Add possibility to disable sqlalchemy tracing

Engine that is used in migraiton shouldn't be traced.
So add built-in support for disable tracing.
This simplifies a lot code in OpenStack projects

osprofiler/profiler.py

@@ -49,14 +49,14 @@ def get_profiler():
 
 
 def start(name, info=None):
-    """Send new start notification if profiler instance is preseneted."""
+    """Send new start notification if profiler instance is presented."""
     profiler = get_profiler()
     if profiler:
         profiler.start(name, info=info)
 
 
 def stop(info=None):
-    """Send new stop notification if profiler instance is preseneted."""
+    """Send new stop notification if profiler instance is presented."""
     profiler = get_profiler()
     if profiler:
         profiler.stop(info=info)

osprofiler/sqlalchemy.py

@@ -37,8 +37,22 @@ def after_execute():
     return handler
 
 
+_DISABLED = False
+
+
+def disable():
+    global _DISABLED
+    _DISABLED = True
+
+
+def enable():
+    global _DISABLED
+    _DISABLED = False
+
+
 def add_tracing(sqlalchemy, engine, name):
     """Add tracing to all sqlalchemy calls."""
 
-    sqlalchemy.event.listen(engine, 'before_execute', before_execute(name))
-    sqlalchemy.event.listen(engine, 'after_execute', after_execute())
+    if not _DISABLED:
+        sqlalchemy.event.listen(engine, 'before_execute', before_execute(name))
+        sqlalchemy.event.listen(engine, 'after_execute', after_execute())

tests/test_sqlalchemy.py

@@ -58,3 +58,19 @@ class SqlalchemyTracingTestCase(test.TestCase):
             mock.call(engine, "after_execute", "after")
         ]
         self.assertEqual(sa.event.listen.call_args_list, expected_calls)
+
+    @mock.patch("osprofiler.sqlalchemy.before_execute")
+    @mock.patch("osprofiler.sqlalchemy.after_execute")
+    def test_disable_and_enable(self, mock_after_exc, mock_before_exc):
+        sqlalchemy.disable()
+
+        sa = mock.MagicMock()
+        engine = mock.MagicMock()
+        sqlalchemy.add_tracing(sa, engine, "sql")
+        self.assertFalse(mock_after_exc.called)
+        self.assertFalse(mock_before_exc.called)
+
+        sqlalchemy.enable()
+        sqlalchemy.add_tracing(sa, engine, "sql")
+        self.assertTrue(mock_after_exc.called)
+        self.assertTrue(mock_before_exc.called)