Caché Installation Guide - InterSystems Documentation

Calculating System Parameters for OpenVMS
can be loaded into the empty buffer as it is required by another Caché process. If all buffers
are occupied when Caché needs to load a routine, it chooses the least recently used (LRU)
buffer, not the least frequently used (LFU) buffer. Allowing more buffers enhances performance.
The nature of the application influences the appropriate number of buffers. If many users
access a small number of routines, a relatively small number of buffers will suffice for optimum
response time. Conversely, an application with a large number of routines will benefit from
a large number of buffers.
The parameter calculator starts with a default value for the number of routine buffers. This
default is based upon a medium-sized site. You can enter a different value for this parameter
in the Routine Buffer Pool field in the parameter calculator based on the specifics of your site.
Note:
If you prefer to enter a value in this field with an MB unit of measure, this value is
used for the Memory for Routine Cache (MB) field in the Calculation Result section
and also in calculations involving routine buffers; it is not recalculated.
A.5.1.3 Determine Number of Global Buffers Per Process
The parameter calculator assumes the global buffers are 8 KB in size. The calculator starts
with recommended “rule of thumb” values for clustered and nonclustered systems.
If your system is memory-poor, you can reduce this value. Do not, however, decrease it below
a multiple of 32 KB per process.
Using more global buffers helps the performance of most sites. You can use the statistics
produced by the ^GLOSTAT utility to determine if adding more global buffers will reduce
disk access and thereby improve performance.
A.5.2 Record Current OpenVMS Parameter Values
Every system has memory needs other than those for Caché. For example, there are memory
requirements for FORTRAN and COBOL layered products as well as for OpenVMS itself.
To analyze these requirements for your system, follow the procedures below to display the
values of the indicated parameters prior to installing Caché.
Note:
If you are performing an upgrade, shut down Caché to get accurate numbers.
1. Run the OpenVMS SYSGEN utility to display the current value of each parameter listed
in the OpenVMS System Parameter Values Table.
60 Caché Installation Guide