Reservations support

Add the concept of resource reservation in neutron.
Usage tracking logic is also updated to support reservations.
Reservations are not however available with the now deprecated
configuration-based quota driver.

The base API controller will now use reservations to perform
quota checks rather than counting resource usage and then
invoking the limit_check routine.

The limit_check routine however has not been removed and
depreacated as a part of this patch. In order to ensure all
quota drivers expose a consistent interface, a
make_reservation method has been added to the configuration
based driver as well. This method simply performs "old-style"
limit checks by counting resource usage and then invoking
limit_check.

DocImpact

Implements blueprint better-quotas.

Change-Id: Ifea07f461def564884af5b291c8a56655a4d818b

neutron/api/v2/base.py

@@ -416,13 +416,15 @@ class Controller(object):
         if self._collection in body:
             # Have to account for bulk create
             items = body[self._collection]
-            deltas = {}
-            bulk = True
         else:
             items = [body]
-            bulk = False
         # Ensure policy engine is initialized
         policy.init()
+        # Store requested resource amounts grouping them by tenant
+        # This won't work with multiple resources. However because of the
+        # current structure of this controller there will hardly be more than
+        # one resource for which reservations are being made
+        request_deltas = {}
         for item in items:
             self._validate_network_tenant_ownership(request,
                                                     item[self._resource])
@@ -433,30 +435,34 @@ class Controller(object):
             if 'tenant_id' not in item[self._resource]:
                 # no tenant_id - no quota check
                 continue
-            try:
-                tenant_id = item[self._resource]['tenant_id']
-                count = quota.QUOTAS.count(request.context, self._resource,
-                                           self._plugin, tenant_id)
-                if bulk:
-                    delta = deltas.get(tenant_id, 0) + 1
-                    deltas[tenant_id] = delta
-                else:
-                    delta = 1
-                kwargs = {self._resource: count + delta}
-            except exceptions.QuotaResourceUnknown as e:
+            tenant_id = item[self._resource]['tenant_id']
+            delta = request_deltas.get(tenant_id, 0)
+            delta = delta + 1
+            request_deltas[tenant_id] = delta
+        # Quota enforcement
+        reservations = []
+        try:
+            for tenant in request_deltas:
+                reservation = quota.QUOTAS.make_reservation(
+                    request.context,
+                    tenant,
+                    {self._resource:
+                     request_deltas[tenant]},
+                    self._plugin)
+                reservations.append(reservation)
+        except exceptions.QuotaResourceUnknown as e:
                 # We don't want to quota this resource
                 LOG.debug(e)
-            else:
-                quota.QUOTAS.limit_check(request.context,
-                                         item[self._resource]['tenant_id'],
-                                         **kwargs)
 
         def notify(create_result):
             # Ensure usage trackers for all resources affected by this API
             # operation are marked as dirty
-            # TODO(salv-orlando): This operation will happen in a single
-            # transaction with reservation commit once that is implemented
-            resource_registry.set_resources_dirty(request.context)
+            with request.context.session.begin():
+                # Commit the reservation(s)
+                for reservation in reservations:
+                    quota.QUOTAS.commit_reservation(
+                        request.context, reservation.reservation_id)
+                resource_registry.set_resources_dirty(request.context)
 
             notifier_method = self._resource + '.create.end'
             self._notifier.info(request.context,
@@ -467,11 +473,35 @@ class Controller(object):
                                          notifier_method)
             return create_result
 
-        kwargs = {self._parent_id_name: parent_id} if parent_id else {}
+        def do_create(body, bulk=False, emulated=False):
+            kwargs = {self._parent_id_name: parent_id} if parent_id else {}
+            if bulk and not emulated:
+                obj_creator = getattr(self._plugin, "%s_bulk" % action)
+            else:
+                obj_creator = getattr(self._plugin, action)
+            try:
+                if emulated:
+                    return self._emulate_bulk_create(obj_creator, request,
+                                                     body, parent_id)
+                else:
+                    if self._collection in body:
+                        # This is weird but fixing it requires changes to the
+                        # plugin interface
+                        kwargs.update({self._collection: body})
+                    else:
+                        kwargs.update({self._resource: body})
+                    return obj_creator(request.context, **kwargs)
+            except Exception:
+                # In case of failure the plugin will always raise an
+                # exception. Cancel the reservation
+                with excutils.save_and_reraise_exception():
+                    for reservation in reservations:
+                        quota.QUOTAS.cancel_reservation(
+                            request.context, reservation.reservation_id)
+
         if self._collection in body and self._native_bulk:
             # plugin does atomic bulk create operations
-            obj_creator = getattr(self._plugin, "%s_bulk" % action)
-            objs = obj_creator(request.context, body, **kwargs)
+            objs = do_create(body, bulk=True)
             # Use first element of list to discriminate attributes which
             # should be removed because of authZ policies
             fields_to_strip = self._exclude_attributes_by_policy(
@@ -480,15 +510,12 @@ class Controller(object):
                 request.context, obj, fields_to_strip=fields_to_strip)
                 for obj in objs]})
         else:
-            obj_creator = getattr(self._plugin, action)
             if self._collection in body:
                 # Emulate atomic bulk behavior
-                objs = self._emulate_bulk_create(obj_creator, request,
-                                                 body, parent_id)
+                objs = do_create(body, bulk=True, emulated=True)
                 return notify({self._collection: objs})
             else:
-                kwargs.update({self._resource: body})
-                obj = obj_creator(request.context, **kwargs)
+                obj = do_create(body)
                 self._send_nova_notification(action, {},
                                              {self._resource: obj})
                 return notify({self._resource: self._view(request.context,

neutron/db/migration/alembic_migrations/versions/HEADS

@@ -1,3 +1,3 @@
 2a16083502f3
-48153cb5f051
+9859ac9c136
 kilo

neutron/db/migration/alembic_migrations/versions/liberty/expand/9859ac9c136_quota_reservations.py

