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From aaron morton <aa...@thelastpickle.com>
Subject Re: Index interval tuning
Date Wed, 11 May 2011 02:24:05 GMT
What version and what were the values for RecentBloomFilterFalsePositives and BloomFilterFalsePositives
?

The bloom filter metrics are updated in SSTableReader.getPosition() the only slightly odd
thing I can see is that we do not count a key cache hit a a true positive for the bloom filter.
If there were a lot of key cache hits and a few false positives the ratio would be wrong.
I'll ask around, does not seem to apply to Hectors case though. 

Cheers

-----------------
Aaron Morton
Freelance Cassandra Developer
@aaronmorton
http://www.thelastpickle.com

On 11 May 2011, at 10:38, Chris Burroughs wrote:

> On 05/10/2011 02:12 PM, Peter Schuller wrote:
>>> That reminds me, my false positive ration is stuck at 1.0, so I guess
>>> bloom filters aren't doing a lot for me.
>> 
>> That sounds unlikely unless you're hitting some edge case like reading
>> a particular row that happened to be a collision, and only that row.
>> This is from JMX stats on the column family store?
>> 
> 
> (From jmx)  I also see BloomFilterFalseRatio stuck at 1.0 on my
> production nodes.  The only values that RecentBloomFilterFalseRatio had
> over the past several minutes were 0.0 and 1.0.  While I can't prove
> that isn't accurate, it is very suspicions.
> 
> The code looked reasonable until I got to SSTableReader, which was too
> complicated to just glance through.


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