Partition selection when processing is restricted to a single partition

If you use high key partitioning, IMS selects partitions by using the root key that is used in the DL/I call and the high key that is defined for the partition. When access is restricted to a single partition and the root key is outside of the key range of the partition, IMS returns an FM or GE status code.

If you use a partition selection exit routine to select partitions, the routine is called when the DL/I call provides a specific root key. The exit routine selects a partition based on the specified root key. If the partition that is selected is different from the one that the application has access to, IMS returns an FM or GE status code.

When access is restricted to a single partition, the first partition is always the partition to which access is restricted, and the next partition does not exist. The exit routine is not called to select a first partition or the next partition.

Recommendation: When restricting processing to a single partition, include in the SSA only the root keys that are in the key range of the partition.