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From Peter Schuller <peter.schul...@infidyne.com>
Subject Re: Cassandra committing massive virtual memory
Date Thu, 22 Jul 2010 10:24:14 GMT
> We are seeing cassandra using very high virtual memory. One server in the
> cluster shows 90GB and the other shows about 70GB of committed virtual
> memory.
> The real memory used is less than 1GB. The Xmx is 4GB. The physical memory
> on the machine is 32GB and the swap space on the machine is around 20GB.
>
> I understand that the virtual memory is not really used by the process and
> is just reserved. My question is why does cassandra need to reserve such
> huge memory. What is the logic that is used internally. How is it related to
> usage pattern or data storage pattern. Should we be concerned?

Virtual size in and of itself is not a concern because it is mmap():ed
address space. AFAIK you may see sizes up to the entire database size.

What people have had issues with is swapping resulting from the
operating system considering mmap():ed area contributing to memory
pressure and swapping out the Java heap. But unless you have issues
like that, I don't believe the virtual address space size in and of
itself should be a concern.

-- 
/ Peter Schuller

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