Statistics Rollups Are Evil
It’s pretty common for statistics-gathering software, like MRTG, Cacti, VMware vCenter, etc. to roll statistics up over time by averaging them. This helps save space, as well as cut down on the processing needed to look at & graph the data. The problem is that the process is lossy. These systems save disk, memory, and CPU by averaging the data over longer and longer time periods. Those averages remove spikes and make the data less and less representative of what actually happened on your system or network. It also makes it damn near useless for planning and troubleshooting. Let’s start with an example I drew up in Excel to simulate something like vCenter recording an application server’s CPU load every …