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

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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 <etsuro.fujita@gmail.com>
Reviewed-by: Ashutosh Bapat <ashutosh.bapat.oss@gmail.com>
Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us>
Discussion: https://postgr.es/m/CAPmGK16n_hcUUWuOdmeUS%2Bw4Q6dZvTEDHb%3DOP%3D5JBzo-M3QmpQ%40mail.gmail.com
This commit is contained in:
Etsuro Fujita
2025-06-01 17:30:00 +09:00
parent b006bcd531
commit e5a3c9d9b5
6 changed files with 347 additions and 8 deletions
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78
contrib/postgres_fdw/sql/postgres_fdw.sql
View File

@ -4200,6 +4200,84 @@ 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
ROLLBACK TO s;
RELEASE SAVEPOINT s;
SELECT * FROM remt; -- should fail
ROLLBACK;
START TRANSACTION;
SAVEPOINT s;
SET transaction_read_only = on;
SELECT * FROM remt; -- should fail
ROLLBACK TO s;
RELEASE SAVEPOINT s;
SET transaction_read_only = on;
SELECT * FROM remt; -- should fail
ROLLBACK;
START TRANSACTION;
SAVEPOINT s;
SELECT * FROM remt; -- should work
SET transaction_read_only = on;
SELECT * FROM remt; -- should fail
ROLLBACK TO s;
RELEASE SAVEPOINT s;
SELECT * FROM remt; -- should work
SET transaction_read_only = on;
SELECT * FROM remt; -- should fail
ROLLBACK;
START TRANSACTION;
SAVEPOINT s;
SELECT * FROM remt; -- should work
SET transaction_read_only = on;
SELECT * FROM remt2; -- should fail
ROLLBACK TO s;
RELEASE SAVEPOINT s;
SELECT * FROM remt; -- should work
SET transaction_read_only = on;
SELECT * FROM remt2; -- should fail
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;
COMMIT;
START TRANSACTION ISOLATION LEVEL SERIALIZABLE DEFERRABLE;
SELECT * FROM remt;
COMMIT;
START TRANSACTION ISOLATION LEVEL SERIALIZABLE READ ONLY DEFERRABLE;
SELECT * FROM remt;
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
-- ===================================================================