@@ -0,0 +1,47 @@
+# Copyright 2015 OpenStack Foundation
+#
+#    Licensed under the Apache License, Version 2.0 (the "License"); you may
+#    not use this file except in compliance with the License. You may obtain
+#    a copy of the License at
+#
+#         http://www.apache.org/licenses/LICENSE-2.0
+#
+#    Unless required by applicable law or agreed to in writing, software
+#    distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+#    WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+#    License for the specific language governing permissions and limitations
+#    under the License.
+#
+
+"""quota_reservations
+
+Revision ID: 9859ac9c136
+Revises: 48153cb5f051
+Create Date: 2015-03-11 06:40:56.775075
+
+"""
+
+# revision identifiers, used by Alembic.
+revision = '9859ac9c136'
+down_revision = '48153cb5f051'
+
+from alembic import op
+import sqlalchemy as sa
+
+
+def upgrade():
+    op.create_table(
+        'reservations',
+        sa.Column('id', sa.String(length=36), nullable=False),
+        sa.Column('tenant_id', sa.String(length=255), nullable=True),
+        sa.Column('expiration', sa.DateTime(), nullable=True),
+        sa.PrimaryKeyConstraint('id'))
+
+    op.create_table(
+        'resourcedeltas',
+        sa.Column('resource', sa.String(length=255), nullable=False),
+        sa.Column('reservation_id', sa.String(length=36), nullable=False),
+        sa.Column('amount', sa.Integer(), nullable=True),
+        sa.ForeignKeyConstraint(['reservation_id'], ['reservations.id'],
+                                ondelete='CASCADE'),
+        sa.PrimaryKeyConstraint('resource', 'reservation_id'))

neutron/db/quota/api.py

@@ -13,11 +13,21 @@
 #    under the License.
 
 import collections
+import datetime
+
+import sqlalchemy as sa
+from sqlalchemy.orm import exc as orm_exc
+from sqlalchemy import sql
 
 from neutron.db import common_db_mixin as common_db_api
 from neutron.db.quota import models as quota_models
 
 
+# Wrapper for utcnow - needed for mocking it in unit tests
+def utcnow():
+    return datetime.datetime.utcnow()
+
+
 class QuotaUsageInfo(collections.namedtuple(
     'QuotaUsageInfo', ['resource', 'tenant_id', 'used', 'reserved', 'dirty'])):
 
@@ -27,6 +37,32 @@ class QuotaUsageInfo(collections.namedtuple(
         return self.reserved + self.used
 
