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From Tamar Fraenkel <>
Subject High CPU usage during repair
Date Sun, 10 Feb 2013 12:01:30 GMT
I run repair weekly, using a scheduled cron job.
During repair I see high CPU consumption, and messages in the log file
"INFO [ScheduledTasks:1] 2013-02-10 11:48:06,396 (line
122) GC for ParNew: 208 ms for 1 collections, 1704786200 used; max is
>From time to time, there are also messages of the form
"INFO [ScheduledTasks:1] 2012-12-04 13:34:52,406
(line 607) 1 READ messages dropped in last 5000ms"

Using opscenter, jmx and nodetool compactionstats I can see that during the
time the CPU consumption is high, there are compactions waiting.

I run Cassandra  version 1.0.11, on 3 node setup on EC2 instances.
I have the default settings:
compaction_throughput_mb_per_sec: 16
in_memory_compaction_limit_in_mb: 64
multithreaded_compaction: false
compaction_preheat_key_cache: true

I am thinking on the following solution, and wanted to ask if I am on the
right track:
I thought of adding a call to my repair script, before repair starts to do:
nodetool setcompactionthroughput 0
and then when repair finishes call
nodetool setcompactionthroughput 16

Is this a right solution?

*Tamar Fraenkel *
Senior Software Engineer, TOK Media

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