Sorry for misleading you, but my initial example is bogus - I merely tried to illustrate the problem I had in requiring the zero-values to be significant in the ratio.

The real-life alert is called the Thrashing Severity Ratio, and is for a po:fr ratio = 1/6 (17%). This is described by Tom Farwell in a writeup of paging spaces, and may be somewhat specific to IBM's AIX.

My problem with that writeup is two-fold:
1. Periods of inactivity (0,0 values) are not given enough weight (this may lead to false positives)
2. The overall volume (po = 4k pages swapped to paging) is not considered, and low volume spikes may provide additional false positives (but NOT if sustained).

I should perhaps have mentioned the actual problem from the start, but I fear the downvote of Monks who feel that this discussion is not close enough to a pure perl problem!

Niel