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From "Jonathan Ellis (JIRA)" <j...@apache.org>
Subject [jira] Commented: (CASSANDRA-1181) kinder gentler compaction
Date Fri, 25 Jun 2010 15:40:51 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-1181?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12882612#action_12882612
] 

Jonathan Ellis commented on CASSANDRA-1181:
-------------------------------------------

to enable, add to cassandra.in.sh:

       -XX:+UseThreadPriorities \                                                        
         
        -XX:ThreadPriorityPolicy=42 \                                                    
          
        -Dcassandra.compaction_priority=1 \                                              
          

(TPP=42 is a workaround to allow us to *lower* thread priority without root privileges, explained
at http://tech.stolsvik.com/2010/01/linux-java-thread-priorities-workaround.html)

> kinder gentler compaction
> -------------------------
>
>                 Key: CASSANDRA-1181
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-1181
>             Project: Cassandra
>          Issue Type: Task
>            Reporter: Jonathan Ellis
>            Assignee: Jonathan Ellis
>             Fix For: 0.7
>
>         Attachments: CompactionManager.java
>
>
> I suggested this in a ML thread but it seems that nobody actually tried it.  I think
it's worth following up on:
> You could try setting the compaction thread to a lower priority.  You could add a thread
priority to NamedThreadPool, and pass that up from CompactionExecutor constructor.  According
to http://www.javamex.com/tutorials/threads/priority_what.shtml you have to run as root and
add a JVM option to get this to work.
> In particular, Brandon saw stress.py read latencies spike to 100ms during [anti]compaction
on a 2 core machine.  I'd like to see if this can mitigate that.

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