Is there a better name for Metadata? Like FileMetadata maybe?

Better FileMetadata or maybe FileHeader.

FileMetadata is better I think.

Where is ispn-cache-default-conf.xml used? For tests only? If not: is it possible to use a programmatic version instead and what is "It's a movie cache"?

Yes in tests only so far. However it can be used as a provided default configuration. I will send maybe question to infinispan group about best configuration parameters. "It's a movie cache" it's the name for cache configured in ispn-cache-default-conf.xml. In tests in this cache are stored indexes for entity Movie. Indexes for all other entities are stored in default HSInfinispanCache.

If it's only used in tests, let's move this resource out of the main sources and to the test sources.

If we plan to be some kind of default inside HSearch, then the programmatic approach is better I think if it's possible.