 
+class ReservationInfo(object):
+    """Information about a resource reservation."""
+
+    def __init__(self, reservation_id, tenant_id, expiration, deltas):
+        self._reservation_id = reservation_id
+        self._tenant_id = tenant_id
+        self._expiration = expiration
+        self._deltas = deltas
+
+    @property
+    def reservation_id(self):
+        return self._reservation_id
+
+    @property
+    def tenant_id(self):
+        return self._tenant_id
+
+    @property
+    def expiration(self):
+        return self._expiration
+
+    @property
+    def deltas(self):
+        return self._deltas
+
+
 def get_quota_usage_by_resource_and_tenant(context, resource, tenant_id,
                                            lock_for_update=False):
     """Return usage info for a given resource and tenant.
@@ -157,3 +193,105 @@ def set_all_quota_usage_dirty(context, resource, dirty=True):
     query = common_db_api.model_query(context, quota_models.QuotaUsage)
     query = query.filter_by(resource=resource)
     return query.update({'dirty': dirty})
+
+
+def create_reservation(context, tenant_id, deltas, expiration=None):
+    # This method is usually called from within another transaction.
+    # Consider using begin_nested
+    with context.session.begin(subtransactions=True):
+        expiration = expiration or (utcnow() + datetime.timedelta(0, 120))
+        resv = quota_models.Reservation(tenant_id=tenant_id,
+                                        expiration=expiration)
+        context.session.add(resv)
+        for (resource, delta) in deltas.items():
+            context.session.add(
+                quota_models.ResourceDelta(resource=resource,
+                                           amount=delta,
+                                           reservation=resv))
+        # quota_usage for all resources involved in this reservation must
+        # be marked as dirty
+        set_resources_quota_usage_dirty(
+            context, deltas.keys(), tenant_id)
+    return ReservationInfo(resv['id'],
+                           resv['tenant_id'],
+                           resv['expiration'],
+                           dict((delta.resource, delta.amount)
+                                for delta in resv.resource_deltas))
+
+
+def get_reservation(context, reservation_id):
+    query = context.session.query(quota_models.Reservation).filter_by(
+        id=reservation_id)
+    resv = query.first()
+    if not resv:
+        return
+    return ReservationInfo(resv['id'],
+                           resv['tenant_id'],
+                           resv['expiration'],
+                           dict((delta.resource, delta.amount)
+                                for delta in resv.resource_deltas))
+
+
+def remove_reservation(context, reservation_id, set_dirty=False):
+    delete_query = context.session.query(quota_models.Reservation).filter_by(
+        id=reservation_id)
+    # Not handling MultipleResultsFound as the query is filtering by primary
+    # key
+    try:
+        reservation = delete_query.one()
+    except orm_exc.NoResultFound:
+        # TODO(salv-orlando): Raise here and then handle the exception?
+        return
+    tenant_id = reservation.tenant_id
+    resources = [delta.resource for delta in reservation.resource_deltas]
+    num_deleted = delete_query.delete()
+    if set_dirty:
+        # quota_usage for all resource involved in this reservation must
+        # be marked as dirty
+        set_resources_quota_usage_dirty(context, resources, tenant_id)
+    return num_deleted
+
+
+def get_reservations_for_resources(context, tenant_id, resources,
+                                   expired=False):
+    """Retrieve total amount of reservations for specified resources.
+
+    :param context: Neutron context with db session
+    :param tenant_id: Tenant identifier
+    :param resources: Resources for which reserved amounts should be fetched
+    :param expired: False to fetch active reservations, True to fetch expired
+                    reservations (defaults to False)
+    :returns: a dictionary mapping resources with corresponding deltas
+    """
+    if not resources:
+        # Do not waste time
+        return
+    now = utcnow()
+    resv_query = context.session.query(
+        quota_models.ResourceDelta.resource,
+        quota_models.Reservation.expiration,
+        sql.func.sum(quota_models.ResourceDelta.amount)).join(
+        quota_models.Reservation)
+    if expired:
+        exp_expr = (quota_models.Reservation.expiration < now)
+    else:
+        exp_expr = (quota_models.Reservation.expiration >= now)
+    resv_query = resv_query.filter(sa.and_(
+        quota_models.Reservation.tenant_id == tenant_id,
+        quota_models.ResourceDelta.resource.in_(resources),
+        exp_expr)).group_by(
+        quota_models.ResourceDelta.resource)
+    return dict((resource, total_reserved)
+           for (resource, exp, total_reserved) in resv_query)
+
+
+def remove_expired_reservations(context, tenant_id=None):
+    now = utcnow()
+    resv_query = context.session.query(quota_models.Reservation)
+    if tenant_id:
+        tenant_expr = (quota_models.Reservation.tenant_id == tenant_id)
+    else:
+        tenant_expr = sql.true()
+    resv_query = resv_query.filter(sa.and_(
+        tenant_expr, quota_models.Reservation.expiration < now))
+    return resv_query.delete()

neutron/db/quota/driver.py

@@ -13,9 +13,16 @@
 #    License for the specific language governing permissions and limitations
 #    under the License.
 
+from oslo_db import api as oslo_db_api
+from oslo_log import log
+
 from neutron.common import exceptions
+from neutron.db import api as db_api
+from neutron.db.quota import api as quota_api
 from neutron.db.quota import models as quota_models
 
+LOG = log.getLogger(__name__)
+
 
 class DbQuotaDriver(object):
     """Driver to perform necessary checks to enforce quotas and obtain quota
@@ -42,7 +49,8 @@ class DbQuotaDriver(object):
         # update with tenant specific limits
         q_qry = context.session.query(quota_models.Quota).filter_by(
             tenant_id=tenant_id)
-        tenant_quota.update((q['resource'], q['limit']) for q in q_qry)
+        for item in q_qry:
+            tenant_quota[item['resource']] = item['limit']
 
         return tenant_quota
 
@@ -116,6 +124,112 @@ class DbQuotaDriver(object):
 
         return dict((k, v) for k, v in quotas.items())
 
