BMP - how to cache?

Hi!
before we started in J2EE I used Castor as my o/r mapping tool. It caches the object nicely so the load on the database was low.
Now we started using J2EE, first using CMP for our entity beans (J2EE server in the SEAS 8 PE) with the built in JDO implementation. Here my first question: Does this implementation (or any JDO implementation) also cache the obejcts?
For a new project we have to use BMP for the entity beans because we have to versioning all updated in the database (an setXXX() on an entity bean creates a new row (=version) for the object in the database). We directly coded the sql statements in the bean (in ejbStore, ejbLoad, ...).
Any idea how we can cache objectes in our BMP approach? Should we also use JDO here?
Thank you for any comments about this in advance....

W.g. we store information about orders in the databse which are not often changed, this information can be cached by the persistent layer. But when I access the db directly with sql statements (db is Oracle here), be have two db access everytime we access an order: One for the pk search and one for getting the data (when using value objects).

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hello
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