If you have changed data in the cache structure, you need to cast out the data to permanent storage. Because the system does not reclaim changed data items, developing an efficient protocol for casting out data is essential for managing the reclaim of resources for the cache structure.

Each time you write a changed data item to the cache structure, the system marks the data item as changed. A data item that is marked as changed remains that way until you successfully cast-out the data item. When you free the cast-out lock after having cast out the data but are unable to write the data item to permanent storage, you can issue an IXLCACHE request to free the cast-out lock and indicate that the data item remain marked as changed. As long as the data item is marked as changed or locked for cast out processing, the system does not reclaim resources for the data item.

When a high percentage of data items are marked as changed, the amount of storage available for reclaim is limited. If the amount of free storage available for new data items is limited, you might be unable to define new data items to the cache structure.