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From Jonathan Ellis <jbel...@gmail.com>
Subject Re: Config Maximum heap size for Cassandra
Date Thu, 28 Oct 2010 03:26:22 GMT
http://www.oracle.com/technetwork/java/javase/gc-tuning-6-140523.html

On Wed, Oct 27, 2010 at 9:30 PM, JKnight JKnight <beuknight@gmail.com> wrote:
> Could you tell me why Cassandra use memory more than needed?
>
>
> On Thu, Oct 28, 2010 at 9:15 AM, Nicholas Knight <nknight@runawaynet.com>
> wrote:
>>
>> Presumably you're on a 32-bit architecture (or at least a 32-bit JVM).
>> 32-bit processes won't be able to address more than "X" amount of memory,
>> where X would usually be >= 2GB, and < 4GB.
>>
>> The reason you can't use a full 4GB is that part of the address space is
>> necessarily reserved by the OS kernel. Exactly how much is reserved depends
>> on the OS, version thereof, and/or configuration, but at least 0.5-1GB is
>> usually a safe bet, so the behavior you see is exactly as expected.
>>
>> If your hardware is 64-bit, make sure you're running a 64-bit OS and a
>> 64-bit JVM. If you're stuck on 32-bit hardware that just happens to have
>> lots of RAM, you could run multiple Cassandra instances on each box..
>>
>> -NK
>>
>>
>> On Oct 28, 2010, at 10:04 AM, JKnight JKnight wrote:
>>
>> > Hi all,
>> >
>> > When I config Maximum heap size -Xmx4G, the memory will consume to 3.5G.
>> > When I call Perform GC (jconsole), the used memory reduce to 1G.
>> >
>> > When I config Maximum heap size -Xmx2G, Cassandra system run well.
>> >
>> > Is that Casandra problem?
>> > I want Cassandra use memory more effective. How can I do that?
>> >
>> > Thank a lot for support.
>> > --
>> > Best regards,
>> > JKnight
>>
>
>
>
> --
> Best regards,
> JKnight
>



-- 
Jonathan Ellis
Project Chair, Apache Cassandra
co-founder of Riptano, the source for professional Cassandra support
http://riptano.com

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