The DataCacheStoreManager.transformToVersionSafePCDatas() line 261. This method should call either cache.containsAll() or cache.getAll(). The current implementation makes one call to the cache for each element in the collection.
The AbstractDataCache.putAllInternal() method suffers from the same issues. This is OK becuase it can be overwritten in a plugin. But I am thinking that maybe someone from the openjpa developer community might want to fix that in there too. That way the base class could actually be used as a base class to write other L2 cache plugins. F