Support sql_connection_debug to get SQL diagnostic information

We've had a few reports of SQL issues; it'll be very helpful to be able to get SQL information
into our log.

Bug #964844

Change-Id: I9d08991a3677bc6cbed45a930ede9271d685cac1

nova/db/sqlalchemy/session.py

@@ -93,6 +93,12 @@ def get_engine():
             'convert_unicode': True,
         }
 
+        # Map our SQL debug level to SQLAlchemy's options
+        if FLAGS.sql_connection_debug >= 100:
+            engine_args['echo'] = 'debug'
+        elif FLAGS.sql_connection_debug >= 50:
+            engine_args['echo'] = True
+
         if "sqlite" in connection_dict.drivername:
             engine_args["poolclass"] = NullPool
 

nova/flags.py

@@ -99,6 +99,10 @@ def _get_my_ip():
                default='sqlite:///$state_path/$sqlite_db',
                help='The SQLAlchemy connection string used to connect to the '
                     'database'),
+    cfg.IntOpt('sql_connection_debug',
+               default=0,
+               help='Verbosity of SQL debugging information. 0=None, '
+                    '100=Everything'),
     cfg.StrOpt('api_paste_config',
                default="api-paste.ini",
                help='File name for the paste.deploy config for nova-api'),