Improving module fetch performance with LLA
You can improve the performance of module fetching on your system by allowing library lookaside (LLA) to manage your production load libraries. LLA reduces the amount of I/O needed to locate and fetch modules from DASD storage.
- By maintaining (in the LLA address space) copies of the library directories the system uses to locate load modules. The system can quickly search the LLA copy of a directory in virtual storage instead of using costly I/O to search the directories on DASD.
- By placing (or staging) copies of selected modules in a virtual lookaside facility (VLF) data
space (when you define the LLA class to VLF, and start VLF). The system can quickly fetch modules
from virtual storage, rather than using slower I/O to fetch the modules from DASD.
LLA determines which modules, if staged, would provide the most benefit to module fetch performance. LLA evaluates modules as candidates for staging based on statistics it collects about the members of the libraries it manages (such as module size, frequency of fetches per module (fetch count), and the time required to fetch a particular module).
If necessary, you can directly influence LLA staging decisions through installation exit routines (CSVLLIX1 and CSVLLIX2). For information about coding these exit routines, see z/OS MVS Installation Exits.