trunk can be checked out as follows
svn co https://datanucleus.svn.sourceforge.net/svnroot/datanucleus/platform/cache/trunk cache
datanucleus-cache is downloadable as following
datanucleus-cache is dependent on the following packages of software. Click on the name to go to the home page for that software to download it.
|datanucleus-core||3.0+||Provides logging, localisation, and other framework facilities for DataNucleus.||Yes|
|ehcache||1.1+||EHCache caching||Yes if using EHCache|
|Oracle Coherence||Oracle Coherence caching||Yes, if using Coherence|
|oscache||2.1||OSCache caching||Yes, is using OSCache|
|swarmcache||1.0RC2||SwarmCache caching||Yes, if using SwarmCache|
|net.sf.jsr107cache||1.1||JCache caching||Yes, if using JCache|
|spymemcached||2.3+||Spymemcached caching||Yes, if using Spymemcached|
|xmemcached||1.3+||Xmemcached caching||Yes, if using Xmemcached|
JDO and JPA allow the use of a level 2 (L2) cache, with the cache shared between PersistenceManagers/EntityManagers. The objects in the level 2 cache don't pertain to any one manager. The L2 cache in DataNucleus is as follows :-
The L2 cache stores an object of type org.datanucleus.cache.CachedPC and is keyed by the identity of the object. The CachedPC contains a persistable object (not connected to a StateManager), together with the indicators for which fields are loaded, as well as values for any relation fields. The persistable object will have values as null for any relation fields, and it is these relation field values stored in the CachedPC that provide linkage to other objects.
The relation field values also do not store actual objects; they store the identities of the related objects. For example if an object X has a 1-1 relation with another persistable object Y then in the relation field values for X for that field we store the identity of Y. Similarly if the field is a Collection, then the relation field values will be a Collection of identities of the related objects. This provides isolation of each object in the L2 cache (so objects aren't storing references to other objects and so allowing garbage collection etc).
Objects are stored in the L2 cache in the following situations
Each class can be configured to be cacheable or not. The default for a persistable class is to be cacheable. Configuration is performed via annotations or XML metadata. If a class is not cacheable then objects of that type aren't stored in the L2 cache.
See also :-