Fast Path Virtual Storage Option

The Fast Path Virtual Storage Option (VSO) allows you to map data into virtual storage or a coupling facility structure.

You can map one or more DEDB areas into virtual storage or a coupling facility structure by defining the DEDB areas as VSO areas.

For high-end performance applications with DEDBs, defining your DEDB areas as VSO allows you to realize the following performance improvements:

• Reduced read I/O

  After an IMS and VSAM control interval (CI) has been brought into virtual storage, all subsequent I/O read requests read the data from virtual storage rather than from DASD.

• Decreased locking contention
  For VSO DEDBs, locks are released after both of the following:

  • Logging is complete for the second phase of an application synchronization (commit) point
  • The data has been moved into virtual storage

  For non-VSO DEDBs, locks are held at the VSAM CI-level and are released only after the updated data has been written to DASD.

• Fewer writes to the area data set

  Updated data buffers are not immediately written to DASD; instead they are kept in the data space and written to DASD at system checkpoint or when a threshold is reached.

In all other respects, VSO DEDBs are the same as non-VSO DEDBs. Therefore, VSO DEDB areas are available for IMS DBCTL and LU 6.2 applications, as well as other IMS DB or IMS TM applications. Use the DBRC commands INIT.DBDS and CHANGE.DBDS to define VSO DEDB areas.

The virtual storage for VSO DEDB areas is housed differently depending on the share level assigned to the area. VSO DEDB areas with share levels of 0 and 1 are loaded into a z/OS® data space. VSO DEDB areas with share levels of 2 and 3 are loaded into a coupling facility cache structure.

Coupling facility cache structures are defined by the system administrator and can accommodate either a single DEDB area or multiple DEDB areas. Cache structures that support multiple DEDB areas are called multi-area structures. For more information on multi-area structures, see IMS Version 15.5 System Administration.

Recommendation: Terminal-related MSDBs and non-terminal-related MSDBs with terminal-related keys are not supported. Non-terminal-related MSDBs without terminal-related keys are still supported. Therefore, you should consider converting all your existing MSDBs to VSO DEDBs or non-VSO DEDBs.