I guess we could argue if that's good or not, but that's how it is.

Yes, that was my thinking, having a grouping sub-namespace to such specific settings, e.g. "hibernate.search. myindex.infinispan.write_metadata_async". That'd convey that it an index-scoped setting, specific to ISPN. Anyways, good to know how it is, I guess I had done it as described

I will never be able to test for that.

That convinces me.