'''For people who have already upgraded their database to version 22, this requires manual intervention on the database.'''
You can either remove the `cache` table and re-create it by hand:
{{{
DROP TABLE cache;
CREATE TABLE cache ( id text PRIMARY KEY, generation int );
}}}
(for SQLite; or the equivalent for your database)
Or you can downgrade the database version, drop the `cache` table, and upgrade again:
{{{
UPDATE system SET value=21 WHERE name='database_version';
DROP TABLE cache;
trac-admin $TRAC_ENV upgrade
}}}
Closes #8197.
