Caché Installation Guide - InterSystems Documentation

OpenVMS Physical Memory Allocation
A.3.1 Default Memory Allocation
The following steps summarize the algorithm OpenVMS uses to determine the amount of physical
memory available to each process. Each capitalized term represents a system parameter that OpenVMS
uses in allocating physical memory.
1. The process begins executing an image. OpenVMS allocates to it the number of pagelets specified
by the quota parameter WSDEFAULT.
Page Allocation:
0--->WSDEFAULT
2. If the process has a higher page fault rate than PFRATH, OpenVMS allocates more pagelets to it.
OpenVMS allocates these pagelets in increments of WSINC until the process has WSQUOTA total
pagelets.
Page Allocation:
0--->WSDEFAULT-->WSINC-->WSINC-->WSQUOTA
3. If the process continues to have a high page fault rate and the free list size exceeds BORROWLIM,
OpenVMS will continue to allocate pagelets in WSINC blocks until the free list size is inadequate
or WSEXTENT is reached.
Page Allocation:
0-->WSDEFAULT-->WSINC-->WSQUOTA-->WSINC-->WSEXTENT
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 userby-user
basis. The following table summarizes these methods:
Caché Installation Guide 71