Fix tuple routing to initialize batching only for inserts

A cross-partition update on a partitioned table is implemented as a
delete followed by an insert. With foreign partitions, this was however
causing issues, because the FDW and core may disagree on when to enable
batching.  postgres_fdw was only allowing batching for plain inserts
(CMD_INSERT) while core was trying to batch the insert component of the
cross-partition update.  Fix by restricting core to apply batching only
to plain CMD_INSERT queries.

It's possible to allow batching for cross-partition updates, but that
will require more extensive changes, so better to leave that for a
separate patch.

Author: Amit Langote
Reviewed-by: Tomas Vondra, Takayuki Tsunakawa
Discussion: https://postgr.es/m/20200628151002.7x5laxwpgvkyiu3q@development

1 files changed, 18 insertions, 1 deletions

diff --git a/contrib/postgres_fdw/sql/postgres_fdw.sql b/contrib/postgres_fdw/sql/postgres_fdw.sql
index 151f4f18341..2b525ea44a8 100644
--- a/contrib/postgres_fdw/sql/postgres_fdw.sql
+++ b/contrib/postgres_fdw/sql/postgres_fdw.sql
@@ -2909,5 +2909,22 @@ CREATE TABLE batch_table_p2
 INSERT INTO batch_table SELECT * FROM generate_series(1, 66) i;
 SELECT COUNT(*) FROM batch_table;
 
+-- Check that enabling batched inserts doesn't interfere with cross-partition
+-- updates
+CREATE TABLE batch_cp_upd_test (a int) PARTITION BY LIST (a);
+CREATE TABLE batch_cp_upd_test1 (LIKE batch_cp_upd_test);
+CREATE FOREIGN TABLE batch_cp_upd_test1_f
+	PARTITION OF batch_cp_upd_test
+	FOR VALUES IN (1)
+	SERVER loopback
+	OPTIONS (table_name 'batch_cp_upd_test1', batch_size '10');
+CREATE TABLE batch_cp_up_test1 PARTITION OF batch_cp_upd_test
+	FOR VALUES IN (2);
+INSERT INTO batch_cp_upd_test VALUES (1), (2);
+
+-- The following moves a row from the local partition to the foreign one
+UPDATE batch_cp_upd_test t SET a = 1 FROM (VALUES (1), (2)) s(a) WHERE t.a = s.a;
+SELECT tableoid::regclass, * FROM batch_cp_upd_test;
+
 -- Clean up
-DROP TABLE batch_table CASCADE;
+DROP TABLE batch_table, batch_cp_upd_test CASCADE;