Use this task to configure dynamic cache disk offload, which saves cache entries that are deleted from the memory cache to disk.
By default, when the number of cache entries reaches the configured limit for a given application server, cache entries are removed from the memory cache, allowing newer entries to be stored in the cache. Use disk offload to copy the cache entries that are being removed from the memory cache to disk for potential future access.
You
can use disk offload if you have one servant in your application server. If
there are multiple servants enabled in your configuration, do not enable disk
offload. If you enable disk offload for an application server that has multiple
servants, each servant attempts to save data to the same location on the disk.
For more information about enabling and disabling multiple servants, see Enabling multiple servants on z/OS.
You enabled disk offload. Memory cache entries are moved to disk for potential future access.
When 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.
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