Establishing a Cast-Out Process

To ensure that the system can reclaim storage in the cache structure for subsequent requests, you must periodically cast out changed data items. You can develop a protocol by assigning multiple cast-out classes based on frequency. You might set a “fast” timer to trigger cast-out processing for data items belonging to the “frequently updated” storage class, and a “slow” timer to trigger cast-out processing for infrequently updated data items. Or, you could base your cast-out algorithm on how many changed data items there are in a certain cast-out class. When the number of changed data items reaches that limit, you can cast out the data items.

For each specified data item on the IXLCACHE READ_DIRINFO request, the system returns the cast-out class for the data item and an indication whether the data item is changed. Using this and other information can help you make decisions about how to perform cast-out processing. Using the IXLCACHE macro, you can obtain:

Directory information for specified data items (REQUEST=READ_DIRINFO).
Cast-out statistics for specified cast-out classes (REQUEST=READ_COSTATS)
Cast-out information for a specified cast-out class (REQUEST=READ_COCLASS)
Storage statistics for specified storage classes (REQUEST=READ_STGSTATS)

You can use the following information that these requests return to make your cast-out decisions:

The cast-out class for a data item
The changed/unchanged state of the data item
The total number of changed or locked for cast-out data items in a specified storage class
The total number of data elements allocated to the data items in a specified storage class
The total number of data elements allocated to the data items in a specified cast-out class
The names of data items belonging to a cast-out class
The user-data associated with data items belonging to a cast-out class

Based on monitoring cast-out information that the system returns for pre-defined thresholds, you can invoke a process to cast-out selected data items.

For more information about obtaining information that can help you manage a cast-out process, see: