Factors affecting performance

When you write applications using the techniques of data-in-virtual, the I/O takes place only for the data referenced and saved. If you run an application using conventional access methods, and then run it again using data-in-virtual, you will notice a difference in performance. This difference depends on both the size of the data set and its access pattern (or reference pattern). Size refers to the magnitude of the data sets that the application must process. The access pattern refers to how the application references the data.

Commercial applications sometimes use data access patterns that are not suitable because they are predictable and sequential. If the access pattern of a proposed application is fundamentally sequential or if the data set is small, a conventional VSAM (or other sequential access method) implementation may perform better than a data-in-virtual implementation. However, this does not rule out commercial applications as data-in-virtual candidates. If the performance factors are favorable, any type of application, commercial or scientific, is suitable for a data-in-virtual implementation.

Before you can use the DIV macro to process a linear data set object or a hiperspace object, you must create either the data set or the hiperspace. z/OS MVS Programming: Extended Addressability Guide explains how to create a hiperspace. Creating a linear data set explains how to create a linear data set.