[jira] [Resolved] (CASSANDRA-9830) Option to disable bloom filter in highest level of LCS sstables

["Paulo Motta (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/CASSANDRA-9830?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Paulo Motta resolved CASSANDRA-9830.
------------------------------------
       Resolution: Later
    Fix Version/s:     (was: 3.11.x)

> 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: lcs, performance
>
> 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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