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The architecture of an Ehcache node can include a number of tiers that store data. One of the most important aspects of managing cached data involves managing the life of that data in those tiers.

Use the figure at right with the definitions below to understand the life of data in the tier of Ehcache nodes backed by the Terracotta Server Array, available with BigMemory Max. These definitions apply similarly in standalone Ehcache, but limited to two tiers (heap and disk). BigMemory Go can add an off-heap tier to standalone nodes.

The sections below explore in more detail the aspects of managing data life in Ehcache and the TSA, including the pinning features of Automatic Resource Control (ARC).

Cache entries expire based on parameters with configurable values. When eviction occurs, expired elements are the first to be removed. Having an effective expiration configuration is critical to optimizing use of resources such as heap and maintaining cache performance.

To add expiration, edit the values of the following attributes and tune these values based on results of performance tests:

See How Configuration Affects Element Eviction for more information on how configuration can impact eviction. See this BigMemory Max document on distributed cache configuration for definitions of other available configuration properties.

Data that should remain in the cache regardless of resource constraints can be pinned.

Entire caches can be pinned using the pinning element in cache configuration. This element has a required attribute (store) to specify which data tiers the cache should be pinned to:

The store attribute can have one of the following values:

For example, the following cache is configured to pin its entries:

The following cache is configured to pin its entries to heap only:

Pinning as a setting exists in the local Ehcache client memory. It is never replicated or distributed in a cluster. Pinning achieved programmatically will not be persisted — after a restart the pinned entries are no longer pinned. Cache pinning in configuration is reinstated with the configuration file.

To unpin all of a cache’s pinned entries, clear the cache. Specific entries can be removed from a cache using Cache.remove(). To empty the entire cache, use Cache.removeAll(). If the cache itself is removed (Cache.dispose() or CacheManager.removeCache()), then any data still remaining in the cache is also removed locally.

Caches can also be cleared using the Terracotta Management Console.

The following example shows a cache with certain expiration settings:

Note the following about the myCache configuration:

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