Caché Installation Guide - InterSystems Documentation

By default, Caché automatically allocates shared memory, including routine buffers and global buffers,
to a total of one-eighth of the system available shared memory space. If you plan to run large applications
or support large numbers of users, tune the system according to the following formula:
(number of routine buffers)*32 KB
+ (number of global buffers)*8 KB
+ 4MB
___________________________________
= Shared memory needed
Determine Memory and Disk Requirements
For applications where load growth is reflected in the number of simultaneous direct Caché sessions,
the memory demand to accommodate the processes increases as the computing power increases. For
example, a system that is upgraded from 4 to 8 cores would be capable of supporting a much larger
number of sessions (that is, processes). Since each process consumes memory, it might be necessary
to increase physical memory.
Note:
The amount of memory per process may vary depending on the application and can be larger
than the default value recommended in the UNIX Memory Requirements table.
For configurations dedicated to servers with a limited number of processes (for example, ECP Data
Server or Ensemble), an increase in the load does not necessarily involve a greater number of processes.
Therefore, a larger load on a more powerful system may not require more memory for processes.
B.1.1.1 Support for Huge Memory Pages for Linux
Using pages of much larger size than default saves memory by saving space for PTE tables on the
systems where these tables are not shared by processes and get allocated for each process.
To allocate Huge Pages on Linux, do the following:
1. Check the status
/proc/meminfo contains huge pages information. By default, no huge pages are allocated. Default
huge page size is 2MB. For example:
[root@woodcrest grub]# tail -4 /proc/meminfo
HugePages_Total: 0
HugePages_Free: 0
HugePages_Rsvd: 0
Hugepagesize: 2048 KB
2. Change the number of huge pages.
You can change the system parameter directly: For example, to allocate 2056 Huge Pages, execute:
# echo 2056 > /proc/sys/vm/nr_hugepages
Note:
Alternatively, you can use sysctl(8) to change it:
# sysctl -w vm.nr_hugepages=2056
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