Emergency restart processing

Recovery of VSO areas across IMS or z/OS® failures is similar to recovery of non-VSO areas. IMS examines the log records, from a previous system checkpoint to the end of the log, to determine if there are any committed updates that were not written to DASD before the failure.

If any such committed updates are found, IMS will REDO them (apply the update to the CI and write the updated CI to DASD). Because VSO updates are batched together during normal processing, VSO areas are likely to require more REDO processing than non-VSO areas.

During emergency restart log processing, IMS tracks VSO area updates differently depending on the share level of the VSO area. For share levels 0 and 1, IMS uses data spaces to track VSO area updates. For share levels 2 and 3, IMS uses a buffer in memory to track VSO area updates.

IMS also obtains a single non-DREF data space which it releases at the end of restart. If restart log processing is unable to get the data space or main storage resources it needs to perform VSO REDO processing, the area is stopped and marked as recovery needed.

By default, at the end of emergency restart, IMS opens areas defined with the PREOPEN or PRELOAD options. IMS then loads areas with the PRELOAD option into a data space or coupling facility structure. You can alter this behavior by using the FPOPN keyword of the IMS procedure to have IMS restore all VSO DEDB areas to their open or closed state at the time of the failure.

VSO areas without the PREOPEN or PRELOAD options are assigned to a data space during the first access following emergency restart.

After an emergency restart, the VSO options and PREOPEN|NOPREO options in effect for an area are those that are defined to DBRC, which may not match those in effect at the time of the failure. For example, a non-shared VSO area removed from virtual storage by the /VUNLOAD command before the failure, is restored to the data space after the emergency restart. For shared VSO areas, the area remains unloaded until the next /STA AREA command is issued for it.