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

We concluded that commit e5a3c9d9b is a feature rather than a fix; since
it was added after feature freeze, revert it.

Reported-by: Fujii Masao <masao.fujii@oss.nttdata.com>
Reported-by: Michael Paquier <michael@paquier.xyz>
Reported-by: Robert Haas <robertmhaas@gmail.com>
Discussion: https://postgr.es/m/ed2296f1-1a6b-4932-b870-5bb18c2591ae%40oss.nttdata.com

contrib/postgres_fdw/connection.c

@@ -58,7 +58,6 @@ typedef struct ConnCacheEntry
 	/* Remaining fields are invalid when conn is NULL: */
 	int			xact_depth;		/* 0 = no xact open, 1 = main xact open, 2 =
 								 * one level of subxact open, etc */
-	bool		xact_read_only; /* xact r/o state */
 	bool		have_prep_stmt; /* have we prepared any stmts in this xact? */
 	bool		have_error;		/* have any subxacts aborted in this xact? */
 	bool		changing_xact_state;	/* xact state change in process */
@@ -85,12 +84,6 @@ static unsigned int prep_stmt_number = 0;
 /* tracks whether any work is needed in callback functions */
 static bool xact_got_connection = false;
 
-/*
- * tracks the nesting level of the topmost read-only transaction determined
- * by GetTopReadOnlyTransactionNestLevel()
- */
-static int	top_read_only_level = 0;
-
 /* custom wait event values, retrieved from shared memory */
 static uint32 pgfdw_we_cleanup_result = 0;
 static uint32 pgfdw_we_connect = 0;
@@ -379,7 +372,6 @@ make_new_connection(ConnCacheEntry *entry, UserMapping *user)
 
 	/* Reset all transient state fields, to be sure all are clean */
 	entry->xact_depth = 0;
-	entry->xact_read_only = false;
 	entry->have_prep_stmt = false;
 	entry->have_error = false;
 	entry->changing_xact_state = false;
@@ -851,81 +843,29 @@ 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 also that we always start the remote transaction with the same
- * read/write and deferrable properties as the local transaction, and start
- * the remote subtransaction with the same read/write property as the local
- * subtransaction.
  */
 static void
 begin_remote_xact(ConnCacheEntry *entry)
 {
 	int			curlevel = GetCurrentTransactionNestLevel();
 
-	/*
+	/* Start main transaction if we haven't yet */
-	 * Set the nesting level of the topmost read-only transaction if the
-	 * current transaction is read-only and we haven't yet.  Once it's set,
-	 * it's retained until that transaction is committed/aborted, and then
-	 * reset (see pgfdw_xact_callback and pgfdw_subxact_callback).
-	 */
-	if (XactReadOnly)
-	{
-		if (top_read_only_level == 0)
-			top_read_only_level = GetTopReadOnlyTransactionNestLevel();
-		Assert(top_read_only_level > 0);
-	}
-	else
-		Assert(top_read_only_level == 0);
-
-	/*
-	 * Start main transaction if we haven't yet; otherwise, change the
-	 * already-started remote transaction/subtransaction to read-only if the
-	 * local transaction/subtransaction have been done so after starting them
-	 * and we haven't yet.
-	 */
 	if (entry->xact_depth <= 0)
 	{
-		StringInfoData sql;
+		const char *sql;
-		bool		ro = (top_read_only_level == 1);
 
 		elog(DEBUG3, "starting remote transaction on connection %p",
 			 entry->conn);
 
-		initStringInfo(&sql);
-		appendStringInfoString(&sql, "START TRANSACTION ISOLATION LEVEL ");
 		if (IsolationIsSerializable())
-			appendStringInfoString(&sql, "SERIALIZABLE");
+			sql = "START TRANSACTION ISOLATION LEVEL SERIALIZABLE";
 		else
-			appendStringInfoString(&sql, "REPEATABLE READ");
+			sql = "START TRANSACTION ISOLATION LEVEL REPEATABLE READ";
-		if (ro)
-			appendStringInfoString(&sql, " READ ONLY");
-		if (XactDeferrable)
-			appendStringInfoString(&sql, " DEFERRABLE");
 		entry->changing_xact_state = true;
-		do_sql_command(entry->conn, sql.data);
+		do_sql_command(entry->conn, sql);
 		entry->xact_depth = 1;
-		if (ro)
-		{
-			Assert(!entry->xact_read_only);
-			entry->xact_read_only = true;
-		}
 		entry->changing_xact_state = false;
 	}
-	else if (!entry->xact_read_only)
-	{
-		Assert(top_read_only_level == 0 ||
-			   entry->xact_depth <= top_read_only_level);
-		if (entry->xact_depth == top_read_only_level)
-		{
-			entry->changing_xact_state = true;
-			do_sql_command(entry->conn, "SET transaction_read_only = on");
-			entry->xact_read_only = true;
-			entry->changing_xact_state = false;
-		}
-	}
-	else
-		Assert(top_read_only_level > 0 &&
-			   entry->xact_depth >= top_read_only_level);
 
