Chapter 21. Cache Writing Modes

Red Hat JBoss Data Grid presents configuration options with a single or multiple cache stores. This allows it to store data in a persistent location, for example a shared JDBC database or a local file system. JBoss Data Grid supports two caching modes:
  • Write-Through (Synchronous)
  • Write-Behind (Asynchronous)
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21.1. Write-Through Caching

The Write-Through (or Synchronous) mode in Red Hat JBoss Data Grid ensures that when clients update a cache entry (usually via a Cache.put() invocation), the call does not return until JBoss Data Grid has located and updated the underlying cache store. This feature allows updates to the cache store to be concluded within the client thread boundaries.
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21.1.1. Write-Through Caching Benefits and Disadvantages

Write-Through Caching Benefits

The primary advantage of the Write-Through mode is that the cache and cache store are updated simultaneously, which ensures that the cache store remains consistent with the cache contents.

Write-Through Caching Disadvantages

Due to the cache store being updated simultaneously with the cache entry, there is a possibility of reduced performance for cache operations that occur concurrently with the cache store accesses and updates.

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21.1.2. Write-Through Caching Configuration (Library Mode)

No specific configuration operations are required to configure a Write-Through or synchronous cache store. All cache stores are Write-Through or synchronous unless explicitly marked as Write-Behind or asynchronous. The following procedure demonstrates a sample configuration file of a Write-Through unshared local file cache store.

Procedure 21.1. Configure a Write-Through Local File Cache Store

<local-cache name="persistentCache">
		<persistence>
		    <file-store fetch-state="true" 
			    purge="false"
			    shared="false"
			    location="${java.io.tmpdir}"/>
		</persistence>
</local-cache>
  1. The name parameter specifies the name of the local-cache to use.
  2. The fetch-state parameter determines whether the persistent state is fetched when joining a cluster. Set this to true if using a replication and invalidation in a clustered environment. Additionally, if multiple cache stores are chained, only one cache store can have this property enabled. If a shared cache store is used, the cache does not allow a persistent state transfer despite this property being set to true. The fetch-state parameter is false by default.
  3. The purge parameter specifies whether the cache is purged when initially started.
  4. The shared parameter is used when multiple cache instances share a cache store and is now defined at the cache store level. This parameter can be set to prevent multiple cache instances writing the same modification multiple times. Valid values for this parameter are true and false.
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