Chapter 4. Cache Loaders

A cache loader is the connection of JBoss Cache to a (persistent) data store. The cache loader is called by JBoss Cache to fetch data from a store when that data is not in the cache, and when modifications are made to data in the cache the Cache Loader is called to store those modifications back to the store.

In conjunction with eviction policies, JBoss Cache with a cache loader allows a user to maintain a bounded cache for a large backend datastore. Frequently used data is fetched from the datastore into the cache, and the least used data is evicted, in order to provide fast access to frequently accessed data. This is all configured through XML, and the programmer doesn't have to take care of loading and eviction.

JBoss Cache currently ships with several cache loader implementations, including:

No, it is not. The FileCacheLoader has some severe limitations which restrict its use in a production environment, or if used in such an environment, it should be used with due care and sufficient understanding of these limitations.

As a rule of thumb, it is recommended that the FileCacheLoader not be used in a highly concurrent, transactional or stressful environment, and its use is restricted to testing.

Yes. Set the async attribute to true. See the JBoss Cache Users' Guide for a more detailed discussion. By default though, all cache loader writes are synchronous and will block.

Yes. A cache loader is a class implementing org.jboss.cache.loader.CacheLoader or extending org.jboss.cache.loader.AbstractCacheLoader. It is configured via the XML file (see JBoss Cache User Guide).

No. A cache loader could, for example, fetch (and possibly store) its data from a webdav-capable webserver. Another example is a caching proxy server, which fetches contents from the web. Note that an implementation of CacheLoader may not implement the 'store' functionality in this case, but just the 'load' functionality.

Yes. Within the CacheLoaderConfiguration XML element (see the JBoss Cache User Guide chapter on cache loaders) you can describe several cache loaders. The impact is that the cache will look at all of the cache loaders in the order they've been configured, until it finds a valid, non-null element of data. When performing writes, all cache loaders are written to (except if the ignoreModifications element has been set to true for a specific cache loader).

Yes. See the "Transforming Cache Loaders" section within the "Cache Loaders" section located in the JBoss Cache User Guide.

As of JBoss Cache 2.1.0, the answer is yes. See the JBoss Cache User Guide for details on how to configure and tune your retries and wait period for reestablishing the TCP connection.

Prior to that, restarting the TCPCacheServer would also mean restarting your application that uses the cache.