Fix bug: zombie record in gp_distribution_policy (#6768)

When a table has been transformed to a view by creating ON SELECT
rule, the record in gp_distribution_policy should be deleted also,
for there is no such record for a view.
Also, the relstorage in pg_class should be changed to 'v'.

src/backend/rewrite/rewriteDefine.c

@@ -549,6 +549,8 @@ DefineQueryRewrite(char *rulename,
 		/* drop storage while table still looks like a table  */
 		RelationDropStorage(event_relation);
 		DeleteSystemAttributeTuples(event_relid);
+		/* delete distribution policy record */
+		GpPolicyRemove(event_relid);
 
 		/*
 		 * Drop the toast table if any.  (This won't take care of updating the
@@ -585,8 +587,8 @@ DefineQueryRewrite(char *rulename,
 
 		/*
 		 * Fix pg_class entry to look like a normal view's, including setting
-		 * the correct relkind and removal of reltoastrelid of the toast table
-		 * we potentially removed above.
+		 * the correct relkind/relstorage and removal of reltoastrelid of the
+		 * toast table we potentially removed above.
 		 */
 		classTup = SearchSysCacheCopy1(RELOID, ObjectIdGetDatum(event_relid));
 		if (!HeapTupleIsValid(classTup))
@@ -600,6 +602,7 @@ DefineQueryRewrite(char *rulename,
 		classForm->reltoastrelid = InvalidOid;
 		classForm->relhasindex = false;
 		classForm->relkind = RELKIND_VIEW;
+		classForm->relstorage = RELSTORAGE_VIRTUAL;
 		classForm->relhasoids = false;
 		classForm->relhaspkey = false;
 		classForm->relfrozenxid = InvalidTransactionId;

src/test/regress/expected/gp_rules.out

@@ -8,6 +8,23 @@ NOTICE:  Table doesn't have 'DISTRIBUTED BY' clause -- Using column named 'a' as
 HINT:  The 'DISTRIBUTED BY' clause determines the distribution of data. Make sure column(s) chosen are the optimal data distribution key to minimize skew.
 CREATE rule "_RETURN" as on select to table_to_view_test1
         do instead select * from table_to_view_test2;
+-- relkind and relstorage have been changed to 'v'
+SELECT relkind, relstorage FROM pg_class
+    WHERE oid = 'table_to_view_test1'::regclass;
+ relkind | relstorage 
+---------+------------
+ v       | v
+(1 row)
+
+-- distribution policy record has been deleted
+SELECT 1 FROM gp_distribution_policy
+    WHERE localoid = 'table_to_view_test1'::regclass;
+ ?column? 
+----------
+(0 rows)
+
+DROP VIEW table_to_view_test1;
+DROP TABLE table_to_view_test2;
 -- Same for an Append-Only table. It is currently not supported.
 CREATE table aotable_to_view_test1 (a int) with (appendonly=true);
 NOTICE:  Table doesn't have 'DISTRIBUTED BY' clause -- Using column named 'a' as the Greenplum Database data distribution key for this table.

src/test/regress/sql/gp_rules.sql

@@ -7,6 +7,16 @@ CREATE table table_to_view_test2 (a int);
 CREATE rule "_RETURN" as on select to table_to_view_test1
         do instead select * from table_to_view_test2;
 
+-- relkind and relstorage have been changed to 'v'
+SELECT relkind, relstorage FROM pg_class
+    WHERE oid = 'table_to_view_test1'::regclass;
+-- distribution policy record has been deleted
+SELECT 1 FROM gp_distribution_policy
+    WHERE localoid = 'table_to_view_test1'::regclass;
+
+DROP VIEW table_to_view_test1;
+DROP TABLE table_to_view_test2;
+
 -- Same for an Append-Only table. It is currently not supported.
 
 CREATE table aotable_to_view_test1 (a int) with (appendonly=true);