The reclaim vector defines the storage classes from which the system can reclaim resources to satisfy WRITE_DATA or READ_DATA requests with the specified storage class. The reclaim vector also defines how many times the system can reclaim from each storage class (repeat factor).

Figure 1 shows three reclaim vectors, one for storage class 1, one for storage class 2, and one for storage class 3. In the example of the reclaim vector for storage class 1 requests, the first 3 reclaims to satisfy a request for a data item in storage class 1 come from data items in storage class 1.

The system maintains a counter so that each reclaim from a storage class causes the system to subtract 1 from the reclaim value until the value equals 0. Then the system attempts reclaims from the next storage class based on the reclaim value of that vector entry. The next 2 reclaims for storage class 1 requests come from storage class 2, followed by 5 reclaims from storage class 3.

When the system processes the last reclaim from storage class n as specified by the reclaim vector entry, it subtracts 1 from a counter based on the repeat factor. Based on the repeat factor specified, the system refreshes the reclaim values specified for each storage class entry in the vector and starts the reclaim process again from the beginning of the vector until the repeat counter equals 0. When the counter equals 0, the system deactivates the vector and uses the system default to satisfy requests for that storage class.

The same reclaim processing applies to the vectors specified for storage classes 2 and 3.

Figure 1. Three Reclaim Vectors

To provide a reclaim vector or to restore the default reclaim algorithm, issue an IXLCACHE REQUEST=SET_RECLVCTR request. When you provide a vector, you must also indicate how many times the system is to use the vector before resuming use of the default algorithm. The number of times that the system repeats the process indicated by the reclaim vector is called the repeat factor (specified on the REPEAT keyword). In Figure 1, a repeat factor of 2 (REPEAT=2) for the storage class 1 reclaim vector indicates that the system process the vector twice— 3 reclaims from storage class 1, 2 reclaims from storage class 2, 5 reclaims from storage class 5, and repeat the sequence a second time before it uses the default reclaim algorithm.