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From Vick Khera <>
Subject Re: performance tuning - where does the slowness come from?
Date Thu, 06 May 2010 17:49:44 GMT
On Thu, May 6, 2010 at 1:06 PM, Weijun Li <> wrote:
> In this case using mmap will cause Cassandra to use sometimes > 100G virtual
> memory which is much more than the physical ram, since we are using random
> partitioner the OS will be busy doing swap.

mmap uses the virtual address space to reference bits on the disk; it
does *NOT* use physical or virtual memory to copy that data other than
perhaps any disk buffer cache from reading the file (which you would
have anyhow).  Your memory usage tools will report high memory usage
because they tell you how much virtual address space you have

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