[ale] Can shmmax be set > total memory without harm?

[deritchie at gmail.com (David Ritchie)]

Do you have a swap device allocated for this VM? And are you really
using 4 GB of shared
memory, or just like having the number high?  I would expect this to
start paging early,
and the performance would be, ah, bad. And looking at this page

  http://www.centos.org/product.html

Given that you can't have a process size > 3 GB anyway, based on the
above link... and it unlikely that you are running two subsystems
with multibyte shared memory segments, I would recommend dropping this
down to something a bit more realistic, or get a VM with a gob more
memory...

what does "ipcs -m" show on the machine after the application has started?

What is top showing on the box when it is thrashing? Also, collecting
sar data might be a
good next step...  and strace/ltrace can be useful here to see if you
are spinning on a
system or library call... what is the application mix?

Just some thoughts....

-- Dave