H2 does not support clob/blob (text) indexes on non-memory databases (files)
I changed id to varchar(33). If this is an md5 string the length should be enough, other wise we can increase it.

In addition, when reusing an existing (file) cache, create index failed because it already exists
Merge pull request #3 from AKSW/cache_schema

H2 does not support clob/blob (text) indexes on non-memory databases