Healing pointers
The self-healing process updates or corrects the information in extended pointer sets.
When the ILE is used, the information about the current location of the segment in the ILE is moved to the EPS. This allows IMS to avoid the indirect process if the EPS is used for a later retrieval. This correction to the EPS in the database buffer pool is always done.
Because of locking considerations, the update might not be written to the database on DASD. The buffer containing the entry or segment with the updated EPS is marked as altered if the application program is allowed to update the database. The call must be done with a PCB allowing updates, and the IMS system must have an access intent for the partition that allows updates. If updates are not allowed, the buffer is not marked as altered.
When the application reaches a sync point, it does not write buffers to DASD if they are not marked as altered. If the updated EPS is not written to DASD, the next time it is retrieved from DASD and used to find its target, IMS must use the indirect process. That is, IMS must read the ILE again.
The following figure shows the EPS after it has been healed. The RBA points to the current location. The partition ID is correct. The partition reorganization number matches the number stored in the partition database data set.
