This technical presentation by Al Groccia was hard to take seriously when I noticed that the speaker resembled Frank Oz (Miss Piggy, Fozzie Bear, Yoda).

MVS/XA introduced Linklist Lookaside, and it has been enhanced in MVS/ESA and renamed Library Lookaside. Originally, LLA was a kind of DYNABLDL; it built a table of all the directory entries in your link list datasets, and then hooked itself into SVC 18 (BLDL). All link list BLDLs forevermore required no I/O. It was pretty nice.

ESA Library Lookaside has been enhanced to apply to non-linklist datasets and unauthorized libraries. It completely eliminates link list search I/O, and allows more than 16 datasets in your link list. You can add libraries dynamically.

When you change the directory in an LLA library, LLA doesn't automatically find out about it. This means that if you recompile a program, LLA will cause the old version to be fetched until you tell LLA to refresh itself (i.e. re-read the PDS directories). In XA, LLA's refresh function caused it to re-read all the directories in the link list. The ESA version of LLA has a selective refresh ability; you can refresh single libraries, or specific members in those libraries.

Library Lookaside uses VLF, the Virtual Lookaside Facility. VLF is an ESA facility that keeps copies of certain user data in a data space. When you tell VLF to store an object, you give VLF the object's "class" and its "name". Later when you want to retrieve the object, you give VLF its class and name, and VLF retrieves the object from its data space.

Here is how LLA uses VLF: modules that are executed frequently are noted by LLA. LLA loads these programs, pre-relocates them and stores them in a VLF data space. The next time the program is used, instead of using the MVS loader LLA gets VLF to restore the program core-to-core.

In an LLA-equipped system, the order of program search is: Job pack, LLA, FLPA, MLPA, PLPA, LNKLSTxx datasets.