Introduction

Users with large Nagios Core installations may benefit from the use_large_installation_tweaks configuration option. Enabling this option allows the Nagios Core daemon to take certain shortcuts which result in lower system load and better performance.

Effects

When you enable the use_large_installation_tweaks option in your main Nagios Core config file, several changes are made to the way the Nagios Core daemon operates:

1. No Summary Macros In Environment Variables
   The summary macros will not be available to you as environment variables. Calculating the values of these macros can be quite time-intensive in large configurations, so they are not available as environment variables when use this option. Summary macros will still be available as regular macros if you pass them to to your scripts as arguments.
2. No Group Member Macros In Environment Variables
   The $HOSTGROUPMEMBERS$ and $SERVICEGROUPMEMBERS$ macros will not be available to you as environment variables. The values of these macros can be quite large and could possibly consume of all the environment variable space in large configurations, so they are not available as environment variables when use this option. These macros will still be available as regular macros if you pass them to to your scripts as arguments.
3. Different Memory Cleanup
   Normally Nagios Core will free all allocated memory in child processes before they exit. This is probably best practice, but is likely unnecessary in most installations, as most OSes will take care of freeing allocated memory when processes exit. The OS tends to free allocated memory faster than can be done within Nagios Core itself, so Nagios Core won't attempt to free memory in child processes if you enable this option.