Subject: [PATCH] Copy the relevant pg_attrdef catalog entries for the transient relation.

From: Antonin Houska <[email-masked]>
Date: Mon, 22 Jun 2026 09:34:05 +0200

The default values may be needed by the executor when processing the
concurrent data changes. In particular, ExecInsertIndexTuples() needs it when
determining the value of the 'indexUnchanged' hint for the index AM.

Like in copy_index_constraints(), we make the new catalog entries dependent on
the transient relation, so they are dropped along with it automatically.
---
 src/backend/commands/repack.c                 | 97 +++++++++++++++++++
 .../injection_points/specs/repack.spec        |  3 +-
 2 files changed, 99 insertions(+), 1 deletion(-)

diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c
index 4d177c868bb..725efa236bc 100644
--- a/src/backend/commands/repack.c
+++ b/src/backend/commands/repack.c
@@ -48,6 +48,7 @@
 #include "catalog/namespace.h"
 #include "catalog/objectaccess.h"
 #include "catalog/pg_am.h"
+#include "catalog/pg_attrdef.h"
 #include "catalog/pg_constraint.h"
 #include "catalog/pg_inherits.h"
 #include "catalog/toasting.h"
@@ -204,6 +205,7 @@ static void rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHea
 static List *build_new_indexes(Relation NewHeap, Relation OldHeap, List *OldIndexes);
 static void copy_index_constraints(Relation old_index, Oid new_index_id,
 								   Oid new_heap_id);
+static void copy_attribute_defaults(Relation old_heap, Relation new_heap);
 static Relation process_single_relation(RepackStmt *stmt,
 										LOCKMODE lockmode,
 										bool isTopLevel,
@@ -1083,6 +1085,13 @@ rebuild_relation(Relation OldHeap, Relation index, bool verbose,
 	Assert(CheckRelationOidLockedByMe(OIDNewHeap, AccessExclusiveLock, false));
 	NewHeap = table_open(OIDNewHeap, NoLock);
 
+	/*
+	 * Copy attribute defaults - the executor may need them, in order to
+	 * process the concurrent data changes. In particular, this is related to
+	 * ExecInsertIndexTuples().
+	 */
+	copy_attribute_defaults(OldHeap, NewHeap);
+
 	/* Copy the heap data into the new table in the desired order */
 	copy_table_data(NewHeap, OldHeap, index, snapshot, verbose,
 					&swap_toast_by_content, &frozenXid, &cutoffMulti);
@@ -3434,6 +3443,94 @@ copy_index_constraints(Relation old_index, Oid new_index_id, Oid new_heap_id)
 	CommandCounterIncrement();
 }
 
+/*
+ * Create a transient copy of attribute defaults for the transient table.
+ *
+ * Like above, the executor needs information on attribute defaults. Once the
+ * repacking is finished, the catalog entries we create here are dropped.
+ */
+static void
+copy_attribute_defaults(Relation old_heap, Relation new_heap)
+{
+	Oid		old_heap_id = RelationGetRelid(old_heap);
+	Oid		new_heap_id = RelationGetRelid(new_heap);
+	ScanKeyData skey;
+	Relation	rel;
+	Relation	att_rel = NULL;
+	TupleDesc	desc;
+	SysScanDesc scan;
+	HeapTuple	tup;
+	ObjectAddress objrel;
+
+	rel = table_open(AttrDefaultRelationId, RowExclusiveLock);
+	ObjectAddressSet(objrel, RelationRelationId, new_heap_id);
+
+	ScanKeyInit(&skey,
+				Anum_pg_attrdef_adrelid,
+				BTEqualStrategyNumber, F_OIDEQ,
+				ObjectIdGetDatum(old_heap_id));
+	scan = systable_beginscan(rel, AttrDefaultIndexId, true,
+							  NULL, 1, &skey);
+	desc = RelationGetDescr(rel);
+	while (HeapTupleIsValid(tup = systable_getnext(scan)))
+	{
+		Form_pg_attrdef	adform;
+		Oid			oid;
+		Datum		values[Natts_pg_attrdef] = {0};
+		bool		nulls[Natts_pg_attrdef] = {0};
+		bool		replaces[Natts_pg_attrdef] = {0};
+		HeapTuple	new_tup, att_tup, att_new_tup;
+		ObjectAddress objad;
+		Datum		att_values[Natts_pg_attribute] = {0};
+		bool		att_nulls[Natts_pg_attribute] = {0};
+		bool		att_replaces[Natts_pg_attribute] = {0};
+
+		adform = (Form_pg_attrdef) GETSTRUCT(tup);
+		Assert(adform->adrelid == old_heap_id);
+
+		oid = GetNewOidWithIndex(rel, AttrDefaultOidIndexId,
+								 Anum_pg_attrdef_oid);
+		values[Anum_pg_attrdef_oid - 1] = ObjectIdGetDatum(oid);
+		replaces[Anum_pg_attrdef_oid - 1] = true;
+		values[Anum_pg_attrdef_adrelid - 1] = ObjectIdGetDatum(new_heap_id);
+		replaces[Anum_pg_attrdef_adrelid - 1] = true;
+
+		new_tup = heap_modify_tuple(tup, desc, values, nulls, replaces);
+
+		/* Insert it into the catalog. */
+		CatalogTupleInsert(rel, new_tup);
+
+		/* Create a dependency so it's removed when we drop the new heap. */
+		ObjectAddressSet(objad, AttrDefaultRelationId, oid);
+		recordDependencyOn(&objad, &objrel, DEPENDENCY_AUTO);
+
+		/* Set atthasdef - new heap has it cleared. */
+		att_tup = SearchSysCache2(ATTNUM,
+							ObjectIdGetDatum(new_heap_id),
+							ObjectIdGetDatum(adform->adnum));
+		if (!HeapTupleIsValid(att_tup))
+			elog(ERROR, "cache lookup failed for attribute %d of relation %u",
+				 adform->adnum, new_heap_id);
+
+		att_values[Anum_pg_attribute_atthasdef - 1] = BoolGetDatum(true);
+		att_replaces[Anum_pg_attribute_atthasdef - 1] = true;
+
+		if (att_rel == NULL)
+			att_rel = table_open(AttributeRelationId, RowExclusiveLock);
+		att_new_tup = heap_modify_tuple(att_tup, RelationGetDescr(att_rel),
+										att_values, att_nulls, att_replaces);
+		ReleaseSysCache(att_tup);
+		CatalogTupleUpdate(att_rel, &att_new_tup->t_self, att_new_tup);
+	}
+	systable_endscan(scan);
+
+	table_close(rel, RowExclusiveLock);
+	if (att_rel)
+		table_close(att_rel, RowExclusiveLock);
+
+	CommandCounterIncrement();
+}
+
 /*
  * Try to start a background worker to perform logical decoding of data
  * changes applied to relation while REPACK CONCURRENTLY is copying its
diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec
index d727a9b056b..7896d1456ad 100644
--- a/src/test/modules/injection_points/specs/repack.spec
+++ b/src/test/modules/injection_points/specs/repack.spec
@@ -3,7 +3,8 @@ setup
 {
 	CREATE EXTENSION injection_points;
 
-	CREATE TABLE repack_test(i int PRIMARY KEY, j int);
+	CREATE TABLE repack_test(i int PRIMARY KEY, j int,
+				 k int GENERATED ALWAYS AS (j * 2) STORED);
 	INSERT INTO repack_test(i, j) VALUES (1, 1), (2, 2), (3, 3), (4, 4);
 
 	CREATE TABLE relfilenodes(node oid);
-- 
2.52.0

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