2.2.1 is a minor release that fixes a bug in viewCleanup() where indexes were not properly cleaned up (#2162).
No data will be lost if you upgrade from 2.2.0 to 2.2.1; you can continue using persistent map/reduce like you were before. This release does not contain a database migration.
This release also updates our dependencies, such as lie v2.7.4, which contains some performance improvements since the last release.