v6-0001-ALTER-tbl-rewrite-loses-CLUSTER-ON-index.patch

diff --git a/src/backend/commands/tablecmds.c b/src/backend/commands/tablecmds.c
index 8c33b67c1b..73d9392878 100644
--- a/src/backend/commands/tablecmds.c
+++ b/src/backend/commands/tablecmds.c
@@ -177,6 +177,7 @@ typedef struct AlteredTableInfo
 	List	   *changedIndexOids;	/* OIDs of indexes to rebuild */
 	List	   *changedIndexDefs;	/* string definitions of same */
 	char	   *replicaIdentityIndex;	/* index to reset as REPLICA IDENTITY */
+	char	   *clusterOnIndex;		/* index to CLUSTER ON */
 } AlteredTableInfo;
 
 /* Struct describing one new constraint to check in Phase 3 scan */
@@ -11579,9 +11580,28 @@ RememberReplicaIdentityForRebuilding(Oid indoid, AlteredTableInfo *tab)
 	tab->replicaIdentityIndex = get_rel_name(indoid);
 }
 
+/*
+ * Subroutine for ATExecAlterColumnType: remember any clustered index.
+ */
+static void
+RememberClusterOnForRebuilding(Oid indoid, AlteredTableInfo *tab)
+{
+	if (!get_index_isclustered(indoid))
+		return;
+
+	if (tab->clusterOnIndex)
+		elog(ERROR, "relation %u has multiple clustered indexes", tab->relid);
+
+	tab->clusterOnIndex = get_rel_name(indoid);
+}
+
 /*
  * Subroutine for ATExecAlterColumnType: remember that a constraint needs
  * to be rebuilt (which we might already know).
+ *
+ * For constraint's index (if any), also remember if it's the table's replica
+ * identity or its clustered index, so that ATPostAlterTypeCleanup() can
+ * queue up commands necessary to restore that property.
  */
 static void
 RememberConstraintForRebuilding(Oid conoid, AlteredTableInfo *tab)
@@ -11604,9 +11624,18 @@ RememberConstraintForRebuilding(Oid conoid, AlteredTableInfo *tab)
 		tab->changedConstraintDefs = lappend(tab->changedConstraintDefs,
 											 defstring);
 
+		/*
+		 * For constraint's index (if any), remember if it's the table's
+		 * replica identity or its clustered index, so that
+		 * ATPostAlterTypeCleanup() can queue up commands necessary to restore
+		 * that property.
+		 */
 		indoid = get_constraint_index(conoid);
 		if (OidIsValid(indoid))
+		{
 			RememberReplicaIdentityForRebuilding(indoid, tab);
+			RememberClusterOnForRebuilding(indoid, tab);
+		}
 	}
 }
 
@@ -11650,7 +11679,13 @@ RememberIndexForRebuilding(Oid indoid, AlteredTableInfo *tab)
 			tab->changedIndexDefs = lappend(tab->changedIndexDefs,
 											defstring);
 
+			/*
+			 * Remember if it's the table's replica identity or its clustered
+			 * index, so that ATPostAlterTypeCleanup() can queue up commands
+			 * necessary to restore that property.
+			 */
 			RememberReplicaIdentityForRebuilding(indoid, tab);
+			RememberClusterOnForRebuilding(indoid, tab);
 		}
 	}
 }
@@ -11777,6 +11812,20 @@ ATPostAlterTypeCleanup(List **wqueue, AlteredTableInfo *tab, LOCKMODE lockmode)
 			lappend(tab->subcmds[AT_PASS_OLD_CONSTR], cmd);
 	}
 
+	/*
+	 * Queue up command to restore clustered index marking
+	 */
+	if (tab->clusterOnIndex)
+	{
+		AlterTableCmd *cmd = makeNode(AlterTableCmd);
+
+		cmd->subtype = AT_ClusterOn;
+		cmd->name = tab->clusterOnIndex;
+
+		/* do it after indexes and constraints */
+		tab->subcmds[AT_PASS_OLD_CONSTR] =
+			lappend(tab->subcmds[AT_PASS_OLD_CONSTR], cmd);
+	}
 	/*
 	 * It should be okay to use DROP_RESTRICT here, since nothing else should
 	 * be depending on these objects.
diff --git a/src/backend/utils/cache/lsyscache.c b/src/backend/utils/cache/lsyscache.c
index 27bbb58f56..9c5b806c22 100644
--- a/src/backend/utils/cache/lsyscache.c
+++ b/src/backend/utils/cache/lsyscache.c
@@ -3299,3 +3299,26 @@ get_index_isvalid(Oid index_oid)
 
