Re: Proposal: Conflict log history table for Logical Replication

On Thu, 2 Jul 2026 at 13:39, Dilip Kumar <dilipbalaut(at)gmail(dot)com> wrote:
>
> On Wed, Jul 1, 2026 at 6:55 PM Dilip Kumar <dilipbalaut(at)gmail(dot)com> wrote:
> >
> > On Wed, Jul 1, 2026 at 1:16 PM shveta malik <shveta(dot)malik(at)gmail(dot)com> wrote:
> > >
> > > On Wed, Jul 1, 2026 at 12:45 PM Dilip Kumar <dilipbalaut(at)gmail(dot)com> wrote:
> > > >
> > > > Thanks I have fixed these comments and also merged the docs.
> > >
> > > Thanks. Sharing the version with pgindent run on v61.
> >
> > Here is the updated patch version. It fixes offlist review comments
> > provided by Amit and Shveta, bumps the catversion and adds authors and
> > reviewers details.
>
> I rebased the remaining patches on top of HEAD. So far, I have run
> pgindent and completed the doc merge for 0001. The 0002 and 0003 are
> just rebased.

Hi Dilip,

While testing I hit the following assert:
+ if (OidIsValid(relid))
+ {
+ /* Existing table from upgrade */
+ Assert(IsBinaryUpgrade);
+ }

Steps to reproduce:
1. Suppose initially we have a logical replication setup and the
subscriber is created with 'conflict_log_destination = log'
2. Now we have two psql sessions of the subscriber node. Attach GDB to
first session and add breakpoint to line:
AlterSubscription->LockSharedObject(SubscriptionRelationId, subid, 0,
AccessExclusiveLock);
3.Execute 'ALTER SUBSCRIPTION sub1 SET (conflict_log_destination =
'all')' on the first session. It will stop at the breakpoint.
4. Now execute 'ALTER SUBSCRIPTION sub1 SET (conflict_log_destination
= 'all');' on the second session. The execution on the second session
is successful and a conflict log table is created.
5. Continue the execution of the first session. This will hit the
above Assert condition.

I think this happens because for the first session, we have the stale
copy of 'sub'.
While the first session is stopped at the breakpoint, the second
session successfully executes ALTER SUBSCRIPTION and creates the
conflict log table. When the first session resumes, it still sees the
old value of old_dest (i.e CONFLICT_LOG_DEST_LOG), so
'opts.conflictlogdest != old_dest' evaluates to true and
'alter_sub_conflict_log_dest()' is invoked.
Since the second session has already created the conflict log table
and 'want_table' is true, the code finds an existing conflict log
table '(OidIsValid(relid))', causing the assert to fire.

Thanks,
Shlok Kyal