+    def _handle_expired_reservations(self, context, tenant_id,
+                                     resource, expired_amount):
+        LOG.debug(("Adjusting usage for resource %(resource)s: "
+                   "removing %(expired)d reserved items"),
+                  {'resource': resource,
+                   'expired': expired_amount})
+        # TODO(salv-orlando): It should be possible to do this
+        # operation for all resources with a single query.
+        # Update reservation usage
+        quota_api.set_quota_usage(
+            context,
+            resource,
+            tenant_id,
+            reserved=-expired_amount,
+            delta=True)
+        # Delete expired reservations (we don't want them to accrue
+        # in the database)
+        quota_api.remove_expired_reservations(
+            context, tenant_id=tenant_id)
+
+    @oslo_db_api.wrap_db_retry(max_retries=db_api.MAX_RETRIES,
+                               retry_on_request=True,
+                               retry_on_deadlock=True)
+    def make_reservation(self, context, tenant_id, resources, deltas, plugin):
+        # Lock current reservation table
+        # NOTE(salv-orlando): This routine uses DB write locks.
+        # These locks are acquired by the count() method invoked on resources.
+        # Please put your shotguns aside.
+        # A non locking algorithm for handling reservation is feasible, however
+        # it will require two database writes even in cases when there are not
+        # concurrent reservations.
+        # For this reason it might be advisable to handle contention using
+        # this kind of locks and paying the cost of a write set certification
+        # failure when a mysql galera cluster is employed. Also, this class of
+        # locks should be ok to use when support for sending "hotspot" writes
+        # to a single node will be avaialable.
+        requested_resources = deltas.keys()
+        with context.session.begin():
+            # Gather current usage information
+            # TODO(salv-orlando): calling count() for every resource triggers
+            # multiple queries on quota usage. This should be improved, however
+            # this is not an urgent matter as the REST API currently only
+            # allows allocation of a resource at a time
+            # NOTE: pass plugin too for compatibility with CountableResource
+            # instances
+            current_usages = dict(
+                (resource, resources[resource].count(
+                    context, plugin, tenant_id)) for
+                resource in requested_resources)
+            # get_tenant_quotes needs in inout a dictionary mapping resource
+            # name to BaseResosurce instances so that the default quota can be
+            # retrieved
+            current_limits = self.get_tenant_quotas(
+                context, resources, tenant_id)
+            # Adjust for expired reservations. Apparently it is cheaper than
+            # querying everytime for active reservations and counting overall
+            # quantity of resources reserved
+            expired_deltas = quota_api.get_reservations_for_resources(
+                context, tenant_id, requested_resources, expired=True)
+            # Verify that the request can be accepted with current limits
+            resources_over_limit = []
+            for resource in requested_resources:
+                expired_reservations = expired_deltas.get(resource, 0)
+                total_usage = current_usages[resource] - expired_reservations
+                # A negative quota limit means infinite
+                if current_limits[resource] < 0:
+                    LOG.debug(("Resource %(resource)s has unlimited quota "
+                               "limit. It is possible to allocate %(delta)s "
+                               "items."), {'resource': resource,
+                                           'delta': deltas[resource]})
+                    continue
+                res_headroom = current_limits[resource] - total_usage
+                LOG.debug(("Attempting to reserve %(delta)d items for "
+                           "resource %(resource)s. Total usage: %(total)d; "
+                           "quota limit: %(limit)d; headroom:%(headroom)d"),
+                          {'resource': resource,
+                           'delta': deltas[resource],
+                           'total': total_usage,
+                           'limit': current_limits[resource],
+                           'headroom': res_headroom})
+                if res_headroom < deltas[resource]:
+                    resources_over_limit.append(resource)
+                if expired_reservations:
+                    self._handle_expired_reservations(
+                        context, tenant_id, resource, expired_reservations)
+
+            if resources_over_limit:
+                raise exceptions.OverQuota(overs=sorted(resources_over_limit))
+            # Success, store the reservation
+            # TODO(salv-orlando): Make expiration time configurable
+            return quota_api.create_reservation(
+                context, tenant_id, deltas)
+
+    def commit_reservation(self, context, reservation_id):
+        # Do not mark resource usage as dirty. If a reservation is committed,
+        # then the releveant resources have been created. Usage data for these
+        # resources has therefore already been marked dirty.
+        quota_api.remove_reservation(context, reservation_id,
+                                     set_dirty=False)
+
+    def cancel_reservation(self, context, reservation_id):
+        # Mark resource usage as dirty so the next time both actual resources
+        # used and reserved will be recalculated
+        quota_api.remove_reservation(context, reservation_id,
+                                     set_dirty=True)
+
     def limit_check(self, context, tenant_id, resources, values):
         """Check simple quota limits.
 

neutron/db/quota/models.py

@@ -13,12 +13,33 @@
 #    under the License.
 
 import sqlalchemy as sa
+from sqlalchemy import orm
 from sqlalchemy import sql
 
 from neutron.db import model_base
 from neutron.db import models_v2
 
 
+class ResourceDelta(model_base.BASEV2):
+    resource = sa.Column(sa.String(255), primary_key=True)
+    reservation_id = sa.Column(sa.String(36),
+                               sa.ForeignKey('reservations.id',
+                                             ondelete='CASCADE'),
+                               primary_key=True,
+                               nullable=False)
+    # Requested amount of resource
+    amount = sa.Column(sa.Integer)
+
+
+class Reservation(model_base.BASEV2, models_v2.HasId):
+    tenant_id = sa.Column(sa.String(255))
+    expiration = sa.Column(sa.DateTime())
+    resource_deltas = orm.relationship(ResourceDelta,
+                                       backref='reservation',
+                                       lazy="joined",
+                                       cascade='all, delete-orphan')
+
+
 class Quota(model_base.BASEV2, models_v2.HasId, models_v2.HasTenant):
     """Represent a single quota override for a tenant.
 

neutron/quota/__init__.py

@@ -24,6 +24,7 @@ import six
 import webob
 
 from neutron.common import exceptions
+from neutron.db.quota import api as quota_api
 from neutron.i18n import _LI, _LW
 from neutron.quota import resource_registry
 
@@ -152,6 +153,33 @@ class ConfDriver(object):
         msg = _('Access to this resource was denied.')
         raise webob.exc.HTTPForbidden(msg)
 
