On each READ_DATA request, you specify whether you want the system to define the data item to the structure. If you do not know whether the data item is currently assigned a directory entry in the cache structure, specify ASSIGN=YES (which is also the system default). If a directory entry for the data item does not exist in the cache structure, this request defines the directory entry to the cache structure. Directory-only cache systems use this option to allocate only the directory entry for a data item in the structure.

If you specify ASSIGN=YES and cache structure resources are available, the system allocates a directory entry for the named data item. If resources are unavailable for the directory entry, and currently allocated resources cannot be reclaimed, the system fails the request. If the data item already has a directory entry allocated, the request does not define a second directory entry, and the system registers the user's interest in the data item. If the data item has a directory and a data entry associated with it, the request reads the data to your local cache buffer and the system re-registers user interest in the data item.

If you do not want the system to define the data item to the structure, code ASSIGN=NO. Store-in and store-through cache users use this option to read a currently cached data item.

If the data is available, ASSIGN=NO causes the system to transfer the requested data to your storage. If the named data item is currently undefined and you code ASSIGN=NO, the system fails the request.

The system registers interest in the data item if the READ_DATA request allocates a directory entry or re-registers interest in the data item if the directory entry is already allocated.

For general information on specifying the vector index entry, see Specifying the Vector Entry Index on IXLCACHE Requests.