> > The JVM always reserves the maximum heap size as virtual space, but
> > does not allocate more of the heap than the current limit;
> the limit
> > will be adjusted up or down within the -Xms : -Xmx range as load
> > dictates. The unused virtual space is not available for
> any other use.
> >
> > Chuck, d'you happen to know how the virtual space
> reservation impacts
> > swap
> space requirements (if at all)? Although somewhat less
> unpleasant than buying RAM, 200 * 0.5Gbytes is still a lot of
> disk to allocate for swap if you expect it's never going to
> be used. I therefore assume there's not a direct mapping of
> reserved virtual space to reserved space in the swap file.
>
My server should be a good test case. We have 203 instances of java. 95%
of them are configured with -Xms64M -Xmx64M. A handful are configured
with higher values, but none with more than 256M.
A quick...
# ps axo rsz,vsz,comm,user|grep java|sort -n
..shows the java processes are consuming a total of 20GB of resident
memory and 56GB of virtual memory.
'top' shows zero swapping, by the way.
top - 08:24:57 up 128 days, 5:52, 5 users, load average: 1.31, 1.49,
1.40
Tasks: 424 total, 1 running, 422 sleeping, 0 stopped, 1 zombie
Cpu(s): 4.3%us, 1.1%sy, 0.0%ni, 93.6%id, 0.8%wa, 0.0%hi, 0.3%si,
0.0%st
Mem: 33265832k total, 22393776k used, 10872056k free, 297752k buffers
Swap: 2031608k total, 0k used, 2031608k free, 3961280k cached
--Eric
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