+    def make_reservation(self, context, tenant_id, resources, deltas, plugin):
+        """This driver does not support reservations.
+
+        This routine is provided for backward compatibility purposes with
+        the API controllers which have now been adapted to make reservations
+        rather than counting resources and checking limits - as this
+        routine ultimately does.
+        """
+        for resource in deltas.keys():
+            count = QUOTAS.count(context, resource, plugin, tenant_id)
+            total_use = deltas.get(resource, 0) + count
+            deltas[resource] = total_use
+
+        self.limit_check(
+            context,
+            tenant_id,
+            resource_registry.get_all_resources(),
+            deltas)
+        # return a fake reservation - the REST controller expects it
+        return quota_api.ReservationInfo('fake', None, None, None)
+
+    def commit_reservation(self, context, reservation_id):
+        """Tnis is a noop as this driver does not support reservations."""
+
+    def cancel_reservation(self, context, reservation_id):
+        """Tnis is a noop as this driver does not support reservations."""
+
 
 class QuotaEngine(object):
     """Represent the set of recognized quotas."""
@@ -210,6 +238,39 @@ class QuotaEngine(object):
 
         return res.count(context, *args, **kwargs)
 
+    def make_reservation(self, context, tenant_id, deltas, plugin):
+        # Verify that resources are managed by the quota engine
+        # Ensure no value is less than zero
+        unders = [key for key, val in deltas.items() if val < 0]
+        if unders:
+            raise exceptions.InvalidQuotaValue(unders=sorted(unders))
+
+        requested_resources = set(deltas.keys())
+        all_resources = resource_registry.get_all_resources()
+        managed_resources = set([res for res in all_resources.keys()
+                                 if res in requested_resources])
+        # Make sure we accounted for all of them...
+        unknown_resources = requested_resources - managed_resources
+
+        if unknown_resources:
+            raise exceptions.QuotaResourceUnknown(
+                unknown=sorted(unknown_resources))
+        # FIXME(salv-orlando): There should be no reason for sending all the
+        # resource in the registry to the quota driver, but as other driver
+        # APIs request them, this will be sorted out with a different patch.
+        return self.get_driver().make_reservation(
+            context,
+            tenant_id,
+            all_resources,
+            deltas,
+            plugin)
+
+    def commit_reservation(self, context, reservation_id):
+        self.get_driver().commit_reservation(context, reservation_id)
+
+    def cancel_reservation(self, context, reservation_id):
+        self.get_driver().cancel_reservation(context, reservation_id)
+
     def limit_check(self, context, tenant_id, **values):
         """Check simple quota limits.
 
@@ -232,6 +293,7 @@ class QuotaEngine(object):
         :param tenant_id: Tenant for which the quota limit is being checked
         :param values: Dict specifying requested deltas for each resource
         """
+        # TODO(salv-orlando): Deprecate calls to this API
         # Verify that resources are managed by the quota engine
         requested_resources = set(values.keys())
         managed_resources = set([res for res in

neutron/quota/resource.py

@@ -208,14 +208,15 @@ class TrackedResource(BaseResource):
         max_retries=db_api.MAX_RETRIES,
         exception_checker=lambda exc:
         isinstance(exc, oslo_db_exception.DBDuplicateEntry))
-    def _set_quota_usage(self, context, tenant_id, in_use):
-        return quota_api.set_quota_usage(context, self.name,
-                                         tenant_id, in_use=in_use)
+    def _set_quota_usage(self, context, tenant_id, in_use, reserved):
+        return quota_api.set_quota_usage(context, self.name, tenant_id,
+                                         in_use=in_use, reserved=reserved)
 
-    def _resync(self, context, tenant_id, in_use):
+    def _resync(self, context, tenant_id, in_use, reserved):
         # Update quota usage
         usage_info = self._set_quota_usage(
-            context, tenant_id, in_use=in_use)
+            context, tenant_id, in_use, reserved)
+
         self._dirty_tenants.discard(tenant_id)
         self._out_of_sync_tenants.discard(tenant_id)
         LOG.debug(("Unset dirty status for tenant:%(tenant_id)s on "
@@ -231,40 +232,62 @@ class TrackedResource(BaseResource):
                   {'tenant_id': tenant_id, 'resource': self.name})
         in_use = context.session.query(self._model_class).filter_by(
             tenant_id=tenant_id).count()
+        reservations = quota_api.get_reservations_for_resources(
+            context, tenant_id, [self.name])
+        reserved = reservations.get(self.name, 0)
         # Update quota usage
-        return self._resync(context, tenant_id, in_use)
+        return self._resync(context, tenant_id, in_use, reserved)
 
