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The integrated graphing facility in MageStack uses an excellent utility called Munin (see how to access Munin here). We measure and monitor every facet of the server and every application running, so that we can keep thorough, historical statistics on exactly how your server is running.
Munin is an excellent resource to review near real-time statistics, but it isn't useful for actual real-time statistics. Munin collects the data for the graphs, every 5 minutes, but creating the graphs themselves requires a small amount of CPU to complete, and if run every 5 minutes along with collection, it can cause a noticeable increase in CPU usage. So MageStack uses a facility called
rrdcached to buffer the statistic collection for up to 1 hour, so that the graphs are reproduced every 1 hour, minimising CPU usage by a factor of 12.
So when looking at Munin, the "Current" statistics will usually show
NaN due to the buffering mechanism and the graph itself may be up to 1 hour behind.
If you need real-time statistics, Monit (see how to access Monit here) is the utility to use.