[
https://issues.apache.org/jira/browse/CASSANDRA-1181?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12882717#action_12882717
]
Jonathan Ellis commented on CASSANDRA-1181:
-------------------------------------------
it's expected that everything runs at normal priority w/o TPP, even as root.
normally, you would set TPP=1 to allow thread priorities to be set in the jvm.
the reason 42 is a trick is that the jvm will not let you set it to 1 if you
are not running as root, but the only reason you have to be root as far as
linux is concerned is to *raise* thread priority. lowering it is always ok.
so setting it to 42 fools the "is tpp 0" check on setPriority, without having
the jvm's excessively stringent santity-checking hose you.
source diving at
http://stackoverflow.com/questions/1662185/do-linux-jvms-actually-implement-thread-priorities
> kinder gentler compaction
> -------------------------
>
> Key: CASSANDRA-1181
> URL: https://issues.apache.org/jira/browse/CASSANDRA-1181
> Project: Cassandra
> Issue Type: Task
> Components: Core
> Reporter: Jonathan Ellis
> Assignee: Jonathan Ellis
> Fix For: 0.6.3
>
> Attachments: 1181.txt, 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.
--
This message is automatically generated by JIRA.
-
You can reply to this email to add a comment to the issue online.
