[PATCH]: ./Inherit-xact-properties-in-postgres-fdw-v2.patch

Author: Commitfest Bot

contrib/postgres_fdw/connection.c

@@ -843,6 +843,9 @@ do_sql_command_end(PGconn *conn, const char *sql, bool consume_input)
  * those scans.  A disadvantage is that we can't provide sane emulation of
  * READ COMMITTED behavior --- it would be nice if we had some other way to
  * control which remote queries share a snapshot.
+ *
+ * Note that we always start remote transactions with the same read/write
+ * and deferrable properties as the local (top-level) transaction.
  */
 static void
 begin_remote_xact(ConnCacheEntry *entry)
@@ -852,17 +855,23 @@ begin_remote_xact(ConnCacheEntry *entry)
 	/* Start main transaction if we haven't yet */
 	if (entry->xact_depth <= 0)
 	{
-		const char *sql;
+		StringInfoData sql;
 
 		elog(DEBUG3, "starting remote transaction on connection %p",
 			 entry->conn);
 
+		initStringInfo(&sql);
+		appendStringInfoString(&sql, "START TRANSACTION ISOLATION LEVEL ");
 		if (IsolationIsSerializable())
-			sql = "START TRANSACTION ISOLATION LEVEL SERIALIZABLE";
+			appendStringInfoString(&sql, "SERIALIZABLE");
 		else
-			sql = "START TRANSACTION ISOLATION LEVEL REPEATABLE READ";
+			appendStringInfoString(&sql, "REPEATABLE READ");
+		if (TopTransactionIsReadOnly())
+			appendStringInfoString(&sql, " READ ONLY");
+		if (XactDeferrable)
+			appendStringInfoString(&sql, " DEFERRABLE");
 		entry->changing_xact_state = true;
-		do_sql_command(entry->conn, sql);
+		do_sql_command(entry->conn, sql.data);
 		entry->xact_depth = 1;
 		entry->changing_xact_state = false;
 	}

contrib/postgres_fdw/expected/postgres_fdw.out

@@ -12309,6 +12309,78 @@ 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');
+INSERT INTO loct VALUES (1, 'foo'), (2, 'bar');
+SELECT * FROM loct;
+ f1 | f2  
+----+-----
+  1 | foo
+  2 | bar
+(2 rows)
+
+SELECT * FROM remt;  -- should work
+ f1 |   f2   
+----+--------
+  1 | foofoo
+  2 | barbar
+(2 rows)
+
+SELECT * FROM loct;
+ f1 |   f2   
+----+--------
+  1 | foofoo
+  2 | barbar
+(2 rows)
+
+START TRANSACTION READ ONLY;
+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;
+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 | foofoo
+  2 | barbar
+(2 rows)
+
+COMMIT;
+START TRANSACTION ISOLATION LEVEL SERIALIZABLE DEFERRABLE;
+SELECT * FROM remt;
+ f1 |   f2   
+----+--------
+  1 | foofoo
+  2 | barbar
+(2 rows)
+
+COMMIT;
+START TRANSACTION ISOLATION LEVEL SERIALIZABLE READ ONLY DEFERRABLE;
+SELECT * FROM remt;
+ f1 |   f2   
+----+--------
+  1 | foofoo
+  2 | barbar
+(2 rows)
+
+COMMIT;
+-- Clean up
+DROP FOREIGN TABLE remt;
+DROP VIEW locv;
+DROP FUNCTION locf();
+DROP TABLE loct;
+-- ===================================================================
 -- test parallel commit and parallel abort
 -- ===================================================================
 ALTER SERVER loopback OPTIONS (ADD parallel_commit 'true');

contrib/postgres_fdw/sql/postgres_fdw.sql

@@ -4187,6 +4187,48 @@ 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');
+
+INSERT INTO loct VALUES (1, 'foo'), (2, 'bar');
+SELECT * FROM loct;
+
+SELECT * FROM remt;  -- should work
+SELECT * FROM loct;
+
+START TRANSACTION READ ONLY;
+SELECT * FROM remt;  -- 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 VIEW locv;
+DROP FUNCTION locf();
+DROP TABLE loct;
+
 -- ===================================================================
 -- test parallel commit and parallel abort
 -- ===================================================================

doc/src/sgml/postgres-fdw.sgml

@@ -1077,6 +1077,22 @@ postgres=# SELECT postgres_fdw_disconnect_all();
    <productname>PostgreSQL</productname> release might modify these rules.
   </para>
 
+  <para>
+   The remote transaction is opened in the same read/write mode as the local
+   transaction: if the local transaction has been declared
+   <literal>READ ONLY</literal> at the top level, the remote transaction is
+   opened in <literal>READ ONLY</literal> mode, otherwise it is opened in
+   <literal>READ WRITE</literal> mode.
+  </para>
+
+  <para>
+   The remote transaction is also opened in the same deferrable mode as the
+   local transaction: if the local transaction has been declared
+   <literal>DEFERRABLE</literal> at the top level, the remote transaction is
+   opened in <literal>DEFERRABLE</literal> mode, otherwise it is opened in
+   <literal>NOT DEFERRABLE</literal> mode.
+  </para>
+
   <para>
    Note that it is currently not supported by
    <filename>postgres_fdw</filename> to prepare the remote transaction for

src/backend/access/transam/xact.c

@@ -1044,6 +1044,27 @@ TransactionStartedDuringRecovery(void)
 	return CurrentTransactionState->startedInRecovery;
 }
 
+/*
+ *	TopTransactionIsReadOnly
+ *
+ * Returns true if the transaction has been declared READ ONLY at the top
+ * level.
+ */
+bool
+TopTransactionIsReadOnly(void)
+{
+	TransactionState s = CurrentTransactionState;
+
+	if (s->nestingLevel == 1)
+		return XactReadOnly;
+	while (s->nestingLevel > 2)
+	{
+		Assert(s->parent != NULL);
+		s = s->parent;
+	}
+	return s->prevXactReadOnly;
+}
+
 /*
  *	EnterParallelMode
  */

src/include/access/xact.h

@@ -458,6 +458,7 @@ extern TimestampTz GetCurrentTransactionStopTimestamp(void);
 extern void SetCurrentStatementStartTimestamp(void);
 extern int	GetCurrentTransactionNestLevel(void);
 extern bool TransactionIdIsCurrentTransactionId(TransactionId xid);
+extern bool TopTransactionIsReadOnly(void);
 extern void CommandCounterIncrement(void);
 extern void ForceSyncCommit(void);
 extern void StartTransactionCommand(void);