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From Héctor Izquierdo Seliva <izquie...@strands.com>
Subject Re: Index interval tuning
Date Wed, 11 May 2011 07:53:59 GMT
El mié, 11-05-2011 a las 14:24 +1200, aaron morton escribió:
> 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

0.7.5, and I am no longer using key cache. I get the bloom filter stats
via jmx. BloomFilterFalsePositiveRatio is always stuck at 1.0.
RecentBloomFilterFalsePositiveRation fluctuates from 0 to 1.0 with no
intermediate values. 

As for the index interval settings, I changed it from 128 to 256 and
memory consumption was just a tad lower but read performance was worse
by a few ms, so not much to gain there.

> -----------------
> 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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