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From "Paulo Motta (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-9830) Option to disable bloom filter in highest level of LCS sstables
Date Wed, 30 Mar 2016 17:47:25 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-9830?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15218434#comment-15218434
] 

Paulo Motta commented on CASSANDRA-9830:
----------------------------------------

Thanks for spotting this, it seems I overlooked this case. Even though there is an anticompaction
test, it moves sstables to the same level in the repaired set so it does not check this case.

I will update it to cover this case. The basic idea is to regenerate BF if dropping to level
0 during anti-compaction with this setting enabled.

> Option to disable bloom filter in highest level of LCS sstables
> ---------------------------------------------------------------
>
>                 Key: CASSANDRA-9830
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-9830
>             Project: Cassandra
>          Issue Type: New Feature
>          Components: Compaction
>            Reporter: Jonathan Ellis
>            Assignee: Paulo Motta
>            Priority: Minor
>              Labels: performance
>             Fix For: 3.x
>
>
> We expect about 90% of data to be in the highest level of LCS in a fully populated series.
 (See also CASSANDRA-9829.)
> Thus if the user is primarily asking for data (partitions) that has actually been inserted,
the bloom filter on the highest level only helps reject sstables about 10% of the time.
> We should add an option that suppresses bloom filter creation on top-level sstables.
 This will dramatically reduce memory usage for LCS and may even improve performance as we
no longer check a low-value filter.
> (This is also an idea from RocksDB.)



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