SHMADD

onconfig.std
value

8192

range of values

1024 through 524,288 on 32-bit platforms and 1024 through 4 gigabytes on 64-bit platforms

units

Kilobytes

takes effect

When shared memory is initialized

utilities

onutil

refer to

Virtual portion of shared memory in the shared-memory chapter of the IBM Informix: Administrator's Guide

SHMADD specifies the size of a segment that is dynamically added to the virtual portion of shared memory.

It is more efficient to add memory in large segments, but wasteful if the added memory is not used. Also, the operating system might require you to add memory in a few large segments rather than many small segments.

Use the following guidelines for setting the initial value of SHMADD.

Amount of Physical Memory

Recommended SHMADD Value

Less than 256 megabytes

8192

Greater than 256 megabytes and less than 512 megabytes

16,384

Greater than 512 megabytes

32,768

The following command displays the size of memory segments and the amount of memory that is used or free in each:

onstat -g seg

To modify the SHMADD parameter dynamically, use the onutil SET command. Example:

%onutil
 SHMADD 16384;