19.4. Single File Cache Store

Red Hat JBoss Data Grid includes one file system based cache store: the SingleFileCacheStore.
The SingleFileCacheStore is a simple file system based implementation and a replacement to the older file system based cache store: the FileCacheStore.
SingleFileCacheStore stores all key/value pairs and their corresponding metadata information in a single file. To speed up data location, it also keeps all keys and the positions of their values and metadata in memory. Hence, using the single file cache store slightly increases the memory required, depending on the key size and the amount of keys stored. Hence SingleFileCacheStore is not recommended for use cases where the keys are too big.
To reduce memory consumption, the size of the cache store can be set to a fixed number of entries to store in the file; however, this works only when JBoss Data Grid is used as a cache. When JBoss Data Grid is used this way, data which is not present in the cache can be recomputed or re-retrieved from the authoritative data store and stored in the JBoss Data Grid cache. This limitation exists so that once the maximum number of entries is reached older data in the cache store is removed. If JBoss Data Grid were used as an authoritative data store in this scenario it would lead to potential data loss.
Due to its limitations, SingleFileCacheStore can be used in a limited capacity in production environments. It can not be used on shared file system (such as NFS and Windows shares) due to a lack of proper file locking, resulting in data corruption. Furthermore, file systems are not inherently transactional, resulting in file writing failures during the commit phase if the cache is used in a transactional context.
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19.4.1. Single File Store Configuration (Remote Client-Server Mode)

The following is an example of a Single File Store configuration for Red Hat JBoss Data Grid's Remote Client-Server mode: 
<local-cache name="default" statistics="true">
    <file-store name="myFileStore"
                passivation="true"
                purge="true"
                relative-to="{PATH}"
                path="{DIRECTORY}"
                max-entries="10000"
                fetch-state="true"
                preload="false" />
</local-cache>
For details about the elements and parameters used in this sample configuration, see Section 19.3, “Cache Store Configuration Details (Remote Client-Server Mode)”.
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19.4.2. Single File Store Configuration (Library Mode)

In Red Hat JBoss Grid's Library mode, configure a Single File Cache Store as follows:. 
<local-cache name="writeThroughToFile">
      <persistence passivation="false">
         <file-store fetch-state="true" 
                      purge="false" 
                      shared="false"
                      preload="false"
                      location="/tmp/Another-FileCacheStore-Location"
                      max-entries="100">
            <write-behind enabled="true" 
    	           threadPoolSize="500"
    	           flush-lock-timeout="1"
	           modification-queue-size="1024"
	           shutdown-timeout="25000"/>
        </singleFile>
      </persistence>
 </local-cache>
For details about the elements and parameters used in this sample configuration, see Section 19.2, “Cache Store Configuration Details (Library Mode)”.
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19.4.3. Upgrade JBoss Data Grid Cache Stores

Red Hat JBoss Data Grid 7 stores data in a different format than previous versions of JBoss Data Grid. As a result, the newer version of JBoss Data Grid cannot read data stored by older versions. Use rolling upgrades to upgrade persisted data from the format used by the old JBoss Data Grid to the new format. Additionally, the newer version of JBoss Data Grid also stores persistence configuration information in a different location.
Rolling upgrades is the process by which a JBoss Data Grid installation is upgraded without a service shutdown. For JBoss Data Grid servers, this procedure refers to the server side components. The upgrade can be due to either hardware or software change, such as upgrading JBoss Data Grid.
Rolling upgrades are only available in JBoss Data Grid's Remote Client-Server mode.
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