From: Antonin Houska <ah@cybertec.at>
To: Chao Li <li.evan.chao@gmail.com>
cc: PostgreSQL-development <pgsql-hackers@postgresql.org>
Subject: Re: repack: fix a bug to reject deferrable primary key fallback for
 concurrent mode
In-reply-to: <10DD5E13-B45D-44F1-BE08-C63E00ABCAC0@gmail.com>
References: <10DD5E13-B45D-44F1-BE08-C63E00ABCAC0@gmail.com>
Comments: In-reply-to Chao Li <li.evan.chao@gmail.com>
   message dated "Fri, 17 Apr 2026 11:35:14 +0800."
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Date: Mon, 20 Apr 2026 16:52:15 +0200
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Chao Li <li.evan.chao@gmail.com> wrote:

> I am continuing to test REPACK, and I found another issue.
> 
> In check_concurrent_repack_requirements(), if a table has no replica identity index, the code falls back to using the primary key if one exists. The problem is that a deferrable primary key cannot be used for this purpose. WAL generation does not consider a deferrable primary key to be a replica identity, so concurrent mode may not receive enough old tuple information to replay concurrent changes.

Thanks for finding it, this is certainly a problem.

I'm just thinking if it's worth a separate error message.
RelationGetIndexList() just ignores the deferrable PK

	if (replident == REPLICA_IDENTITY_DEFAULT && OidIsValid(pkeyIndex) && !pkdeferrable)
		relation->rd_replidindex = pkeyIndex;

and if there's no other suitable index, the result is that there is no
identity index for the table. So the change attached here should be consistent
with this approach.

-- 
Antonin Houska
Web: https://www.cybertec-postgresql.com


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diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c
index 67364cc60e3..8cfc3fde5c7 100644
--- a/src/backend/commands/repack.c
+++ b/src/backend/commands/repack.c
@@ -925,7 +925,8 @@ check_concurrent_repack_requirements(Relation rel, Oid *ident_idx_p)
 	 * work and is not implemented yet.
 	 */
 	ident_idx = RelationGetReplicaIndex(rel);
-	if (!OidIsValid(ident_idx) && OidIsValid(rel->rd_pkindex))
+	if (!OidIsValid(ident_idx) && OidIsValid(rel->rd_pkindex) &&
+		!rel->rd_ispkdeferrable)
 		ident_idx = rel->rd_pkindex;
 	if (!OidIsValid(ident_idx))
 		ereport(ERROR,

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