 	return isvalid;
 }
+
+/*
+ * get_index_isclustered
+ *
+ *		Given the index OID, return pg_index.indisclustered.
+ */
+bool
+get_index_isclustered(Oid index_oid)
+{
+	bool		isclustered;
+	HeapTuple	tuple;
+	Form_pg_index rd_index;
+
+	tuple = SearchSysCache1(INDEXRELID, ObjectIdGetDatum(index_oid));
+	if (!HeapTupleIsValid(tuple))
+		elog(ERROR, "cache lookup failed for index %u", index_oid);
+
+	rd_index = (Form_pg_index) GETSTRUCT(tuple);
+	isclustered = rd_index->indisclustered;
+	ReleaseSysCache(tuple);
+
+	return isclustered;
+}
diff --git a/src/include/utils/lsyscache.h b/src/include/utils/lsyscache.h
index 4e646c55e9..9459c6a94f 100644
--- a/src/include/utils/lsyscache.h
+++ b/src/include/utils/lsyscache.h
@@ -184,6 +184,7 @@ extern Oid	get_range_collation(Oid rangeOid);
 extern Oid	get_index_column_opclass(Oid index_oid, int attno);
 extern bool	get_index_isreplident(Oid index_oid);
 extern bool get_index_isvalid(Oid index_oid);
+extern bool get_index_isclustered(Oid index_oid);
 
 #define type_is_array(typid)  (get_element_type(typid) != InvalidOid)
 /* type_is_array_domain accepts both plain arrays and domains over arrays */
diff --git a/src/test/regress/expected/alter_table.out b/src/test/regress/expected/alter_table.out
index fb6d86a269..a01c6d6ec5 100644
--- a/src/test/regress/expected/alter_table.out
+++ b/src/test/regress/expected/alter_table.out
@@ -4296,3 +4296,37 @@ create trigger xtrig
 update bar1 set a = a + 1;
 INFO:  a=1, b=1
 /* End test case for bug #16242 */
+-- alter type rewrite/rebuild should preserve cluster marking on index
+create table alttype_cluster (a int);
+create index alttype_cluster_a on alttype_cluster (a);
+alter table alttype_cluster cluster on alttype_cluster_a;
+select indisclustered from pg_index where indrelid = 'alttype_cluster'::regclass;
+ indisclustered 
+----------------
+ t
+(1 row)
+
+alter table alttype_cluster alter a type bigint;
+select indisclustered from pg_index where indrelid = 'alttype_cluster'::regclass;
+ indisclustered 
+----------------
+ t
+(1 row)
+
+drop index alttype_cluster_a;
+alter table alttype_cluster add primary key (a);
+alter table alttype_cluster cluster on alttype_cluster_pkey;
+select indisclustered from pg_index where indrelid = 'alttype_cluster'::regclass;
+ indisclustered 
+----------------
+ t
+(1 row)
+
+alter table alttype_cluster alter a type int;
+select indisclustered from pg_index where indrelid = 'alttype_cluster'::regclass;
+ indisclustered 
+----------------
+ t
+(1 row)
+
+drop table alttype_cluster;
diff --git a/src/test/regress/sql/alter_table.sql b/src/test/regress/sql/alter_table.sql
index 3801f19c58..4eeec24e58 100644
--- a/src/test/regress/sql/alter_table.sql
+++ b/src/test/regress/sql/alter_table.sql
@@ -2840,3 +2840,18 @@ create trigger xtrig
 update bar1 set a = a + 1;
 
 /* End test case for bug #16242 */
+
+-- alter type rewrite/rebuild should preserve cluster marking on index
+create table alttype_cluster (a int);
+create index alttype_cluster_a on alttype_cluster (a);
+alter table alttype_cluster cluster on alttype_cluster_a;
+select indisclustered from pg_index where indrelid = 'alttype_cluster'::regclass;
+alter table alttype_cluster alter a type bigint;
+select indisclustered from pg_index where indrelid = 'alttype_cluster'::regclass;
+drop index alttype_cluster_a;
+alter table alttype_cluster add primary key (a);
+alter table alttype_cluster cluster on alttype_cluster_pkey;
+select indisclustered from pg_index where indrelid = 'alttype_cluster'::regclass;
+alter table alttype_cluster alter a type int;
+select indisclustered from pg_index where indrelid = 'alttype_cluster'::regclass;
+drop table alttype_cluster;