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From Yang <>
Subject Re: release mmap memory through jconsole?
Date Fri, 30 Sep 2011 17:09:50 GMT

I thought bigger young gen would allow more objects to die (become
non-reachable) before  minor collection, so the minor collection cost
is low. particularly it would allow you to merge more updates and not
consume memory (since old objects are released on GC)

bigger old gen would allow you to accumulate more rows into your
memtable, so you can avoid
later compaction cost.

if not giving it to heap, then it's a choice between os buffer and
cassandra row cache. I think row cache is definitely better since you
avoid the cost of serializing/deserializing; well this is assuming
that your access pattern is random though, otherwise OS cache has the
benefit of spacial locality (it loads blocks at once instead of a
single row).


2011/9/30 Norman Maurer <>:
> I would also not use such a big heap. I think most people will tell
> you that 12G -16G is max to use.
> Bye,
> Norman
> 2011/9/30 Yi Yang <>:
>> It is meaningless to release such memory. The counting includes the data you reached
in the SSTable. Those data locates on your hard drive. So it is not the RAM spaces you have
actually used.
>> -Y.
>> ------Original Message------
>> From: Yang
>> To:
>> ReplyTo:
>> Subject: release mmap memory through jconsole?
>> Sent: Oct 1, 2011 12:40 AM
>> I gave an -Xmx50G to my Cassandra java processs, now "top" shows its
>> virtual memory address space is 82G, is there
>> a way to release that memory through JMX ?
>> Thanks
>> Yang
>> 從我的 BlackBerry(R) 無線裝置

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