Why and when to perform this task
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:
Steps for this task
Results
Application servers must have different disk offload locationsWhen you have two or more application servers with servlet caching enabled and the application servers 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 non-root, this problem could occur. For example, if server1 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 non-root servers to crash when they try to read or write to the cache.
The disk offload function is restricted to a single server region on z/OS.