What are the implications of using SingletonEhCacheRegionFactory vs. EhCacheRegionFactory for Hibernate 2nd-level cache in a Web Application?

Question

While integrating two subsystems, we were forced to use multiple SessionFactory instances, which lead to trouble when interacting with our Hibernate second-level cache (Terracotta EhCache). Specifically:

 for(CacheManager cm : CacheManager.ALL_CACHE_MANAGERS){
            LOGGER.log(Level.DEBUG, "In cm " + cm.getName());
            for(String cn : cm.getCacheNames()){
                LOGGER.log(Level.DEBUG, "I have a cache called " + cn);
                LOGGER.log(Level.DEBUG, "it's status is " + ms.getCache(cn).getStatus());
            }
        }
  try{
     myCollection.size();
  }catch(IllegalStateException ise){
      LOGGER.log(Level.FATAL, ise);  //Triggered
  }        

The debug print-out shows STATUS_ALIVE for cache "Foo" but the call to size() throws an IllegalStateException:

java.lang.IllegalStateException: The Foo Cache is not alive.

Currently, both SessionFactories are configured to use SingletonEhCacheRegionFactory. If I switch the SessionFactories to use EhCacheRegionFactory (non-singleton), what are the ramifications for cache behavior (specifically in a Web App context)?

Answer 1

EhCache will ensure that all instances of SingletonEhCacheRegionFactory use the same actual CacheManager internally, no matter how many instances of SingletonEhCacheRegionFactory you create, making it a crude version of the Singleton design pattern.

The plain EhCacheRegionFactory, on the other hand, will get a new CacheManager every time.

If you have two Hibernate session factories in Spring, each using their own instance of SingletonEhCacheRegionFactory, then they're actually going to end up sharing a lot of their cache state, which may account for your problem.

This isn't really a good match for Spring, where the singletons are supposed to be managed by the container. If you use EhCacheRegionFactory, then you'll likely get more predictable results. I suggest giving it a go and see how you get on.