This was my first thought, too. We switched to mmap_index_only and
didn't see any change in behavior. Looking at the smaps file attached
to my original post, one can see that the mmapped index files take up
only a minuscule part of RSS.

On Wed, May 4, 2011 at 11:37 PM, Oleg Anastasyev <oleganas@gmail.com> wrote:
> Probably this is because of mmapped io access mode, which is enabled by default
> in 64-bit VMs - RAM is occupied by data files.
> If you have such a tight memory reqs, you can turn on standard access mode in
> storage-conf.xml, but dont expect it to work fast then:
> <!--
>
>
>  ~ Access mode.  mmapped i/o is substantially faster, but only practical on
>
>
>  ~ a 64bit machine (which notably does not include EC2 "small" instances)
>
>
>  ~ or relatively small datasets.  "auto", the safe choice, will enable
>
>
>  ~ mmapping on a 64bit JVM.  Other values are "mmap", "mmap_index_only"
>
>
>  ~ (which may allow you to get part of the benefits of mmap on a 32bit
>
>
>  ~ machine by mmapping only index files) and "standard".
>
>
>  ~ (The buffer size settings that follow only apply to standard,
>
>
>  ~ non-mmapped i/o.)
>
>
>  -->
>
>
>  <DiskAccessMode>standard</DiskAccessMode>
>
>