 	/*
 	 * If we're in a subtransaction, stack up savepoints to match our level.
@@ -934,21 +874,12 @@ begin_remote_xact(ConnCacheEntry *entry)
 	 */
 	while (entry->xact_depth < curlevel)
 	{
-		StringInfoData sql;
+		char		sql[64];
-		bool		ro = (entry->xact_depth + 1 == top_read_only_level);
 
-		initStringInfo(&sql);
+		snprintf(sql, sizeof(sql), "SAVEPOINT s%d", entry->xact_depth + 1);
-		appendStringInfo(&sql, "SAVEPOINT s%d", entry->xact_depth + 1);
-		if (ro)
-			appendStringInfoString(&sql, "; SET transaction_read_only = on");
 		entry->changing_xact_state = true;
-		do_sql_command(entry->conn, sql.data);
+		do_sql_command(entry->conn, sql);
 		entry->xact_depth++;
-		if (ro)
-		{
-			Assert(!entry->xact_read_only);
-			entry->xact_read_only = true;
-		}
 		entry->changing_xact_state = false;
 	}
 }
@@ -1243,9 +1174,6 @@ pgfdw_xact_callback(XactEvent event, void *arg)
 
 	/* Also reset cursor numbering for next transaction */
 	cursor_number = 0;
-
-	/* Likewise for top_read_only_level */
-	top_read_only_level = 0;
 }
 
 /*
@@ -1344,10 +1272,6 @@ pgfdw_subxact_callback(SubXactEvent event, SubTransactionId mySubid,
 									   false);
 		}
 	}
-
-	/* If in the topmost read-only transaction, reset top_read_only_level */
-	if (curlevel == top_read_only_level)
-		top_read_only_level = 0;
 }
 
 /*
@@ -1450,9 +1374,6 @@ pgfdw_reset_xact_state(ConnCacheEntry *entry, bool toplevel)
 		/* Reset state to show we're out of a transaction */
 		entry->xact_depth = 0;
 
-		/* Reset xact r/o state */
-		entry->xact_read_only = false;
-
 		/*
 		 * If the connection isn't in a good idle state, it is marked as
 		 * invalid or keep_connections option of its server is disabled, then
@@ -1473,10 +1394,6 @@ pgfdw_reset_xact_state(ConnCacheEntry *entry, bool toplevel)
 	{
 		/* Reset state to show we're out of a subtransaction */
 		entry->xact_depth--;
-
-		/* If in the topmost read-only transaction, reset xact r/o state */
-		if (entry->xact_depth + 1 == top_read_only_level)
-			entry->xact_read_only = false;
 	}
 }
 

contrib/postgres_fdw/expected/postgres_fdw.out

@@ -12384,140 +12384,6 @@ 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');

contrib/postgres_fdw/sql/postgres_fdw.sql

@@ -4200,84 +4200,6 @@ 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
 -- ===================================================================

doc/src/sgml/postgres-fdw.sgml

@@ -1077,21 +1077,6 @@ 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 is <literal>READ ONLY</literal>,
-   the remote transaction is opened in <literal>READ ONLY</literal> mode,
-   otherwise it is opened in <literal>READ WRITE</literal> mode.
-   (This rule is also applied to remote and local subtransactions.)
-  </para>
-
-  <para>
-   The remote transaction is also opened in the same deferrable mode as the
-   local transaction: if the local transaction is <literal>DEFERRABLE</literal>,
-   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

@@ -1044,34 +1044,6 @@ TransactionStartedDuringRecovery(void)
 	return CurrentTransactionState->startedInRecovery;
 }
 
-/*
- *	GetTopReadOnlyTransactionNestLevel
- *
- * Note: this will return zero when not inside any transaction or when neither
- * a top-level transaction nor subtransactions are read-only, one when the
- * top-level transaction is read-only, two when one level of subtransaction is
- * read-only, etc.
- *
- * Note: subtransactions of the topmost read-only transaction are also
- * read-only, because they inherit read-only mode from the transaction, and
- * thus can't change to read-write mode.  See check_transaction_read_only().
- */
-int
-GetTopReadOnlyTransactionNestLevel(void)
-{
-	TransactionState s = CurrentTransactionState;
-
-	if (!XactReadOnly)
-		return 0;
-	while (s->nestingLevel > 1)
-	{
-		if (!s->prevXactReadOnly)
-			return s->nestingLevel;
-		s = s->parent;
-	}
-	return s->nestingLevel;
-}
-
 /*
  *	EnterParallelMode
  */

src/include/access/xact.h

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