Virtual Lookaside Facility (VLF)

  • VLF keeps objects (for example Load modules) in Virtual Storage in order to save I/O operations that would load such objects.
  • Designed primarily to improve performance by retrieving the most currently used objects from Virtual Storage rather then performing repetitive I/O operations from DASD.
  • VLF can be configured by using PARMLIB member COFVLFxx.

Examples of some VLF exploiters:

  • LLA (for Load modules)
  • TSO (for REXX and CLIST procedures)
  • CAS – Catalog Address Spaces (for User Catalog entries)
  • RACF records from its database

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