RE: repack: fix a bug to reject deferrable primary key fallback for concurrent mode

On Friday, April 17, 2026 11:35 AM Chao Li <li(dot)evan(dot)chao(at)gmail(dot)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.
>
> I tested this with the following procedure.
>
...
> With this patch, repack will quickly for the test:
> ```
> evantest=# repack (concurrently) t;
> ERROR: cannot process relation "t"
> HINT: Relation "t" has a deferrable primary key.
> ```

Good catch!

I think we can use the existing API to identify the index, for example:

diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c
index 67364cc60e3..cc30236f493 100644
--- a/src/backend/commands/repack.c
+++ b/src/backend/commands/repack.c
@@ -62,6 +62,7 @@
#include "miscadmin.h"
#include "optimizer/optimizer.h"
#include "pgstat.h"
+#include "replication/logicalrelation.h"
#include "storage/bufmgr.h"
#include "storage/lmgr.h"
#include "storage/predicate.h"
@@ -924,9 +925,7 @@ check_concurrent_repack_requirements(Relation rel, Oid *ident_idx_p)
* repack work with a FULL replica identity; however that requires more
* work and is not implemented yet.
*/
- ident_idx = RelationGetReplicaIndex(rel);
- if (!OidIsValid(ident_idx) && OidIsValid(rel->rd_pkindex))
- ident_idx = rel->rd_pkindex;
+ ident_idx = GetRelationIdentityOrPK();
if (!OidIsValid(ident_idx))
ereport(ERROR,
errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),

And it would be better to add a test for this.

Best Regards,
Hou zj