---
upgrade:
  - |
    oslo.db now logs a warning when the connection URL does not
    explicitly mention a driver. The default driver is still used, but
    in some cases, such as MySQL, the default is incompatible with the
    concurrency library eventlet.
  - |
    It is strongly recommended to use the `PyMySQL
    <https://pypi.python.org/pypi/PyMySQL>`__ driver when connecting
    to a MySQL-compatible database to ensure the best compatibility
    with the concurrency library eventlet. To use PyMySQL, ensure the
    connection URL is specified with ``mysql+pymysql://`` as the
    scheme.