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https://issues.apache.org/jira/browse/CASSANDRA-6142?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13796515#comment-13796515
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Marcus Eriksson commented on CASSANDRA-6142:
--------------------------------------------

CompactionsPurgeTest fails:
{noformat}
    [junit] Testsuite: org.apache.cassandra.db.compaction.CompactionsPurgeTest
    [junit] Tests run: 6, Failures: 2, Errors: 0, Skipped: 0, Time elapsed: 
9.365 sec
    [junit] 
    [junit] Testcase: 
testMinTimestampPurge(org.apache.cassandra.db.compaction.CompactionsPurgeTest): 
  FAILED
    [junit] expected:<2> but was:<1>
    [junit] junit.framework.AssertionFailedError: expected:<2> but was:<1>
    [junit]     at 
org.apache.cassandra.db.compaction.CompactionsPurgeTest.testMinTimestampPurge(CompactionsPurgeTest.java:185)
    [junit] 
    [junit] 
    [junit] Testcase: 
testCompactionPurgeTombstonedRow(org.apache.cassandra.db.compaction.CompactionsPurgeTest):
        FAILED
    [junit] expected:<10> but was:<5>
    [junit] junit.framework.AssertionFailedError: expected:<10> but was:<5>
    [junit]     at 
org.apache.cassandra.db.compaction.CompactionsPurgeTest.testCompactionPurgeTombstonedRow(CompactionsPurgeTest.java:313)
    [junit] 
    [junit] 
    [junit] Test org.apache.cassandra.db.compaction.CompactionsPurgeTest FAILED
{noformat}
and a few nits:
in LazilyCompactedRow:
* make reducer and merger final
* remove comment about reducer being null on row 123


> Remove multithreaded compaction
> -------------------------------
>
>                 Key: CASSANDRA-6142
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-6142
>             Project: Cassandra
>          Issue Type: Bug
>          Components: Core
>            Reporter: Jonathan Ellis
>            Assignee: Jonathan Ellis
>            Priority: Minor
>             Fix For: 2.1
>
>
> There is at best a very small sweet spot for multithreaded compaction 
> (ParallelCompactionIterable).  For large rows, we stall the pipeline and fall 
> back to a single LCR pass.  For small rows, the overhead of the coordination 
> outweighs the benefits of parallelization (45s to compact 2x1M stress rows 
> with multithreading enabled, vs 35 with it disabled).



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