namespace.
>
> ~~
>
> Overall, I’m concerned about how users will manage this table as it
> grows. There is currently no way to purge old data, truncation is
> disallowed, and the table must be sub-ID–tied, which also prevents
> users from attaching a different table as a CLT (if needed).
> Additionally, we do not offer any form of partitioning.
> Do you think we should provide users with a basic purge mechanism? At
> the very least, should we allow truncation so users can take a backup
> and truncate a sub-ID–tied CLT to start afresh? Thoughts?

Yeah that's a valid concern, there should be some way to purge data
from this table, I think we can allow truncate/delete on this table,
currently I haven't blocked the DML operations on that table and
similarly we can allow truncate as well.

-- 
Regards,
Dilip Kumar
Google