Add a slave db handle for the SQLAlchemy backend.

Adds an option for a slave DB connection for scaling
purposes. Read queries can be sent here to spread out
db load a bit. This patch adds a new configuration option:
slave_connection.

Implements: blueprint db-slave-handle
Change-Id: I5cc5e0696e3fcd8609ee6b5466b0377ca52b8b58
DocImpact

1 files changed, 20 insertions, 0 deletions

diff --git a/tests/unit/db/sqlalchemy/test_sqlalchemy.py b/tests/unit/db/sqlalchemy/test_sqlalchemy.py
index b18825a..e548a3b 100644
--- a/tests/unit/db/sqlalchemy/test_sqlalchemy.py
+++ b/tests/unit/db/sqlalchemy/test_sqlalchemy.py
@@ -182,3 +182,23 @@ class RegexpFilterTestCase(test_utils.BaseTestCase):
 
     def test_regexp_filter_unicode_nomatch(self):
         self._test_regexp_filter(u'♦', [])
+
+
+class SlaveBackendTestCase(test_utils.BaseTestCase):
+
+    def test_slave_engine_nomatch(self):
+        default = session.CONF.database.connection
+        session.CONF.database.slave_connection = default
+
+        e = session.get_engine()
+        slave_e = session.get_engine(slave_engine=True)
+        self.assertNotEqual(slave_e, e)
+
+    def test_no_slave_engine_match(self):
+        slave_e = session.get_engine()
+        e = session.get_engine()
+        self.assertEqual(slave_e, e)
+
+    def test_slave_backend_nomatch(self):
+        session.CONF.database.slave_connection = "mysql:///localhost"
+        self.assertRaises(AssertionError, session._assert_matching_drivers)