Revert of the push of bug #20837 due to failing regression tests.

mysql-test/r/innodb_mysql.result

@@ -2273,35 +2273,4 @@ END|
 DROP PROCEDURE p1;
 DROP VIEW v1;
 DROP TABLE t1,t2;
-#
-# Bug #20837 Apparent change of isolation 
-#     level during transaction
-#
-SET SESSION TRANSACTION ISOLATION LEVEL REPEATABLE READ;
-CREATE TABLE t1 (s1 INT) ENGINE=InnoDB;
-INSERT INTO t1 VALUES (1),(2);
-COMMIT;
-SET @@autocommit = 0;
-COMMIT;
-SET TRANSACTION ISOLATION LEVEL READ UNCOMMITTED;
-START TRANSACTION;
-SELECT * FROM t1;
-s1
-1
-2
-Should be READ UNCOMMITTED
-SELECT @@tx_isolation;
-@@tx_isolation
-READ-UNCOMMITTED
-INSERT INTO t1 VALUES (-1);
-Should be READ UNCOMMITTED
-SELECT @@tx_isolation;
-@@tx_isolation
-READ-UNCOMMITTED
-COMMIT;
-Should now be REPEATABLE READ
-SELECT @@tx_isolation;
-@@tx_isolation
-REPEATABLE-READ
-DROP TABLE t1;
 End of 5.1 tests

mysql-test/t/innodb_mysql.test

@@ -536,30 +536,4 @@ DROP PROCEDURE p1;
 DROP VIEW v1;
 DROP TABLE t1,t2;
 
-
---echo #
---echo # Bug #20837 Apparent change of isolation 
---echo #     level during transaction
---echo #
-
-SET SESSION TRANSACTION ISOLATION LEVEL REPEATABLE READ;
-CREATE TABLE t1 (s1 INT) ENGINE=InnoDB;
-INSERT INTO t1 VALUES (1),(2);
-COMMIT;
-
-SET @@autocommit = 0;
-COMMIT;
-SET TRANSACTION ISOLATION LEVEL READ UNCOMMITTED;
-START TRANSACTION;
-SELECT * FROM t1;
---echo Should be READ UNCOMMITTED
-SELECT @@tx_isolation;
-INSERT INTO t1 VALUES (-1);
---echo Should be READ UNCOMMITTED
-SELECT @@tx_isolation;
-COMMIT;
---echo Should now be REPEATABLE READ
-SELECT @@tx_isolation;
-DROP TABLE t1;
-
 --echo End of 5.1 tests

sql/handler.cc

@@ -1369,14 +1369,8 @@ int ha_autocommit_or_rollback(THD *thd, int error)
       if (thd->transaction_rollback_request && !thd->in_sub_stmt)
         (void) ha_rollback(thd);
     }
-  } 
-  else if (!(thd->options & (OPTION_NOT_AUTOCOMMIT | OPTION_BEGIN)))
-  {
-    /* 
-       If we're in autocommit mode, reset tx_isolation
-       to the default value
-    */
-    thd->variables.tx_isolation= thd->session_tx_isolation;
+
+    thd->variables.tx_isolation=thd->session_tx_isolation;
   }
 #endif
   DBUG_RETURN(error);