Switching to the new EngineFacadeby Roman Podoliaka

@rpodoliakairc: rpodolyakarpodolyaka@mirantis.com

slides: http://podoliaka.org/talks/

The new EngineFacadespec: https://specs.openstack.org/openstack/oslo­specs/specs/kilo/make­enginefacade­a­facade.htmlimplemented by zzzeek (Mike Bayer) in Liberty (oslo.db >=1.12.0)a new clean API for using of oslo.db

thread­safe initializationdeclarative management of session / connection scopeeasier offloading of read­only transactions toasynchronous replicas

"old" EngineFacade: thread­safe initialization is left upto users

_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 thread­safe initialization

from oslo.db import enginefacade as sql

@sql.readerdef some_api_method(context):    # work with context.session

@sql.writerdef some_other_api_method(context):    # work with context.session

"new" EngineFacade: multiple instances ofEngineFacade

main_context_manager = sql.transaction_context()api_context_manager = sql.transaction_context()

"new" EngineFacade: project specific configuration

context_manager = enginefacade.transaction_context()

context_manager.configure(sqlite_fk=True)context_manager.append_on_engine_create(set_hook)

"old" EngineFacade: get_session() boilerplate

@require_context@handle_db_data_errordef 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

@require_contextdef _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 manageddeclaratively

@main_context_manager.writerdef 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 thenew EngineFacade?

NovaNeutronIronicKeystone...

Need help?Slides: http://podoliaka.org/talks/

Bugs: https://bugs.launchpad.net/oslo.db

Questions:

IRC#openstack­oslo at freenodezzzeek (Mike Bayer)rpodolyaka (Roman Podoliaka)

MLhttp://lists.openstack.org/cgi­bin/mailman/listinfo/openstack­devtag with [oslo][db]