postgres_fdw: Inherit the local transaction's access/deferrable modes.

Previously, postgres_fdw always 1) opened a remote transaction in READ
WRITE mode even when the local transaction was READ ONLY, causing a READ
ONLY transaction using it that references a foreign table mapped to a
remote view executing a volatile function to write in the remote side,
and 2) opened the remote transaction in NOT DEFERRABLE mode even when
the local transaction was DEFERRABLE, causing a SERIALIZABLE READ ONLY
DEFERRABLE transaction using it to abort due to a serialization failure
in the remote side.

To avoid these, modify postgres_fdw to open a remote transaction in the
same access/deferrable modes as the local transaction.  This commit also
modifies it to open a remote subtransaction in the same access mode as
the local subtransaction.

Although these issues exist since the introduction of postgres_fdw,
there have been no reports from the field.  So it seems fine to just fix
them in master only.

Author: Etsuro Fujita <[email protected]>
Reviewed-by: Ashutosh Bapat <[email protected]>
Reviewed-by: Tom Lane <[email protected]>
Discussion: https://postgr.es/m/CAPmGK16n_hcUUWuOdmeUS%2Bw4Q6dZvTEDHb%3DOP%3D5JBzo-M3QmpQ%40mail.gmail.com

1 files changed, 134 insertions, 0 deletions

diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out
index 2185b42bb4f..eb4716bed81 100644
--- a/contrib/postgres_fdw/expected/postgres_fdw.out
+++ b/contrib/postgres_fdw/expected/postgres_fdw.out
@@ -12384,6 +12384,140 @@ SELECT count(*) FROM remote_application_name
 DROP FOREIGN TABLE remote_application_name;
 DROP VIEW my_application_name;
 -- ===================================================================
+-- test read-only and/or deferrable transactions
+-- ===================================================================
+CREATE TABLE loct (f1 int, f2 text);
+CREATE FUNCTION locf() RETURNS SETOF loct LANGUAGE SQL AS
+  'UPDATE public.loct SET f2 = f2 || f2 RETURNING *';
+CREATE VIEW locv AS SELECT t.* FROM locf() t;
+CREATE FOREIGN TABLE remt (f1 int, f2 text)
+  SERVER loopback OPTIONS (table_name 'locv');
+CREATE FOREIGN TABLE remt2 (f1 int, f2 text)
+  SERVER loopback2 OPTIONS (table_name 'locv');
+INSERT INTO loct VALUES (1, 'foo'), (2, 'bar');
+START TRANSACTION READ ONLY;
+SAVEPOINT s;
+SELECT * FROM remt;  -- should fail
+ERROR:  cannot execute UPDATE in a read-only transaction
+CONTEXT:  SQL function "locf" statement 1
+remote SQL command: SELECT f1, f2 FROM public.locv
+ROLLBACK TO s;
+RELEASE SAVEPOINT s;
+SELECT * FROM remt;  -- should fail
+ERROR:  cannot execute UPDATE in a read-only transaction
+CONTEXT:  SQL function "locf" statement 1
+remote SQL command: SELECT f1, f2 FROM public.locv
+ROLLBACK;
+START TRANSACTION;
+SAVEPOINT s;
+SET transaction_read_only = on;
+SELECT * FROM remt;  -- should fail
+ERROR:  cannot execute UPDATE in a read-only transaction
+CONTEXT:  SQL function "locf" statement 1
+remote SQL command: SELECT f1, f2 FROM public.locv
+ROLLBACK TO s;
+RELEASE SAVEPOINT s;
+SET transaction_read_only = on;
+SELECT * FROM remt;  -- should fail
+ERROR:  cannot execute UPDATE in a read-only transaction
+CONTEXT:  SQL function "locf" statement 1
+remote SQL command: SELECT f1, f2 FROM public.locv
+ROLLBACK;
+START TRANSACTION;
+SAVEPOINT s;
+SELECT * FROM remt;  -- should work
+ f1 |   f2   
+----+--------
+  1 | foofoo
+  2 | barbar
+(2 rows)
+
+SET transaction_read_only = on;
+SELECT * FROM remt;  -- should fail
+ERROR:  cannot execute UPDATE in a read-only transaction
+CONTEXT:  SQL function "locf" statement 1
+remote SQL command: SELECT f1, f2 FROM public.locv
+ROLLBACK TO s;
+RELEASE SAVEPOINT s;
+SELECT * FROM remt;  -- should work
+ f1 |   f2   
+----+--------
+  1 | foofoo
+  2 | barbar
+(2 rows)
+
+SET transaction_read_only = on;
+SELECT * FROM remt;  -- should fail
+ERROR:  cannot execute UPDATE in a read-only transaction
+CONTEXT:  SQL function "locf" statement 1
+remote SQL command: SELECT f1, f2 FROM public.locv
+ROLLBACK;
+START TRANSACTION;
+SAVEPOINT s;
+SELECT * FROM remt;  -- should work
+ f1 |   f2   
+----+--------
+  1 | foofoo
+  2 | barbar
+(2 rows)
+
+SET transaction_read_only = on;
+SELECT * FROM remt2;  -- should fail
+ERROR:  cannot execute UPDATE in a read-only transaction
+CONTEXT:  SQL function "locf" statement 1
+remote SQL command: SELECT f1, f2 FROM public.locv
+ROLLBACK TO s;
+RELEASE SAVEPOINT s;
+SELECT * FROM remt;  -- should work
+ f1 |   f2   
+----+--------
+  1 | foofoo
+  2 | barbar
+(2 rows)
+
+SET transaction_read_only = on;
+SELECT * FROM remt2;  -- should fail
+ERROR:  cannot execute UPDATE in a read-only transaction
+CONTEXT:  SQL function "locf" statement 1
+remote SQL command: SELECT f1, f2 FROM public.locv
+ROLLBACK;
+DROP FOREIGN TABLE remt;
+CREATE FOREIGN TABLE remt (f1 int, f2 text)
+  SERVER loopback OPTIONS (table_name 'loct');
+START TRANSACTION ISOLATION LEVEL SERIALIZABLE READ ONLY;
+SELECT * FROM remt;
+ f1 | f2  
+----+-----
+  1 | foo
+  2 | bar
+(2 rows)
+
+COMMIT;
+START TRANSACTION ISOLATION LEVEL SERIALIZABLE DEFERRABLE;
+SELECT * FROM remt;
+ f1 | f2  
+----+-----
+  1 | foo
+  2 | bar
+(2 rows)
+
+COMMIT;
+START TRANSACTION ISOLATION LEVEL SERIALIZABLE READ ONLY DEFERRABLE;
+SELECT * FROM remt;
+ f1 | f2  
+----+-----
+  1 | foo
+  2 | bar
+(2 rows)
+
+COMMIT;
+-- Clean up
+DROP FOREIGN TABLE remt;
+DROP FOREIGN TABLE remt2;
+DROP VIEW locv;
+DROP FUNCTION locf();
+DROP TABLE loct;
+-- ===================================================================
 -- test parallel commit and parallel abort
 -- ===================================================================
 ALTER SERVER loopback OPTIONS (ADD parallel_commit 'true');