20.2. Write-Behind Caching

Procedure 20.2. The write-behind Element

<file-store passivation="false" 
            path="${PATH}" 
            purge="true" 
            shared="false">
    <write-behind modification-queue-size="1024" 
                  shutdown-timeout="25000"  
                  flush-lock-timeout="15000" 
                  thread-pool-size="5" />
</file-store>

<file-store passivation="false" 
            path="${PATH}" 
            purge="true" 
            shared="false">
    <write-behind modification-queue-size="1024" 
                  shutdown-timeout="25000"  
                  flush-lock-timeout="15000" 
                  thread-pool-size="5" />
</file-store>

1. The modification-queue-size parameter sets the modification queue size for the asynchronous store. If updates occur faster than the cache store can process the queue, the asynchronous store behaves like a synchronous store. The store behavior remains synchronous and blocks elements until the queue is able to accept them, after which the store behavior becomes asynchronous again.
2. The shutdown-timeout parameter specifies the time in milliseconds after which the cache store is shut down. When the store is stopped some modifications may still need to be applied. Setting a large timeout value will reduce the chance of data loss. The default value for this parameter is 25000.
3. The flush-lock-timeout parameter specifies the time (in milliseconds) to acquire the lock that guards the state to be periodically flushed. The default value for this parameter is 15000.
4. The thread-pool-size parameter specifies the size of the thread pool. The threads in this thread pool apply modifications to the cache store. The default value for this parameter is 5.

Procedure 20.3. The async Element

<persistence>
    <singleFile location="${LOCATION}">
        <async enabled="true" 
                    modificationQueueSize="1024" 
                    shutdownTimeout="25000" 
                    flushLockTimeout="15000" 
                    threadPoolSize="5"/>
    </singleFile>
</persistence>

<persistence>
    <singleFile location="${LOCATION}">
        <async enabled="true" 
                    modificationQueueSize="1024" 
                    shutdownTimeout="25000" 
                    flushLockTimeout="15000" 
                    threadPoolSize="5"/>
    </singleFile>
</persistence>

1. The modificationQueueSize parameter sets the modification queue size for the asynchronous store. If updates occur faster than the cache store can process the queue, the asynchronous store behaves like a synchronous store. The store behavior remains synchronous and blocks elements until the queue is able to accept them, after which the store behavior becomes asynchronous again.
2. The shutdownTimeout parameter specifies the time in milliseconds after which the cache store is shut down. This provides time for the asynchronous writer to flush data to the store when a cache is shut down. The default value for this parameter is 25000.
3. The flushLockTimeout parameter specifies the time (in milliseconds) to acquire the lock that guards the state to be periodically flushed. The default value for this parameter is 15000.
4. The threadPoolSize parameter specifies the number of threads that concurrently apply modifications to the store. The default value for this parameter is 5.