Configure the dynamic cache disk offload

By default, when the number of cache entries reaches the configured limit for a given WebSphere server, eviction of cache entries occurs, allowing new entries to enter the cache service. The dynamic cache includes an alternative feature named disk offload, that copies the evicted cache entries to disk for potential future access.

To configure disk offload...

1. Open the administrative server.

2. Click Server > Application Server in the administrative console navigation tree.

3. Click server.

4. Click Dynamic Cache Service.

5. Click the Enable disk offload check box in the Disk offload field. You can also set the disk offload location in this field.

6. Click Apply or OK.

Application servers must have different disk offload locations

When you have two or more appservers with servlet caching enabled and the appservers specify the same disk offload location for their caches through the dynamic cache service, the following exceptions might occur

java.lang.NullPointerException
       at com.ibm.ws.cache.CacheOnDisk.readTemplate(CacheOnDisk.java:686)
       at com.ibm.ws.cache.Cache.internalInvalidateByTemplate(Cache.java:828)

or

java.lang.NullPointerException
       at com.ibm.ws.cache.CacheOnDisk.readCacheEntry(CacheOnDisk.java:600)
       at com.ibm.ws.cache.Cache.getCacheEntry(Cache.java:341)

If one server is run as root and the other servers are run as nonroot, this problem could occur. For example, if server runs as root and server2 runs as wasuser or wasgroup, the cache files in the disk offload location might be created with root permissions. This situation causes the applications running on the nonroot servers to crash when they try to read or write to the cache.

The disk offload location must be unique for servers defined on the same node. If you have multiple servers defined on the same node, make sure the disk offload location is different for each server as defined on the Dynamic Cache Service panel, Offload location field.

 

See Also

Enabling the dynamic cache service
Configuring Edge Side Include caching
Dynamic cache service settings

 

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