Disable WAL-skipping optimization for COPY on views

COPY can skip writing WAL when loading data on a table which has been
created in the same transaction as the one loading the data, however
this cannot work on views as this would result in trying to flush
relation files which do not exist.  So disable the optimization so as
commands are able to work the same way with any configuration of
wal_level.

A test is added to cover this case, which needs to have wal_level set to
minimal to allow the problem to show up, and that is not the default
configuration.

Reported-by: Etsuro Fujita
Author: Michael Paquier
Reviewed-by: Etsuro Fujita
Discussion: https://postgr.es/m/15552-c64aa14c5c22f63c@postgresql.org
Backpatch-through: 10, where support for COPY on views has been added,
while v11 has added support for COPY on foreign tables.

src/backend/commands/copy.c

@@ -2408,10 +2408,15 @@ CopyFrom(CopyState cstate)
 	 * possible to improve on this, but it does mean maintaining heap insert
 	 * option flags per partition and setting them when we first open the
 	 * partition.
+	 *
+	 * This optimization is not supported for relation types which do not
+	 * have any physical storage, with views entering in this category.
+	 * Partitioned tables are not supported as per the description above.
 	 *----------
 	 */
 	/* createSubid is creation check, newRelfilenodeSubid is truncation check */
 	if (cstate->rel->rd_rel->relkind != RELKIND_PARTITIONED_TABLE &&
+		cstate->rel->rd_rel->relkind != RELKIND_VIEW &&
 		(cstate->rel->rd_createSubid != InvalidSubTransactionId ||
 		 cstate->rel->rd_newRelfilenodeSubid != InvalidSubTransactionId))
 	{

src/test/regress/expected/copy2.out

@@ -557,6 +557,23 @@ SELECT * FROM instead_of_insert_tbl;
   1 | test1
 (1 row)
 
+-- Test of COPY optimization with view using INSTEAD OF INSERT
+-- trigger when relation is created in the same transaction as
+-- when COPY is executed.
+BEGIN;
+CREATE VIEW instead_of_insert_tbl_view_2 as select ''::text as str;
+CREATE TRIGGER trig_instead_of_insert_tbl_view_2
+  INSTEAD OF INSERT ON instead_of_insert_tbl_view_2
+  FOR EACH ROW EXECUTE PROCEDURE fun_instead_of_insert_tbl();
+COPY instead_of_insert_tbl_view_2 FROM stdin;
+SELECT * FROM instead_of_insert_tbl;
+ id | name  
+----+-------
+  1 | test1
+  2 | test1
+(2 rows)
+
+COMMIT;
 -- clean up
 DROP TABLE forcetest;
 DROP TABLE vistest;
@@ -569,4 +586,5 @@ DROP FUNCTION fn_x_before();
 DROP FUNCTION fn_x_after();
 DROP TABLE instead_of_insert_tbl;
 DROP VIEW instead_of_insert_tbl_view;
+DROP VIEW instead_of_insert_tbl_view_2;
 DROP FUNCTION fun_instead_of_insert_tbl();

src/test/regress/sql/copy2.sql

@@ -411,6 +411,21 @@ test1
 
 SELECT * FROM instead_of_insert_tbl;
 
+-- Test of COPY optimization with view using INSTEAD OF INSERT
+-- trigger when relation is created in the same transaction as
+-- when COPY is executed.
+BEGIN;
+CREATE VIEW instead_of_insert_tbl_view_2 as select ''::text as str;
+CREATE TRIGGER trig_instead_of_insert_tbl_view_2
+  INSTEAD OF INSERT ON instead_of_insert_tbl_view_2
+  FOR EACH ROW EXECUTE PROCEDURE fun_instead_of_insert_tbl();
+
+COPY instead_of_insert_tbl_view_2 FROM stdin;
+test1
+\.
+
+SELECT * FROM instead_of_insert_tbl;
+COMMIT;
 
 -- clean up
 DROP TABLE forcetest;
@@ -424,4 +439,5 @@ DROP FUNCTION fn_x_before();
 DROP FUNCTION fn_x_after();
 DROP TABLE instead_of_insert_tbl;
 DROP VIEW instead_of_insert_tbl_view;
+DROP VIEW instead_of_insert_tbl_view_2;
 DROP FUNCTION fun_instead_of_insert_tbl();