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Date: Thu, 5 Jan 2012 22:57:39 +0000 (UTC)
From: "Jonathan Ellis (Commented) (JIRA)" <jira@apache.org>
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Subject: [jira] [Commented] (CASSANDRA-3497) BloomFilter FP ratio should be
 configurable or size-restricted some other way
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    [ https://issues.apache.org/jira/browse/CASSANDRA-3497?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13180914#comment-13180914 ] 

Jonathan Ellis commented on CASSANDRA-3497:
-------------------------------------------

bq. We've found that many records that were inserted counld not be fetched in a multiget_slice query. It seemed as if the bloom filters resulted in false negatives.

I have trouble understanding how this could be the case, because if our BF could cause false negatives then surely we'd see that even at today's low default FP rates.  This patch didn't change how the BF is used, only the parameters it's created with, nor does it try to retrofit the new BF parameters onto existing sstables.

You did apply the v4 patch and not an earlier one, right?
                
> BloomFilter FP ratio should be configurable or size-restricted some other way
> -----------------------------------------------------------------------------
>
>                 Key: CASSANDRA-3497
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-3497
>             Project: Cassandra
>          Issue Type: New Feature
>          Components: Core
>            Reporter: Brandon Williams
>            Assignee: Yuki Morishita
>            Priority: Minor
>             Fix For: 1.0.7
>
>         Attachments: 0001-Add-bloom_filter_fp_chance-to-cli.patch, 0001-give-default-val-to-fp_chance.patch, 3497-v3.txt, 3497-v4.txt, CASSANDRA-1.0-3497.txt
>
>
> When you have a live dc and purely analytical dc, in many situations you can have less nodes on the analytical side, but end up getting restricted by having the BloomFilters in-memory, even though you have absolutely no use for them.  It would be nice if you could reduce this memory requirement by tuning the desired FP ratio, or even just disabling them altogether.

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