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Monday, April 25, 2011

UCL=LCL : How many standard deviations do we use for Control Charting? Use ZERO!

How many standard deviations do we use for upper (UCL) and lower (LCL) limits calculations on a control charts? 3? 1? What about 0 st. dev.!? Indeed, the simplest way to build MASF data for exception detection is to use 168 weekly hours averages as a baseline, so that would be the case when ZERO st. Dev is used to make UCL=LCL! Plus for further simplification the current data could be included in wider historical baseline (Why not?). My EV meta-metric in this case would be just difference between actual metric value and the average over baseline!

Here is example of DB2-like SQL script to implement that approach. It is based on real script I developed and successfully tested against real data for BIRT tool to get exceptional servers list:
 

(In this SQL script example metrics names as well as some other fields parsing (e.g. week day and hour) are dropped to increase readability; for real usage that script needs to be adjusted to the real PDB type, metrics names and schema.)


So the SEDS-lite project could be implemented using BIRT reporting (no real programming needed – just SQL scripting and report design!) and the script above could be a good example of ETL step on the SEDS-lite architecture for building SEDS DB out of raw data (see my other post linked here) for charting and exception detecting



"Все гениальное - просто" = KEEP IT SIMPLE!