Re: Proposal: Conflict log history table for Logical Replication

On Sun, Dec 14, 2025 at 9:16 PM Dilip Kumar <dilipbalaut@gmail.com> wrote:
>
> Here is the patch which implements the dependency and fixes other
> comments from Shveta.
>

+/*
+ * Check if the specified relation is used as a conflict log table by any
+ * subscription.
+ */
+bool
+IsConflictLogTable(Oid relid)
+{
+ Relation rel;
+ TableScanDesc scan;
+ HeapTuple tup;
+ bool is_clt = false;
+
+ rel = table_open(SubscriptionRelationId, AccessShareLock);
+ scan = table_beginscan_catalog(rel, 0, NULL);
+
+ while (HeapTupleIsValid(tup = heap_getnext(scan, ForwardScanDirection)))

This function has been used at multiple places in the patch, though
not in any performance-critical paths, but still, it seems like the
impact can be noticeable for a large number of subscriptions. Also, I
am not sure it is a good design to scan the entire system table to
find whether some other relation is publishable or not. I see below
kinds of usages for it:

+ /* Subscription conflict log tables are not published */
+ result = is_publishable_class(relid, (Form_pg_class) GETSTRUCT(tuple)) &&
+ !IsConflictLogTable(relid);

In this regard, I see a comment atop is_publishable_class which
suggests as follows:

The best
 * long-term solution may be to add a "relispublishable" bool to pg_class,
 * and depend on that instead of OID checks.
 */
static bool
is_publishable_class(Oid relid, Form_pg_class reltuple)

I feel that is a good idea for reasons mentioned atop
is_publishable_class and for the conflict table. What do you think?

-- 
With Regards,
Amit Kapila.