Re: Proposal: Conflict log history table for Logical Replication

On Mon, 24 Aug 2026 at 21:01, Dilip Kumar <dilipbalaut(at)gmail(dot)com> wrote:
>
> Yes this makes sense. Here is the new version of patches which usage
> v71_1-0001 as base patch and v71-0002 is rebased on top of that and
> the the ommitting the large column patch is implemented as a top up
> patch

Incorrect replica_identity_full value in conflict log table. There
appears to be an issue in insert_conflict_log_tuple() when determining
the representation of the local replica identity. The current
implementation uses GetRelationIdentityOrPK() to distinguish REPLICA
IDENTITY FULL from an index-based replica identity:
+ Oid replica_index =
GetRelationIdentityOrPK(rel);
+
+ /*
+ * If the table has a valid replica identity index,
build the index
+ * JSON datum from key value. Otherwise, construct it from the
+ * complete tuple in REPLICA IDENTITY FULL cases.
+ */
+ if (OidIsValid(replica_index))
+ {
+ values[attno++] = BoolGetDatum(false);
+ values[attno++] =
tuple_table_slot_to_indextup_json(estate, rel,
+

replica_index,
+
searchslot);
+ }
+ else
+ {
+ values[attno++] = BoolGetDatum(true);
+ values[attno++] =
tuple_table_slot_to_json_datum(searchslot);
+ }

The problem is that GetRelationIdentityOrPK() returns InvalidOid for
three different replica identity states, not only for REPLICA IDENTITY
FULL:
relreplident = 'f' — REPLICA IDENTITY FULL
relreplident = 'n' — REPLICA IDENTITY NOTHING
relreplident = 'd' — REPLICA IDENTITY DEFAULT with no primary key

As a result, all three cases enter the else branch and
replica_identity_full is set to true. Thus, the replica_identity_full
column does not actually indicate whether the relation is configured
with REPLICA IDENTITY FULL; it instead indicates that
GetRelationIdentityOrPK() did not find a replica identity index.

This can be reproduced with the following test:
Publisher
CREATE TABLE tab_full (a int, b text);
ALTER TABLE tab_full REPLICA IDENTITY FULL;
CREATE TABLE tab_nothing (a int, b text);
ALTER TABLE tab_nothing REPLICA IDENTITY NOTHING;
CREATE TABLE tab_nopk (a int, b text);
CREATE TABLE tab_pk (a int PRIMARY KEY, b text);
INSERT INTO tab_full VALUES (1, 'from publisher');
INSERT INTO tab_nothing VALUES (1, 'from publisher');
INSERT INTO tab_nopk VALUES (1, 'from publisher');
INSERT INTO tab_pk VALUES (1, 'from publisher');
CREATE PUBLICATION pub FOR ALL TABLES;

Subscriber
CREATE TABLE tab_full (a int, b text);
ALTER TABLE tab_full REPLICA IDENTITY FULL;
CREATE TABLE tab_nothing (a int, b text);
ALTER TABLE tab_nothing REPLICA IDENTITY NOTHING;
CREATE TABLE tab_nopk (a int, b text);
CREATE TABLE tab_pk (a int PRIMARY KEY, b text);
CREATE SUBSCRIPTION ... PUBLICATION pub;

Generate a local origin on the subscriber:
UPDATE tab_full SET b = b;
UPDATE tab_nothing SET b = b;
UPDATE tab_nopk SET b = b;
UPDATE tab_pk SET b = b;

Then generate conflicts from the publisher:
UPDATE tab_full SET b = 'from subscriber conflict';
UPDATE tab_nothing SET b = 'from subscriber conflict';
UPDATE tab_nopk SET b = 'from subscriber conflict';
UPDATE tab_pk SET b = 'from subscriber conflict';

The local replica identity configuration is:
SELECT relname, relreplident FROM pg_class WHERE relname IN
('tab_full', 'tab_nothing', 'tab_nopk', 'tab_pk');
relname | relreplident
-------------+--------------
tab_full | f
tab_nothing | n
tab_nopk | d
tab_pk | d
(4 rows)

However, the conflict log records:
select relname, replica_identity_full from pg_conflict.pg_conflict_log_16395;
relname | replica_identity_full
-------------+-----------------------
tab_full | t
tab_nothing | t
tab_nopk | t
tab_pk | f
(4 rows)

The tab_nothing and tab_nopk entries demonstrate the issue: although
their local replica identities are NOTHING and DEFAULT respectively,
both are reported with replica_identity_full = true.

I think the code should explicitly check relreplident (or otherwise
distinguish REPLICA IDENTITY FULL from the other cases) rather than
using InvalidOid from GetRelationIdentityOrPK() as an indication of
REPLICA IDENTITY FULL. In particular, replica_identity_full should be
true only when the local relation actually has REPLICA IDENTITY FULL.

Additionally, should we update documentation for REPLICA IDENTITY
NOTHING and DEFAULT here?
+ <row>
+ <entry><literal>replica_identity_full</literal></entry>
+ <entry><type>boolean</type></entry>
+ <entry>Indicates whether <literal>replica_identity</literal>
represents a full tuple (<literal>true</literal>) or key values of a
replica identity index (<literal>false</literal>). This is
<literal>NULL</literal> when <literal>replica_identity</literal> is
not logged.</entry>
+ </row>

Regards,
Vignesh