One of the changes between JCR 1.0 and JCR 2.0 is the definition of nt:frozenNode. In JCR 1.0 the node type extends from mix:referenceable, while in JCR 2.0 it does not anymore.
Oak currently uses a nt:frozenNode definition that extends from mix:referenceable. This adds quite a bit of overhead because each node written under a JCR version gets a jcr:uuid, which is indexed by default.
The proposal is to remove the supertype "mix:referenceable" from nt:frozenNode.
Removing this supertype, the frozenNodes wouldn't have a "jcr:uuid" field, which at the end is not used, and allows to reduce the size of the index.