     def count(self, context, _plugin, tenant_id, resync_usage=False):
-        """Return the current usage count for the resource."""
-        # Load current usage data
+        """Return the current usage count for the resource.
+
+        This method will fetch the information from resource usage data,
+        unless usage data are marked as "dirty", in which case both used and
+        reserved resource are explicitly counted.
+
+        The _plugin and _resource parameters are unused but kept for
+        compatibility with the signature of the count method for
+        CountableResource instances.
+        """
+        # Load current usage data, setting a row-level lock on the DB
         usage_info = quota_api.get_quota_usage_by_resource_and_tenant(
-            context, self.name, tenant_id)
+            context, self.name, tenant_id, lock_for_update=True)
         # If dirty or missing, calculate actual resource usage querying
         # the database and set/create usage info data
         # NOTE: this routine "trusts" usage counters at service startup. This
         # assumption is generally valid, but if the database is tampered with,
         # or if data migrations do not take care of usage counters, the
         # assumption will not hold anymore
-        if (tenant_id in self._dirty_tenants or not usage_info
-            or usage_info.dirty):
+        if (tenant_id in self._dirty_tenants or
+            not usage_info or usage_info.dirty):
             LOG.debug(("Usage tracker for resource:%(resource)s and tenant:"
                        "%(tenant_id)s is out of sync, need to count used "
                        "quota"), {'resource': self.name,
                                   'tenant_id': tenant_id})
             in_use = context.session.query(self._model_class).filter_by(
                 tenant_id=tenant_id).count()
+            reservations = quota_api.get_reservations_for_resources(
+                context, tenant_id, [self.name])
+            reserved = reservations.get(self.name, 0)
+
             # Update quota usage, if requested (by default do not do that, as
             # typically one counts before adding a record, and that would mark
             # the usage counter as dirty again)
             if resync_usage or not usage_info:
-                usage_info = self._resync(context, tenant_id, in_use)
+                usage_info = self._resync(context, tenant_id,
+                                          in_use, reserved)
             else:
                 usage_info = quota_api.QuotaUsageInfo(usage_info.resource,
                                                       usage_info.tenant_id,
                                                       in_use,
-                                                      usage_info.reserved,
+                                                      reserved,
                                                       usage_info.dirty)
 
+            LOG.debug(("Quota usage for %(resource)s was recalculated. "
+                       "Used quota:%(used)d; Reserved quota:%(reserved)d"),
+                      {'resource': self.name,
+                       'used': usage_info.used,
+                       'reserved': usage_info.reserved})
         return usage_info.total
 
     def register_events(self):

neutron/quota/resource_registry.py

@@ -65,7 +65,7 @@ def set_resources_dirty(context):
         return
 
     for res in get_all_resources().values():
-        with context.session.begin():
+        with context.session.begin(subtransactions=True):
             if is_tracked(res.name) and res.dirty:
                 res.mark_dirty(context, nested=True)
 

neutron/tests/unit/db/quota/test_api.py

@@ -12,6 +12,10 @@
 #    License for the specific language governing permissions and limitations
 #    under the License.
 
+import datetime
+
+import mock
+
 from neutron import context
 from neutron.db.quota import api as quota_api
 from neutron.tests.unit import testlib_api
@@ -24,6 +28,12 @@ class TestQuotaDbApi(testlib_api.SqlTestCaseLight):
         self.context = context.Context('Gonzalo', self.tenant_id,
                                        is_admin=False, is_advsvc=False)
 
+    def _create_reservation(self, resource_deltas,
+                            tenant_id=None, expiration=None):
+        tenant_id = tenant_id or self.tenant_id
+        return quota_api.create_reservation(
+            self.context, tenant_id, resource_deltas, expiration)
+
     def _create_quota_usage(self, resource, used, reserved, tenant_id=None):
         tenant_id = tenant_id or self.tenant_id
         return quota_api.set_quota_usage(
@@ -203,6 +213,125 @@ class TestQuotaDbApi(testlib_api.SqlTestCaseLight):
         self.assertIsNone(quota_api.get_quota_usage_by_resource_and_tenant(
             self.context, 'goals', self.tenant_id))
 
