The previous results indicate that you will likely not see any performance degradation from using ModSecurity unless Apache starts consuming too much memory, or you are using a large number of rules and a slow system. What can you do if you do run into either the memory or processor becoming overloaded? This part of the chapter gives some practical advice to help you squeeze the best performance out of your ModSecurity setup.
Adding extra RAM to your server may not be the first or easiest thing to do when you find that the web server processes use too much memory, and therefore it pays to know how to decrease the memory footprint of each Apache process.
Follow these tips and you may not have to add any extra memory:
Decrease Apache module usage
The number of dynamic modules that Apache has to load has a direct impact on the memory footprint of each process. Therefore, tweak your
httpd.conffile so that any modules which you don't require are disabled...
