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From Daniel Doubleday <>
Subject Re: High BloomFilterFalseRation
Date Wed, 27 Oct 2010 14:14:31 GMT
Hm -

not sure if I understand the random question. We are using RP. But I wouldn't know why that
should matter.
I thought that the bloom filter hash function should evenly distribute no matter what keys
come in.
Keys are '/' separated strings (aka paths :-))

I do bulk inserts like: (1000 rows at a time, with ~ 50 cols each)

	{'a/b/foo': cols},
	{'a/b/bar': cols},
	{'a/b/baz': cols}

and before that I would query for 'a/b'. Recursively as in mkdir -p

If parent paths are missing they would be inserted with the bulk insert.

The value for BloomFilterFalseRatio has been in the range of 0.19 - 0.59 in the last couple
of hours. Mostly around 0.3

We're on 0.6.6 btw

On Oct 27, 2010, at 3:58 PM, Jonathan Ellis wrote:

> This is not expected, no.  How random are your queries?  If you have a
> couple outlier rows causing the false positives that are being queried
> over and over then that could just be the luck of the draw.
> On Wed, Oct 27, 2010 at 5:24 AM, Daniel Doubleday
> <> wrote:
>> Hi people
>> We are currently moving our second use case from mysql to cassandra. While importing
the data (ongoing) I noticed that the BloomFilterFalseRation seems to be pretty high compared
to another CF which is in used in production right now.
>> Its a hierarchical data model and I cannot avoid to do a read before inserting multiple
>> I see a false positive ration of 0.28 while in my other CF it is 0.00025.
>> The CF has 5 live sstables whiel I read that ratio. At that time I inserted ~ 200k
rows with a total of 1M cols. Row keys are pretty large unfortunately (key.length() ~ 60)
>> Just wanted to check if this value is to be expected.
>> Thanks,
>> Daniel
> -- 
> Jonathan Ellis
> Project Chair, Apache Cassandra
> co-founder of Riptano, the source for professional Cassandra support

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