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From JKnight JKnight <beukni...@gmail.com>
Subject Re: Config Maximum heap size for Cassandra
Date Thu, 28 Oct 2010 02:30:40 GMT
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

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