On Tue, Nov 2, 2010 at 1:28 AM, Daniel Doubleday <daniel.double...@gmx.net> wrote: > Hi all > > had some time yesterday to dig a lil deeper. And maybe this saves someone who > made the same mistake the time so ... > > After trying to reproduce the problem in unit tests with the same data which > led nowhere because every single result was almost exactly what the math > promised and incidentally stumbling upon this one: > http://sites.google.com/site/murmurhash/murmurhash2flaw thinking omg all is > lost ... I finally found that everything is just fine. > > Turns out that the jmx BloomFilterFalseRation simply does not show what I > expected it to be. I thought it would provide a quality measure how good the > bloom filter works in terms of hit rate. Which would be (Unnecessary File > Lookups / Total Lookups) but it is ( False Positives / ( False + True > Positives) ) which means it does not count all hits that where rejected by > the filter. > > So if you would only ask for rows that do not exist this ration will always > show 1.0 > > Meaning it is rather a measure of how many of your queries ask for non > existing values.
That sounds like something we should change. -ryan
