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From Peter Schuller <>
Subject Re: Dazed and confused with Cassandra on EC2 ...
Date Mon, 20 Sep 2010 17:26:32 GMT
> Nope - no swap enabled.

Something is seriously weird, unless the system clock is broken... Given:

INFO [GC inspection] 2010-09-20 15:27:42,046 (line
129) GC for ParNew: 325411 ms, 84284896 reclaimed leaving 640770336
used; max is 25907560448
 INFO [GC inspection] 2010-09-20 15:34:15,924 (line
129) GC for ParNew: 372272 ms, 82471240 reclaimed leaving 671616240
used; max is 25907560448

We have *extremely* slow ParNew:s on a heap that is not even close to
being full. I highly doubt fragmentation is causing this kind of

I wonder if it is possible that EC2 instances are over-committed on
memory such that swapping is happening behind the scenes on the
host... but I have always assumed memory was not over-committed on

Can you run with -XX:+PrintGC -XX:+PrintGCDetails -XX:+PrintGCTimestamps?

/ Peter Schuller

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