---
upgrade:
  - |
    Experimental support for thread pooling of DB API calls has been removed.
    This feature was first introduced in the 2014.2 (Juno) release but has not
    graduated to fully-supported status since nor was it being used for any
    API DB calls. The ``[oslo_db] use_tpool`` config option used to enable
    this feature will now be ignored by nova.