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From Jonathan Ellis <jbel...@gmail.com>
Subject Re: High BloomFilterFalseRation
Date Wed, 27 Oct 2010 14:28:15 GMT
Do you have a key "a/b" then?  What columns does it have?

On Wed, Oct 27, 2010 at 9:14 AM, Daniel Doubleday
<daniel.doubleday@gmx.net> wrote:
> 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
>> <daniel.doubleday@gmx.net> 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 columns.
>>>
>>> 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
>> http://riptano.com
>
>



-- 
Jonathan Ellis
Project Chair, Apache Cassandra
co-founder of Riptano, the source for professional Cassandra support
http://riptano.com

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