Handle engine creation inside of Connection object

We now store sqlalchemy engine object inside of our Connection object.
This allows us to open multiple concurrent connections.

Change-Id: I57b6d89f30c065643dbfab958e032f2adac59cd6

ceilometer/storage/impl_sqlalchemy.py

@@ -176,17 +176,26 @@ class Connection(base.Connection):
             conf.database.connection = \
                 os.environ.get('CEILOMETER_TEST_SQL_URL', url)
 
-    @staticmethod
+        # NOTE(Alexei_987) Related to bug #1271103
-    def _get_db_session():
+        #                  we steal objects from sqlalchemy_session
-        return sqlalchemy_session.get_session()
+        #                  to manage their lifetime on our own.
+        #                  This is needed to open several db connections
+        self._engine = sqlalchemy_session.get_engine()
+        self._maker = sqlalchemy_session.get_maker(self._engine)
+        sqlalchemy_session._ENGINE = None
+        sqlalchemy_session._MAKER = None
+
+    def _get_db_session(self):
+        return self._maker()
 
     def upgrade(self):
-        migration.db_sync(self._get_db_session().get_bind())
+        migration.db_sync(self._engine)
 
     def clear(self):
-        engine = self._get_db_session().get_bind()
         for table in reversed(models.Base.metadata.sorted_tables):
-            engine.execute(table.delete())
+            self._engine.execute(table.delete())
+        self._maker.close_all()
+        self._engine.dispose()
 
     @staticmethod
     def _create_or_update(session, model_class, _id, source=None, **kwargs):

ceilometer/storage/sqlalchemy/alembic/env.py

@@ -15,7 +15,6 @@ from logging import config as log_config
 
 from alembic import context
 
-import ceilometer.openstack.common.db.sqlalchemy.session as sqlalchemy_session
 from ceilometer.storage.sqlalchemy import models
 
 # this is the Alembic Config object, which provides
@@ -56,23 +55,20 @@ def run_migrations_offline():
         context.run_migrations()
 
 
-def run_migrations_online():
+def run_migrations_online(engine):
     """Run migrations in 'online' mode.
 
     In this scenario we need to create an Engine
     and associate a connection with the context.
 
     """
-    engine = sqlalchemy_session.get_session().get_bind()
-
     connection = engine.connect()
     context.configure(connection=connection, target_metadata=target_metadata)
 
     with context.begin_transaction():
         context.run_migrations()
-    connection.close()
 
 if context.is_offline_mode():
     run_migrations_offline()
 else:
-    run_migrations_online()
+    run_migrations_online(config._engine)

ceilometer/storage/sqlalchemy/migration.py

@@ -32,7 +32,9 @@ def db_sync(engine):
     db_version(engine)  # This is needed to create a version stamp in empty DB
     repository = _find_migrate_repo()
     versioning_api.upgrade(engine, repository)
-    alembic.command.upgrade(_alembic_config(), "head")
+    config = _alembic_config()
+    config._engine = engine
+    alembic.command.upgrade(config, "head")
 
 
 def _alembic_config():

ceilometer/tests/db.py

@@ -26,6 +26,7 @@ import warnings
 import six
 
 from ceilometer.openstack.common.fixture import config
+import ceilometer.openstack.common.fixture.mockpatch as oslo_mock
 from ceilometer import storage
 from ceilometer.tests import base as test_base
 
@@ -51,6 +52,9 @@ class TestBase(test_base.BaseTestCase):
                 self.skipTest(str(e))
         self.conn.upgrade()
 
+        self.useFixture(oslo_mock.Patch('ceilometer.storage.get_connection',
+                                        return_value=self.conn))
+
         self.CONF([], project='ceilometer')
 
         # Set a default location for the pipeline config file so the

ceilometer/tests/storage/test_impl_sqlalchemy.py

@@ -28,10 +28,11 @@ import repr
 
 from mock import patch
 
-import ceilometer.openstack.common.db.sqlalchemy.session as sqlalchemy_session
+from ceilometer.openstack.common.fixture import config
 from ceilometer.openstack.common import timeutils
 from ceilometer.storage import models
 from ceilometer.storage.sqlalchemy import models as sql_models
+from ceilometer.tests import base as tests_base
 from ceilometer.tests import db as tests_db
 from ceilometer.tests.storage import test_storage_scenarios as scenarios
 
@@ -172,21 +173,26 @@ class EventTest(EventTestBase):
         self.assertTrue(repr.repr(ev))
 
 
-class ModelTest(tests_db.TestBase):
+class ModelTest(tests_base.BaseTestCase):
     database_connection = 'mysql://localhost'
 
     def test_model_table_args(self):
+        self.CONF = self.useFixture(config.Config()).conf
+        self.CONF.set_override('connection', self.database_connection,
+                               group='database')
         self.assertIsNotNone(sql_models.table_args())
 
 
 class RelationshipTest(scenarios.DBTestBase):
-    database_connection = 'mysql://localhost'
+    # Note: Do not derive from SQLAlchemyEngineTestBase, since we
+    # don't want to automatically inherit all the Meter setup.
+    database_connection = 'sqlite://'
 
     def test_clear_metering_data_meta_tables(self):
         timeutils.utcnow.override_time = datetime.datetime(2012, 7, 2, 10, 45)
         self.conn.clear_expired_metering_data(3 * 60)
 
-        session = sqlalchemy_session.get_session()
+        session = self.conn._get_db_session()
         meta_tables = [sql_models.MetaText, sql_models.MetaFloat,
                        sql_models.MetaBigInt, sql_models.MetaBool]
         for table in meta_tables:
@@ -200,7 +206,7 @@ class RelationshipTest(scenarios.DBTestBase):
         timeutils.utcnow.override_time = datetime.datetime(2012, 7, 2, 10, 45)
         self.conn.clear_expired_metering_data(3 * 60)
 
-        session = sqlalchemy_session.get_session()
+        session = self.conn._get_db_session()
         self.assertEqual(session.query(sql_models.sourceassoc)
             .filter(~sql_models.sourceassoc.c.meter_id.in_(
                 session.query(sql_models.Meter.id)