Monitoring CPU usage

Before looking at the Informix CPU usage it is important to monitor the processors at a Unix level (sar, vmstat etc). Monitor the %idle over time to will see if the processors is overloaded, a large percentage shown in the %sys column may signal a problem with the application. Increasing the number of Informix CPU virtual processors on a machine that is already struggling will, in most cases, make the situation worse not better.

Within Informix the majority of the work is done within the CPU vps. The onstat -g glo command will display a per vp CPU usage, alternatively the sysvpprof SMI table can be queried.

If the CPU vp usage over a minute is approaching 60 seconds then the vp is very busy and the system might benefit from an additional CPU vp. Again the system might benefit from an additional CPU vp if there is always threads waiting to run. You can monitor the entries in the ready queue by running onstat -g rea. Generally you do not want more CPU vps than you have physical processors but with the latest high speed processors benefits can seen if CPU vps is set to 1.5-2.0 times the number of physical processors

There will come a point where adding more CPU vps will not improve the performance of the system and either more or faster physical processors will be required.