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From Jonathan Ellis <>
Subject Re: Load Balancing Mapper Tasks
Date Mon, 17 May 2010 04:53:05 GMT
On Sun, May 16, 2010 at 2:52 PM, Joost Ouwerkerk <> 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

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