glance/doc/source/admin/db.rst

Database Management

The default metadata driver for Glance uses SQLAlchemy, which implies there exists a backend database which must be managed. The glance-manage binary provides a set of commands for making this easier.

The commands should be executed as a subcommand of 'db':

glance-manage db <cmd> <args>

Note

In the Ocata release (14.0.0), the database migration engine was changed from SQLAlchemy Migrate to Alembic. This necessitated some changes in the glance-manage tool. While the user interface has been kept as similar as possible, the glance-manage tool included with the Ocata and more recent releases is incompatible with the "legacy" tool. If you are consulting these documents for information about the glance-manage tool in the Newton or earlier releases, please see the legacy-database-management page.

Migration Scripts

The migration scripts are stored in the directory: glance/db/sqlalchemy/alembic_migrations/versions

As mentioned above, these scripts utilize the Alembic migration engine, which was first introduced in the Ocata release. All database migrations up through the Liberty release are consolidated into one Alembic migration script named liberty_initial. Mitaka migrations are retained, but have been rewritten for Alembic and named using the new naming convention.

A fresh Glance installation will apply the following migrations:

• liberty-initial
• mitaka01
• mitaka02
• ocata01

Note

The "old-style" migration scripts have been retained in their current directory in the Ocata release so that interested operators can correlate them with the new migrations. This directory will be removed in future releases.

In particular, the "old-style" script for the Ocata migration, 045_add_visibility.py is retained for operators who are conversant in SQLAlchemy Migrate and are interested in comparing it with a "new-style" Alembic migration script. The Alembic script, which is the one actually used to do the upgrade to Ocata, is ocata01_add_visibility_remove_is_public.py.

Sync the Database

glance-manage db sync [VERSION]

Place an existing database under migration control and upgrade it to the specified VERSION or to the latest migration level if VERSION is not specified.

Note

Prior to Ocata release the database version was a numeric value. For example: for the Newton release, the latest migration level was 44. Starting with Ocata, database version is a revision name corresponding to the latest migration included in the release. For the Ocata release, there is only one database migration and it is identified by revision ocata01. So, the database version for Ocata release is ocata01.

This naming convention will change slightly with the introduction of zero-downtime upgrades, which is EXPERIMENTAL in Ocata, but is projected to be the official upgrade method beginning with the Pike release. See zero-downtime for more information.

Determining the Database Version

glance-manage db version

This will print the current migration level of a Glance database.

Upgrading an Existing Database

glance-manage db upgrade [VERSION]

This will take an existing database and upgrade it to the specified VERSION.

Downgrading an Existing Database

Downgrading an existing database is NOT SUPPORTED.

Upgrades involve complex operations and can fail. Before attempting any upgrade, you should make a full database backup of your production data. As of the OpenStack Kilo release (April 2013), database downgrades are not supported, and the only method available to get back to a prior database version is to restore from backup.