Merge pull request #1 from malor/enginefacade

Slides for a lightning talk in Barcelona on EngineFacade

talks/enginefacade/slides.md

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+<!-- $theme: default -->
+
+Switching to the new EngineFacade
+=================================
+
+by Roman Podoliaka
+
+@rpodoliaka
+irc: **rpodolyaka**
+rpodolyaka@mirantis.com
+
+
+slides: http://podoliaka.org/talks/
+
+---
+
+The new EngineFacade
+====================
+
+* spec: https://specs.openstack.org/openstack/oslo-specs/specs/kilo/make-enginefacade-a-facade.html
+* implemented by **zzzeek** (Mike Bayer) in Liberty (oslo.db >= 1.12.0)
+* a new clean API for using of oslo.db
+	* thread-safe initialization
+	* declarative management of session / connection scope
+	* easier offloading of read-only transactions to asynchronous replicas
+
+---
+
+### "old" EngineFacade: thread-safe initialization is left up to users
+
+```python
+_ENGINE_FACADE = None
+_LOCK = threading.Lock()
+
+def _create_facade_lazily():
+    global _LOCK, _ENGINE_FACADE
+    if _ENGINE_FACADE is None:
+        with _LOCK:
+            if _ENGINE_FACADE is None:
+                _ENGINE_FACADE = db_session.EngineFacade.from_config(CONF)
+    return _ENGINE_FACADE
+```
+
+---
+
+### "new" EngineFacade: lazy thread-safe initialization
+
+```python
+from oslo.db import enginefacade as sql
+
+@sql.reader
+def some_api_method(context):
+    # work with context.session
+
+@sql.writer
+def some_other_api_method(context):
+    # work with context.session
+```
+
+---
+
+### "new" EngineFacade: multiple instances of EngineFacade
+
+```python
+main_context_manager = sql.transaction_context()
+api_context_manager = sql.transaction_context()
+```
+---
+
+### "new" EngineFacade: project specific configuration
+
+```python
+context_manager = enginefacade.transaction_context()
+
+context_manager.configure(sqlite_fk=True)
+context_manager.append_on_engine_create(set_hook)
+```
+
+---
+
+### "old" EngineFacade: get_session() boilerplate
+
+```python
+@require_context
+@handle_db_data_error
+def snapshot_create(context, values):
+    values['snapshot_metadata'] = \
+    	_metadata_refs(values.get('metadata'),
+         models.SnapshotMetadata)
+    if not values.get('id'):
+        values['id'] = str(uuid.uuid4())
+
+    session = get_session()
+    with session.begin():
+        snapshot_ref = models.Snapshot()
+        snapshot_ref.update(values)
+        session.add(snapshot_ref)
+
+        return _snapshot_get(context, values['id'],
+                             session=session)
+```
+
+---
+
+### "old" EngineFacade: private DB API functions
+
+```python
+@require_context
+def _snapshot_metadata_get(context, snapshot_id,
+                           session=None):
+    rows = _snapshot_metadata_get_query(
+    	context,snapshot_id, session).all()
+    result = {}
+    for row in rows:
+        result[row['key']] = row['value']
+
+    return result
+```
+
+---
+
+### "new" EngineFacade: session scope is managed declaratively
+
+```python
+@main_context_manager.writer
+def quota_destroy_all_by_project_and_user(context,
+                                          project_id,
+                                          user_id):
+    model_query(context, models.ProjectUserQuota,
+                read_deleted="no").\
+        filter_by(project_id=project_id).\
+        filter_by(user_id=user_id).\
+        soft_delete(synchronize_session=False)
+```
+
+---
+
+What projects are already using the new EngineFacade?
+=====================================================
+
+* [Nova](https://review.openstack.org/#/q/status:merged+project:openstack/nova+branch:master+topic:bp/new-oslodb-enginefacade)
+* [Neutron](https://review.openstack.org/#/q/status:merged+project:openstack/neutron+branch:master+topic:bp/enginefacade-switch)
+* [Ironic](https://review.openstack.org/#/q/status:merged+project:openstack/ironic+branch:master+topic:enginefacade)
+* [Keystone](https://review.openstack.org/#/c/257458/)
+* ...
+
+---
+
+Need help?
+==========
+
+Slides:  http://podoliaka.org/talks/
+
+Bugs: https://bugs.launchpad.net/oslo.db
+
+Questions:
+
+* IRC
+	* #openstack-oslo at freenode
+	* **zzzeek** (Mike Bayer)
+	* **rpodolyaka** (Roman Podoliaka)
+* ML
+	* http://lists.openstack.org/cgi-bin/mailman/listinfo/openstack-dev
+	* tag with **[oslo][db]**