OGM is ongoing some refactoring around the associations mapping to be able to provide similar locking and isolation experience as when using a traditional database. An association is mapped as tuples, which represent the columns on the relational database (the association table); So each association is identified by : [tableName - FKcolumnName - FKcolumnValue] and the value should "point to" the tuples. In case the association is represented by a List of Set, then the association table will have primary keys which prevents duplication of entries: - this set of primary keys is going to be the key of the FineGrainedLockingAtomicMap[1] - the elements of the touple not being part of the PK will be the value used for the same FGLAM - by the semantics of FGLAM, this means we can effectively modify the elements which are identified by the PK, and acquire a lock only on those "rows", effectively implementing the desired locking. - identifying which elements are part of the PK and which are not can be done at boot time, when figuring the "schema" of the database; it depends on the kind of relation. In case we're mapping a Bag, then it seems that we have no alternative than to lock the whole set of values: as implementation we could use the existing AtomicMap API from Infinispan. one new thought: - the core reference suggests that adding to a Bag can be quite efficient as it doesn't need a return value. thinking about that, it seems possible that the Bag modification doesn't need an eager lock. In all cases, we're going to use custom types to represent the keys, so that we can be flexible in changing it and write custom Externalizers. Basically, it will take some more time before this is implemented; some drafts of the previous ideas (now deprecated) can be found at: https://github.com/emmanuelbernard/hibernate-ogm/tree/atomicmap [1] - as https://issues.jboss.org/browse/ISPN-1115 Cheers, Sanne