Associating RACF® user IDs and groups to UIDs and GIDs has important performance considerations. It is important to use the Virtual Lookaside Facility (VLF) classes IRRUMAP and IRRGMAP and the UNIXMAP class to improve performance by avoiding sequential searches of the RACF database for UID and GID associations. If your installation shares the RACF database with only systems running z/OS®, you might be able to achieve improved performance without using UNIXMAP. However, before you can avoid using UNIXMAP, you must ask your system programmer if your installation has reached stage 3 of application identity mapping by running the IRRIRA00 conversion utility. If your installation is new to RACF, you will automatically take advantage of application identity mapping at the stage 3 level without running the IRRIRA00 conversion utility, and you will not need to use UNIXMAP to achieve improved performance.