Output processing

During phase 1 of synchronization point processing, VSO data is treated the same as non-VSO data. The use of VSO is transparent to logging.

During phase 2 of the synchronization point processing, VSO and non-VSO data are treated differently. For VSO data, the updated data is copied to the data space, the lock is released and the buffer is returned to the available queue. The relative byte address (RBA) of the updated CI is maintained in a bitmap. If the RBA is already in the bitmap from a previous update, only one copy of the RBA is kept. At interval timer, the updated CIs are written to DASD. This batching of updates reduces the amount of output processing for CIs that are frequently updated. While the updates are being written to DASD, they are still available for application programs to read or update because copies of the data are made within the data space just before it is written.

For SHARELVL(2|3) VSO areas, the output thread process is used to write updated CIs to the coupling facility structures. When the write is complete, the lock is released. XES maintains the updated status of the data in the directory entry for the CI.