Fix quota double-spending with uniqueness-constraint

We introduce a uniqueness-constraint to avoid duplicate entries in the
quota_usages table. For introducing this, we have to delete the
duplicates already present and the soft-deleted reservations referencing
duplicate entries.

Things learned here: Do not use _and_ statement, as it will replace it
with an expression-object. Also we first tried a rank query, but now use
a join.

Author: fwiesel

cinder/db/sqlalchemy/migrate_repo/versions/119_fix_quota_double_spending.py

@@ -0,0 +1,77 @@
+# Copyright 2018 SAP SE
+#
+# 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.
+
+from migrate.changeset.constraint import UniqueConstraint
+from sqlalchemy import MetaData, Table
+from sqlalchemy import select, join, and_
+from oslo_log import log as logging
+
+LOG = logging.getLogger(__name__)
+META = MetaData()
+
+
+def quota_usages_table(migrate_engine):
+    global META
+    META.bind = migrate_engine
+
+    return Table('quota_usages', META, autoload=True)
+
+
+def _build_constraint(migrate_engine, quota_usages=None):
+    if quota_usages is None:
+        quota_usages = quota_usages_table(migrate_engine)
+    return UniqueConstraint(
+        'project_id', 'resource', 'deleted',
+        table=quota_usages,
+    )
+
+
+def upgrade(migrate_engine):
+    global META
+    quota_usages = quota_usages_table(migrate_engine)
+
+    qu1 = quota_usages.alias('qu1')
+    qu2 = quota_usages.alias('qu2')
+    duplicates = select([qu1.c.id]).select_from(join(
+        qu1, qu2,
+        onclause=and_(
+            qu1.c.project_id == qu2.c.project_id,
+            qu1.c.resource == qu2.c.resource,
+            qu1.c.deleted == qu2.c.deleted,
+        )
+    )).where(
+        qu1.c.id > qu2.c.id
+    )
+
+    reservations = Table('reservations', META, autoload=True)
+
+    query = reservations.delete(
+        whereclause=and_(reservations.c.usage_id.in_(duplicates),
+                         reservations.c.deleted)
+    )
+
+    migrate_engine.execute(query)
+
+    query = quota_usages.delete(
+        whereclause=quota_usages.c.id.in_(duplicates)
+    )
+
+    migrate_engine.execute(query)
+    cons = _build_constraint(migrate_engine, quota_usages=quota_usages)
+    cons.create()
+
+
+def downgrade(migrate_engine):
+    cons = _build_constraint(migrate_engine)
+    cons.drop()