Each time you read a data item from the cache structure or write a data item to the cache structure, you must assign the data item to a storage class. Storage classes allow you to control reclaim processing. By grouping data items with similar attributes into a storage class, you can control from which group (that is, storage class) the system will reclaim resources.

For each storage class, the system maintains a queue of entries that identifies the data items for that storage class. Entries on the queue are kept in a least recently used (LRU) order. When the system needs to reclaim from a particular storage class, the system reclaims resources that are used least recently.

You need to develop algorithms to determine the number of storage classes and the data items to assign to each storage class. You might define only one storage class that meets your needs, or you might define multiple storage classes and base the assignment of data items to different storage classes based on the importance of the data items to your application. For instance, storage class one might identify data entries for data to which the application does not need fast access. Storage class two might identify data entries for data that your application must be able to access quickly. Whenever you read or write the data item, you can also change the data item's storage class.

IXLCACHE REQUEST=READ_STGSTATS returns statistics for a specified storage class. These statistics provide information about the use of cache structure storage.