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https://issues.apache.org/jira/browse/CASSANDRA-3234?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13109702#comment-13109702
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Jonathan Ellis commented on CASSANDRA-3234:
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bq. that's probably not optimal for LeveledCompaction
Can you elaborate?
> LeveledCompaction has several performance problems
> --------------------------------------------------
>
> Key: CASSANDRA-3234
> URL: https://issues.apache.org/jira/browse/CASSANDRA-3234
> Project: Cassandra
> Issue Type: Bug
> Components: Core
> Affects Versions: 1.0.0
> Reporter: Jonathan Ellis
> Assignee: Jonathan Ellis
> Fix For: 1.0.0
>
> Attachments: 0001-optimize-single-source-case-for-MergeIterator.txt,
> 0002-add-TrivialOneToOne-optimization.txt,
> 0003-fix-leveled-BF-size-calculation.txt,
> 0004-avoid-calling-shouldPurge-unless-necessary.txt,
> 0005-use-Array-and-Tree-backed-columns-in-compaction-v2.patch,
> 0005-use-Array-and-Tree-backed-columns-in-compaction.txt
>
>
> Two main problems:
> - BF size calculation doesn't take into account LCS breaking the output apart
> into "bite sized" sstables, so memory use is much higher than predicted
> - ManyToMany merging is slow. At least part of this is from running the full
> reducer machinery against single input sources, which can be optimized away.
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