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From Radim Kolar <>
Subject Re: reported bloom filter FP ratio
Date Mon, 26 Dec 2011 15:26:43 GMT
Dne 25.12.2011 20:58, Peter Schuller napsal(a):
>>                 Read Count: 68844
> [snip]
>> why reported bloom filter FP ratio is not counted like this
>>>>> 10/68844.0
>> 0.00014525594096798558
> Because the read count is total amount of reads to the CF, while the
> bloom filter is per sstable. The number of individual reads to
> sstables will be higher than the number of reads to the CF (unless you
> happen to have exactly one sstable or no rows ever span sstables).
but reported ratio is  Bloom Filter False Ratio: 0.00495 which is higher 
than my computed ratio 0.000145. If you were true than reported ratio 
should be lower then mine computed from CF reads because there are more 
reads to sstables then to CF.

from investigation of bloom filter FP ratio it seems that default bloom 
filter FP ratio (soon user configurable) should be higher. Hbase 
defaults to 1% cassandra defaults to 0.000744. bloom filters are using 
quite a bit memory now.

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