... properly that is :)
I'm monitoring some very busy NFS clients and would like to graph the
segmap cache hits and misses. I took a look inside the code of the
segmapstat script included in Mr. Gregg's CacheKit collection, and I'm
getting some negative misses values in the results.
The hits and misses are being calculated in segmapstat as such:
hits = get_reclaim + get_use
misses = getmap - hits
The get_reclaim, get_use, and getmap are kstats (see 'kstat -m unix -n
segmap')
The problem I have on some servers is that the value for misses is
negative because the value for hits is far larger than the value of
getmap. Is this really a valid scenario?
Going on the above equation with data from an example server:
get_reclaim = 4259681823
get_use = 11302007
getmap = 842307023
So:
hits = 4259681823 + 11302007 = 4270983830
misses = 842307023 - 4270983830 = -3428676807
This doesn't seem right. Well, it *isn't* right. I don't know how one
could have negative anything in the context of counting cache hits and
misses. Any thoughts? Are there other kstats I should be looking at to
derive these values?
/dale
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