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Subject: Re: Index interval tuning
From: aaron morton <aaron@thelastpickle.com>
In-Reply-To: <4DC9BE51.7080201@gmail.com>
Date: Wed, 11 May 2011 14:24:05 +1200
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To: user@cassandra.apache.org

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.=20

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.
>>=20
>> 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?
>>=20
>=20
> (=46rom 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.
>=20
> The code looked reasonable until I got to SSTableReader, which was too
> complicated to just glance through.