Fix matview access method change issue (#4959)

* Fix matview access method change issue

* Use pg function get_am_name

* Split view generation command into pieces

src/backend/distributed/commands/alter_table.c

@@ -34,6 +34,7 @@
 #include "catalog/pg_am.h"
 #include "columnar/columnar.h"
 #include "columnar/columnar_tableam.h"
+#include "commands/defrem.h"
 #include "distributed/colocation_utils.h"
 #include "distributed/commands.h"
 #include "distributed/commands/utility_hook.h"
@@ -199,6 +200,7 @@ static char * CreateWorkerChangeSequenceDependencyCommand(char *sequenceSchemaNa
 														  char *sourceName,
 														  char *targetSchemaName,
 														  char *targetName);
+static char * GetAccessMethodForMatViewIfExists(Oid viewOid);
 static bool WillRecreateForeignKeyToReferenceTable(Oid relationId,
 												   CascadeToColocatedOption cascadeOption);
 static void WarningsForDroppingForeignKeysWithDistributedTables(Oid relationId);
@@ -1126,13 +1128,28 @@ GetViewCreationCommandsOfTable(Oid relationId)
 		char *qualifiedViewName = quote_qualified_identifier(schemaName, viewName);
 		bool isMatView = get_rel_relkind(viewOid) == RELKIND_MATVIEW;
 
-		appendStringInfo(query,
-						 "CREATE %s VIEW %s AS %s",
-						 isMatView ? "MATERIALIZED" : "",
-						 qualifiedViewName,
-						 viewDefinition);
+		/* here we need to get the access method of the view to recreate it */
+		char *accessMethodName = GetAccessMethodForMatViewIfExists(viewOid);
+
+		appendStringInfoString(query, "CREATE ");
+
+		if (isMatView)
+		{
+			appendStringInfoString(query, "MATERIALIZED ");
+		}
+
+		appendStringInfo(query, "VIEW %s ", qualifiedViewName);
+
+		if (accessMethodName)
+		{
+			appendStringInfo(query, "USING %s ", accessMethodName);
+		}
+
+		appendStringInfo(query, "AS %s", viewDefinition);
+
 		commands = lappend(commands, makeTableDDLCommandString(query->data));
 	}
+
 	return commands;
 }
 
@@ -1517,6 +1534,32 @@ CreateWorkerChangeSequenceDependencyCommand(char *sequenceSchemaName, char *sequ
 }
 
 
+/*
+ * GetAccessMethodForMatViewIfExists returns if there's an access method
+ * set to the view with the given oid. Returns NULL otherwise.
+ */
+static char *
+GetAccessMethodForMatViewIfExists(Oid viewOid)
+{
+	char *accessMethodName = NULL;
+	Relation relation = try_relation_open(viewOid, AccessShareLock);
+	if (relation == NULL)
+	{
+		ereport(ERROR, (errmsg("cannot complete operation "
+							   "because no such view exists")));
+	}
+
+	Oid accessMethodOid = relation->rd_rel->relam;
+	if (OidIsValid(accessMethodOid))
+	{
+		accessMethodName = get_am_name(accessMethodOid);
+	}
+	relation_close(relation, NoLock);
+
+	return accessMethodName;
+}
+
+
 /*
  * WillRecreateForeignKeyToReferenceTable checks if the table of relationId has any foreign
  * key to a reference table, if conversion will be cascaded to colocated table this function

src/test/regress/expected/alter_distributed_table.out

@@ -917,5 +917,32 @@ NOTICE:  renaming the new table to alter_distributed_table.partition_lengths_123
 
 (1 row)
 
+-- verify that alter_distributed_table doesn't change the access methods for the views on the table
+CREATE TABLE test_am_matview(a int);
+SELECT create_distributed_table('test_am_matview' ,'a', colocate_with:='none');
+ create_distributed_table
+---------------------------------------------------------------------
+
+(1 row)
+
+CREATE MATERIALIZED VIEW test_mat_view_am USING COLUMNAR AS SELECT count(*), a FROM test_am_matview GROUP BY a ;
+SELECT alter_distributed_table('test_am_matview', shard_count:= 52);
+NOTICE:  creating a new table for alter_distributed_table.test_am_matview
+NOTICE:  moving the data of alter_distributed_table.test_am_matview
+NOTICE:  dropping the old alter_distributed_table.test_am_matview
+NOTICE:  drop cascades to materialized view test_mat_view_am
+CONTEXT:  SQL statement "DROP TABLE alter_distributed_table.test_am_matview CASCADE"
+NOTICE:  renaming the new table to alter_distributed_table.test_am_matview
+ alter_distributed_table
+---------------------------------------------------------------------
+
+(1 row)
+
+SELECT amname FROM pg_am WHERE oid IN (SELECT relam FROM pg_class WHERE relname ='test_mat_view_am');
+  amname
+---------------------------------------------------------------------
+ columnar
+(1 row)
+
 SET client_min_messages TO WARNING;
 DROP SCHEMA alter_distributed_table CASCADE;

src/test/regress/sql/alter_distributed_table.sql

@@ -308,5 +308,12 @@ ALTER TABLE partition_lengths RENAME TO partition_lengths_1234567890123456789012
 -- verify alter_distributed_table works with long partitioned table names
 SELECT alter_distributed_table('partition_lengths_12345678901234567890123456789012345678901234567890', shard_count := 17, cascade_to_colocated := false);
 
+-- verify that alter_distributed_table doesn't change the access methods for the views on the table
+CREATE TABLE test_am_matview(a int);
+SELECT create_distributed_table('test_am_matview' ,'a', colocate_with:='none');
+CREATE MATERIALIZED VIEW test_mat_view_am USING COLUMNAR AS SELECT count(*), a FROM test_am_matview GROUP BY a ;
+SELECT alter_distributed_table('test_am_matview', shard_count:= 52);
+SELECT amname FROM pg_am WHERE oid IN (SELECT relam FROM pg_class WHERE relname ='test_mat_view_am');
+
 SET client_min_messages TO WARNING;
 DROP SCHEMA alter_distributed_table CASCADE;