---
fixes:
  - |
    Used "passive_deletes=True" in the configuration of relationships in
    SQLAlchemy models. This improves deletion of graphs of related objects
    stored in DB because dependent objects don't get loaded prior to
    deletion which also reduces the memory requirement on the system.
    More about using this flag can be found at:
    http://docs.sqlalchemy.org/en/latest/orm/collections.html#using-passive-deletes