The virtual lookaside facility (VLF)

Virtual lookaside facility (VLF) is a set of services that can improve the performance and response time of applications that must retrieve a set of data for many users. VLF creates and manages a data space to store an application's most frequently used data. When the application makes a request for data, VLF checks its data space to see if the data is there. If the data is present, VLF can rapidly retrieve it without requesting I/O to DASD.

To take advantage of VLF, an application must identify the data it needs to perform its task. The data is known as a data object. Data objects should be small to moderate in size, named according to the VLF naming convention discussed later in this information, and associated with an installation-defined class of data objects.

VLF is intended for use with major applications. Because VLF runs as a started task that the operator can stop or cancel, it cannot take the place of any existing means of accessing data on DASD. Any application that uses VLF must also be able to run without it.

An installation can realize immediate benefits from VLF by using some of the products that use VLF. See z/OS MVS Initialization and Tuning Guide for information about how to achieve these benefits.