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From Edward Capriolo <edlinuxg...@gmail.com>
Subject Re: Bloom filters and LCS
Date Thu, 07 Mar 2013 21:48:23 GMT
I read that the change was made because Cassandra does not work well when
they are off. This makes sense because cassandra uses bloom filters to
decide if a row can be deleted without major compaction. However since LCS
does not major compact without bloom filters you can end up in cases where
rows never get deleted.

Edward

On Thu, Mar 7, 2013 at 4:30 PM, Wei Zhu <wz1975@yahoo.com> wrote:

> Where did you read that bloom filters are off for LCS on 1.1.9?
>
> Those are the two issues I can find regarding this matter:
>
> https://issues.apache.org/jira/browse/CASSANDRA-4876
> https://issues.apache.org/jira/browse/CASSANDRA-5029
>
> Looks like in 1.2, it defaults at 0.1, not sure about 1.1.X
>
> -Wei
>
> ----- Original Message -----
> From: "Michael Theroux" <mtheroux2@yahoo.com>
> To: user@cassandra.apache.org
> Sent: Thursday, March 7, 2013 1:18:38 PM
> Subject: Bloom filters and LCS
>
> Hello,
>
> (Hopefully) Quick question.
>
> We are running Cassandra 1.1.9.
>
> I recently converted some tables from Size tiered to Leveled Compaction.
>  The amount of space for Bloom Filters on these tables went down
> tremendously (which is expected, LCS in 1.1.9 does not use bloom filters).
>
> However, although its far less, its still using a number of megabytes.
>  Why is it not zero?
>
>
>                 Column Family: XXXX
>                 SSTable count: 526
>                 Space used (live): 7251063348
>                 Space used (total): 7251063348
>                 Number of Keys (estimate): 23895552
>                 Memtable Columns Count: 45719
>                 Memtable Data Size: 21207173
>                 Memtable Switch Count: 579
>                 Read Count: 21773431
>                 Read Latency: 4.155 ms.
>                 Write Count: 16183367
>                 Write Latency: 0.029 ms.
>                 Pending Tasks: 0
>                 Bloom Filter False Positives: 2442
>                 Bloom Filter False Ratio: 0.00245
>                 Bloom Filter Space Used: 44674656
>                 Compacted row minimum size: 73
>                 Compacted row maximum size: 105778
>                 Compacted row mean size: 1104
>
> Thanks,
> -Mike
>
>
>
>

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