Version v0.40 of Metabase is no longer supported. Check out the docs for the current stable version, Metabase v0.63.
What’s H2?
H2 is a lightweight, in-memory database; it’s perfect for getting spun up quickly, but not so good for long-term usage. By default, Metabase uses H2 to store its internal data. If you want to run Metabase in production, we recommend that you migrate off H2.
Read docs for other versions of Metabase.