Hibernate version:2.1

1) I have a table of 100 Millions lines, does it make sens to map this table with hibernate ? what are the must to know when dealing with this kind of tables ? how to limit the caches size for long run ?

2) mapping question : in a legacy table, I have the following columns

countryId
branchName
dataCol

I have to map countryId to class Country with table T_COUNTRY
and countryId + branchName to Branch with table T_BRANCH

the composite id countryId + branchName uses countryId again thus the trouble : I should mark Branch as insert="false" and update="false" !

what is the right way to model this situation so the insert and update become possible for branch ?

TIA

Qiang