---
prelude: >
  - **Experimental** zero-downtime database upgrade using an
    expand-migrate-contract series of operations is available.
upgrade:
  - |
    The database migration engine used by Glance for database upgrades has been
    changed from *SQLAlchemy Migrate* to *Alembic* in this release.

    * This has necessitated a change in the location and naming convention for
      migration scripts.  Developers, operators, and DevOps are strongly
      encouraged to read through the `Database Management`_ section of the
      Glance documentation for details of the changes introduced in the Ocata
      release.  Here's a brief summary of the changes:

      - All the ``glance manage db`` commands are changed appropriately to use
        Alembic to perform operations such as ``version``, ``upgrade``,
        ``sync`` and ``version_control``.  Hence, the "old-style" migration
        scripts will no longer work with the Ocata glance manage db commands.

      - Database versions are no longer numerical.  Instead, they are the
        *revision ID* of the last migration applied on the database.

        * For example, the Liberty migration, which was version ``42`` under
          the old system, will now appear as ``liberty``.  The Mitaka
          migrations ``43`` and ``44`` appear as ``mitaka01`` and ``mitaka02``,
          respectively.

    * The change in migration engine has been undertaken in order to enable
      zero-downtime database upgrades, which are part of the effort to
      implement rolling upgrades for Glance (scheduled for the Pike release).

      - A preview of zero-downtime database upgrades is available in this
        release, but it is **experimental** and **not supported for production
        systems**.  Please consult the `Database Management`_ section of the
        Glance documentation for details.

    .. _`Database Management`: http://docs.openstack.org/developer/glance/db.html