+    def _verify_reserved_resources(self, expected, actual):
+        for (resource, delta) in actual.items():
+            self.assertIn(resource, expected)
+            self.assertEqual(delta, expected[resource])
+            del expected[resource]
+        self.assertFalse(expected)
+
+    def test_create_reservation(self):
+        resources = {'goals': 2, 'assists': 1}
+        resv = self._create_reservation(resources)
+        self.assertEqual(self.tenant_id, resv.tenant_id)
+        self._verify_reserved_resources(resources, resv.deltas)
+
+    def test_create_reservation_with_expirtion(self):
+        resources = {'goals': 2, 'assists': 1}
+        exp_date = datetime.datetime(2016, 3, 31, 14, 30)
+        resv = self._create_reservation(resources, expiration=exp_date)
+        self.assertEqual(self.tenant_id, resv.tenant_id)
+        self.assertEqual(exp_date, resv.expiration)
+        self._verify_reserved_resources(resources, resv.deltas)
+
+    def _test_remove_reservation(self, set_dirty):
+        resources = {'goals': 2, 'assists': 1}
+        resv = self._create_reservation(resources)
+        self.assertEqual(1, quota_api.remove_reservation(
+            self.context, resv.reservation_id, set_dirty=set_dirty))
+
+    def test_remove_reservation(self):
+        self._test_remove_reservation(False)
+
+    def test_remove_reservation_and_set_dirty(self):
+        routine = 'neutron.db.quota.api.set_resources_quota_usage_dirty'
+        with mock.patch(routine) as mock_routine:
+            self._test_remove_reservation(False)
+        mock_routine.assert_called_once_with(
+            self.context, mock.ANY, self.tenant_id)
+
+    def test_remove_non_existent_reservation(self):
+        self.assertIsNone(quota_api.remove_reservation(self.context, 'meh'))
+
+    def _get_reservations_for_resource_helper(self):
+        # create three reservation, 1 expired
+        resources_1 = {'goals': 2, 'assists': 1}
+        resources_2 = {'goals': 3, 'bookings': 1}
+        resources_3 = {'bookings': 2, 'assists': 2}
+        exp_date_1 = datetime.datetime(2016, 3, 31, 14, 30)
+        exp_date_2 = datetime.datetime(2015, 3, 31, 14, 30)
+        self._create_reservation(resources_1, expiration=exp_date_1)
+        self._create_reservation(resources_2, expiration=exp_date_1)
+        self._create_reservation(resources_3, expiration=exp_date_2)
+
+    def test_get_reservations_for_resources(self):
+        with mock.patch('neutron.db.quota.api.utcnow') as mock_utcnow:
+            self._get_reservations_for_resource_helper()
+            mock_utcnow.return_value = datetime.datetime(
+                2015, 5, 20, 0, 0)
+            deltas = quota_api.get_reservations_for_resources(
+                self.context, self.tenant_id, ['goals', 'assists', 'bookings'])
+            self.assertIn('goals', deltas)
+            self.assertEqual(5, deltas['goals'])
+            self.assertIn('assists', deltas)
+            self.assertEqual(1, deltas['assists'])
+            self.assertIn('bookings', deltas)
+            self.assertEqual(1, deltas['bookings'])
+            self.assertEqual(3, len(deltas))
+
+    def test_get_expired_reservations_for_resources(self):
+        with mock.patch('neutron.db.quota.api.utcnow') as mock_utcnow:
+            mock_utcnow.return_value = datetime.datetime(
+                2015, 5, 20, 0, 0)
+            self._get_reservations_for_resource_helper()
+            deltas = quota_api.get_reservations_for_resources(
+                self.context, self.tenant_id,
+                ['goals', 'assists', 'bookings'],
+                expired=True)
+            self.assertIn('assists', deltas)
+            self.assertEqual(2, deltas['assists'])
+            self.assertIn('bookings', deltas)
+            self.assertEqual(2, deltas['bookings'])
+            self.assertEqual(2, len(deltas))
+
+    def test_get_reservation_for_resources_with_empty_list(self):
+        self.assertIsNone(quota_api.get_reservations_for_resources(
+            self.context, self.tenant_id, []))
+
+    def test_remove_expired_reservations(self):
+        with mock.patch('neutron.db.quota.api.utcnow') as mock_utcnow:
+            mock_utcnow.return_value = datetime.datetime(
+                2015, 5, 20, 0, 0)
+            resources = {'goals': 2, 'assists': 1}
+            exp_date_1 = datetime.datetime(2016, 3, 31, 14, 30)
+            resv_1 = self._create_reservation(resources, expiration=exp_date_1)
+            exp_date_2 = datetime.datetime(2015, 3, 31, 14, 30)
+            resv_2 = self._create_reservation(resources, expiration=exp_date_2)
+            self.assertEqual(1, quota_api.remove_expired_reservations(
+                self.context, self.tenant_id))
+            self.assertIsNone(quota_api.get_reservation(
+                self.context, resv_2.reservation_id))
+            self.assertIsNotNone(quota_api.get_reservation(
+                self.context, resv_1.reservation_id))
+
+    def test_remove_expired_reservations_no_tenant(self):
+        with mock.patch('neutron.db.quota.api.utcnow') as mock_utcnow:
+            mock_utcnow.return_value = datetime.datetime(
+                2015, 5, 20, 0, 0)
+            resources = {'goals': 2, 'assists': 1}
+            exp_date_1 = datetime.datetime(2014, 3, 31, 14, 30)
+            resv_1 = self._create_reservation(resources, expiration=exp_date_1)
+            exp_date_2 = datetime.datetime(2015, 3, 31, 14, 30)
+            resv_2 = self._create_reservation(resources,
+                                              expiration=exp_date_2,
+                                              tenant_id='Callejon')
+            self.assertEqual(2, quota_api.remove_expired_reservations(
+                self.context))
+            self.assertIsNone(quota_api.get_reservation(
+                self.context, resv_2.reservation_id))
+            self.assertIsNone(quota_api.get_reservation(
+                self.context, resv_1.reservation_id))
+
 
 class TestQuotaDbApiAdminContext(TestQuotaDbApi):
 

neutron/tests/unit/db/quota/test_driver.py

@@ -27,16 +27,22 @@ class FakePlugin(base_plugin.NeutronDbPluginV2, driver.DbQuotaDriver):
 class TestResource(object):
     """Describe a test resource for quota checking."""
 
-    def __init__(self, name, default):
+    def __init__(self, name, default, fake_count=0):
         self.name = name
         self.quota = default
+        self.fake_count = fake_count
 
