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From Joost Ouwerkerk <jo...@openplaces.org>
Subject Re: Load Balancing Mapper Tasks
Date Mon, 17 May 2010 14:42:08 GMT
At any given moment at least half of those threads are in the following
state; what does it represent?

Name: ROW-READ-STAGE:6
State: WAITING on
java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject@fea6030
Total blocked: 44  Total waited: 479

Stack trace:
sun.misc.Unsafe.park(Native Method)
java.util.concurrent.locks.LockSupport.park(LockSupport.java:158)
java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(AbstractQueuedSynchronizer.java:1925)
java.util.concurrent.LinkedBlockingQueue.take(LinkedBlockingQueue.java:358)
java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:947)
java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:907)
java.lang.Thread.run(Thread.java:619)


On Mon, May 17, 2010 at 12:53 AM, Jonathan Ellis <jbellis@gmail.com> wrote:

> On Sun, May 16, 2010 at 2:52 PM, Joost Ouwerkerk <joost@openplaces.org>
> wrote:
> > Meanwhile. I'm still getting TimedOutException errors when mapping this
> > 30-million row table, even when retrieving no data at all.  It looks like
> it
> > is related to disk activity on "hot" nodes (when the same cassandra node
> has
> > to handle many concurrent requests for adjacent range slices).  Using 0.7
> > trunk branch doesn't appear to alleviate it.  CPU load is at about 25%
> when
> > this happens.  Is there some kind of synchronization that might prevent
> the
> > same file from being scanned by multiple threads?
>
> No, but there's only `concurrent_reads` threads serving reads and if
> you have a lot of ops in the queue ahead of you then that would do it.
>  (pending tasks in row stage under cassandra.concurrent jmx.)
>
> --
> Jonathan Ellis
> Project Chair, Apache Cassandra
> co-founder of Riptano, the source for professional Cassandra support
> http://riptano.com
>

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