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.
Specifically, LLA improves module fetch performance in the following
ways:
- 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 .