     @property
     def default(self):
         return self.quota
 
+    def count(self, *args, **kwargs):
+        return self.fake_count
+
+
 PROJECT = 'prj_test'
 RESOURCE = 'res_test'
+ALT_RESOURCE = 'res_test_meh'
 
 
 class TestDbQuotaDriver(testlib_api.SqlTestCase):
@@ -132,3 +138,63 @@ class TestDbQuotaDriver(testlib_api.SqlTestCase):
         self.assertRaises(exceptions.InvalidQuotaValue,
                           self.plugin.limit_check, context.get_admin_context(),
                           PROJECT, resources, values)
+
+    def _test_make_reservation_success(self, quota_driver,
+                                       resource_name, deltas):
+        resources = {resource_name: TestResource(resource_name, 2)}
+        self.plugin.update_quota_limit(self.context, PROJECT, resource_name, 2)
+        reservation = quota_driver.make_reservation(
+            self.context,
+            self.context.tenant_id,
+            resources,
+            deltas,
+            self.plugin)
+        self.assertIn(resource_name, reservation.deltas)
+        self.assertEqual(deltas[resource_name],
+                         reservation.deltas[resource_name])
+        self.assertEqual(self.context.tenant_id,
+                         reservation.tenant_id)
+
+    def test_make_reservation_single_resource(self):
+        quota_driver = driver.DbQuotaDriver()
+        self._test_make_reservation_success(
+            quota_driver, RESOURCE, {RESOURCE: 1})
+
+    def test_make_reservation_fill_quota(self):
+        quota_driver = driver.DbQuotaDriver()
+        self._test_make_reservation_success(
+            quota_driver, RESOURCE, {RESOURCE: 2})
+
+    def test_make_reservation_multiple_resources(self):
+        quota_driver = driver.DbQuotaDriver()
+        resources = {RESOURCE: TestResource(RESOURCE, 2),
+                     ALT_RESOURCE: TestResource(ALT_RESOURCE, 2)}
+        deltas = {RESOURCE: 1, ALT_RESOURCE: 2}
+        self.plugin.update_quota_limit(self.context, PROJECT, RESOURCE, 2)
+        self.plugin.update_quota_limit(self.context, PROJECT, ALT_RESOURCE, 2)
+        reservation = quota_driver.make_reservation(
+            self.context,
+            self.context.tenant_id,
+            resources,
+            deltas,
+            self.plugin)
+        self.assertIn(RESOURCE, reservation.deltas)
+        self.assertIn(ALT_RESOURCE, reservation.deltas)
+        self.assertEqual(1, reservation.deltas[RESOURCE])
+        self.assertEqual(2, reservation.deltas[ALT_RESOURCE])
+        self.assertEqual(self.context.tenant_id,
+                         reservation.tenant_id)
+
+    def test_make_reservation_over_quota_fails(self):
+        quota_driver = driver.DbQuotaDriver()
+        resources = {RESOURCE: TestResource(RESOURCE, 2,
+                                            fake_count=2)}
+        deltas = {RESOURCE: 1}
+        self.plugin.update_quota_limit(self.context, PROJECT, RESOURCE, 2)
+        self.assertRaises(exceptions.OverQuota,
+                          quota_driver.make_reservation,
+                          self.context,
+                          self.context.tenant_id,
+                          resources,
+                          deltas,
+                          self.plugin)

neutron/tests/unit/extensions/test_quotasv2.py

@@ -344,6 +344,24 @@ class QuotaExtensionDbTestCase(QuotaExtensionTestCase):
                            extra_environ=env, expect_errors=True)
         self.assertEqual(400, res.status_int)
 
+    def test_make_reservation_resource_unknown_raises(self):
+        tenant_id = 'tenant_id1'
+        self.assertRaises(exceptions.QuotaResourceUnknown,
+                          quota.QUOTAS.make_reservation,
+                          context.get_admin_context(load_admin_roles=False),
+                          tenant_id,
+                          {'foobar': 1},
+                          plugin=None)
+
+    def test_make_reservation_negative_delta_raises(self):
+        tenant_id = 'tenant_id1'
+        self.assertRaises(exceptions.InvalidQuotaValue,
+                          quota.QUOTAS.make_reservation,
+                          context.get_admin_context(load_admin_roles=False),
+                          tenant_id,
+                          {'network': -1},
+                          plugin=None)
+
 
 class QuotaExtensionCfgTestCase(QuotaExtensionTestCase):
     fmt = 'json'

neutron/tests/unit/quota/test_resource.py

@@ -165,7 +165,8 @@ class TestTrackedResource(testlib_api.SqlTestCaseLight):
             res.count(self.context, None, self.tenant_id,
                       resync_usage=True)
             mock_set_quota_usage.assert_called_once_with(
-                self.context, self.resource, self.tenant_id, in_use=2)
+                self.context, self.resource, self.tenant_id,
+                reserved=0, in_use=2)
 
     def test_count_with_dirty_true_no_usage_info(self):
         res = self._create_resource()
@@ -184,7 +185,8 @@ class TestTrackedResource(testlib_api.SqlTestCaseLight):
                                             self.tenant_id)
             res.count(self.context, None, self.tenant_id, resync_usage=True)
             mock_set_quota_usage.assert_called_once_with(
-                self.context, self.resource, self.tenant_id, in_use=2)
+                self.context, self.resource, self.tenant_id,
+                reserved=0, in_use=2)
 
     def test_add_delete_data_triggers_event(self):
         res = self._create_resource()
@@ -251,4 +253,5 @@ class TestTrackedResource(testlib_api.SqlTestCaseLight):
             # and now it should be in sync
             self.assertNotIn(self.tenant_id, res._out_of_sync_tenants)
             mock_set_quota_usage.assert_called_once_with(
-                self.context, self.resource, self.tenant_id, in_use=2)
+                self.context, self.resource, self.tenant_id,
+                reserved=0, in_use=2)