Chapter 3. Cache Manager
The CacheManager interface is the main entry point to Data Grid and lets you:
- configure and obtain caches
- manage and monitor your nodes
- execute code across a cluster
- more…
Depending on whether you embed Data Grid in applications or run it as a remote server, you use either an EmbeddedCacheManager or a RemoteCacheManager. While they share some methods and properties, be aware that there are semantic differences between them. The following chapters focus mostly on the embedded implementation.
CacheManagers are heavyweight objects, and we foresee no more than one CacheManager being used per JVM (unless specific setups require more than one; but either way, this would be a minimal and finite number of instances).
The simplest way to create a CacheManager is:
EmbeddedCacheManager manager = new DefaultCacheManager();
which starts the most basic, local mode, non-clustered cache manager with no caches. CacheManagers have a lifecycle and the default constructors also call Lifecycle.start(). Overloaded versions of the constructors are available, that do not start the CacheManager, although keep in mind that CacheManagers need to be started before they can be used to create Cache instances.
Once constructed, CacheManagers should be made available to any component that require to interact with it via some form of application-wide scope such as JNDI, a ServletContext or via some other mechanism such as an IoC container.
When you are done with a CacheManager, you must stop it so that it can release its resources: manager.stop();
This will ensure all caches within its scope are properly stopped, thread pools are shutdown. If the CacheManager was clustered it will also leave the cluster gracefully.
3.1. Obtaining caches
After you configure the CacheManager, you can obtain and control caches.
Invoke the getCache(String) method to obtain caches, as follows:
Cache<String, String> myCache = manager.getCache("myCache");
The preceding operation creates a cache named myCache, if it does not already exist, and returns it.
Using the getCache() method creates the cache only on the node where you invoke the method. In other words, it performs a local operation that must be invoked on each node across the cluster. Typically, applications deployed across multiple nodes obtain caches during initialization to ensure that caches are symmetric and exist on each node.
Invoke the createCache() method to create caches dynamically across the entire cluster, as follows:
Cache<String, String> myCache = manager.administration().createCache("myCache", "myTemplate");The preceding operation also automatically creates caches on any nodes that subsequently join the cluster.
Caches that you create with the createCache() method are ephemeral by default. If the entire cluster shuts down, the cache is not automatically created again when it restarts.
Use the PERMANENT flag to ensure that caches can survive restarts, as follows:
Cache<String, String> myCache = manager.administration().withFlags(AdminFlag.PERMANENT).createCache("myCache", "myTemplate");For the PERMANENT flag to take effect, you must enable global state and set a configuration storage provider.
For more information about configuration storage providers, see GlobalStateConfigurationBuilder#configurationStorage().
3.2. Clustering Information
The EmbeddedCacheManager has quite a few methods to provide information as to how the cluster is operating. The following methods only really make sense when being used in a clustered environment (that is when a Transport is configured).
3.3. Member Information
When you are using a cluster it is very important to be able to find information about membership in the cluster including who is the owner of the cluster.
The getMembers() method returns all of the nodes in the current cluster.
The getCoordinator() method will tell you which one of the members is the coordinator of the cluster. For most intents you shouldn’t need to care who the coordinator is. You can use isCoordinator() method directly to see if the local node is the coordinator as well.
