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Date: Tue, 4 Oct 2011 19:45:34 +0000 (UTC)
From: "Brandon Williams (Created) (JIRA)" <jira@apache.org>
To: commits@cassandra.apache.org
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Subject: [jira] [Created] (CASSANDRA-3308) Add compaction_thread_priority
 back
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Add compaction_thread_priority back
-----------------------------------

                 Key: CASSANDRA-3308
                 URL: https://issues.apache.org/jira/browse/CASSANDRA-3308
             Project: Cassandra
          Issue Type: Bug
            Reporter: Brandon Williams
             Fix For: 1.0.0


In CASSANDRA-3104, this was removed with the following reasoning:

bq. compaction_throughput_mb_per_sec is a more effective throttle on compaction.

This turns out to be false in the majority of deployments.  In many (if not most) situations, compaction is actually CPU bound, not IO bound, so multithreaded compaction is generally helpful, but the priority needs to be lowered in order to prevent it from stealing CPU used for reads/writes.

Compaction is always CPU bound on both real hardware (sw raid0 with two SATA disks) and on a rackspace cloud server (though my understanding is they are back by a raid10 array underneath) however I suspect even a single drive is fast enough to handle the ~20MB/s that compaction is currently performing when unthrottled.

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