I don’t know if the JPA TCK has anything to say about the allocationSize, but the spec document says:
The amount
to increment by when
allocating numbers
from the generator/sequence.
What should hbm2ddl update do in such a case where increment size > allocation size?
This is a pretty special use case for which it IMO is ok to require a user to write/configure a custom optimizer. I don’t think it is very common to intentionally introduce gaps in sequence values. Hope you understand this.