Caché Installation Guide - InterSystems Documentation

Calculating System Parameters for OpenVMS
4. If the process's page fault rate drops below PFRATL, OpenVMS removes pages from the
working set in increments of WSDEC until the page fault rate exceeds PFRATL.
5. When the process exits the image, it loses these additional pages. For example, consider
a monthly batch payroll job. When you run it in July, it begins execution at WSDEFAULT,
and gains pages until it reaches WSEXTENT. When you run it in August, it again begins
execution at the default value of WSDEFAULT.
See your OpenVMS documentation for more on the OpenVMS page allocation scheme.
A.3.2 Process Control of Memory Allocation
OpenVMS provides several facilities to alter working set parameters on a process-by-process
or user-by-user basis. The table below summarizes these methods:
Working Set Control
Type of Process
Users
Interactive Processes
Batch Processes
Batch Queues
Method of Working Set Control
The AUTHORIZE utility lets you change the default working set
on a user-by-user basis.
The DCL command SET WORKING_SET allows interactive
processes to change working set parameters.
The SUBMIT command qualifiers for working sets allow batch
processes to alter physical memory allocations.
You can use the DCL command INITIALIZE/QUEUE to alter
working set parameters for batch queues.
A.3.3 Keeping Memory Free for New Processes
Memory is finite. Every time a new process begins under OpenVMS, it takes WSDEFAULT
pages away from the total number of available pages. The remaining memory is available
for the free page list and for WSINC additions to each process's allocation.
Heavily loaded systems can run so many concurrent processes that the number of pages
remaining for use in the free page list becomes very small. OpenVMS includes a parameter
called FREELIM that sets a lower limit for the number of pages in the free page list.
The size of the free and modified page lists directly affects the ratio of hard page faults to
soft page faults. Hard page faults cause a process to experience a resource wait state, resulting
in slow execution. For better performance, it is important to tune the system to minimize hard
56 Caché Installation Guide