Weblogic5.1 VM goes to swap on startup

Question

I'm running Weblogic5.1 SP4 on Solaris7 64bit with the Sunsoft
JDK1.2.2-05a, I have 1Gig of memory installed, yet when I start a
weblogic VM with min heap size of 256M and a max heap size of 300M, it
immediately goes into swap space.
Memory: 1024M real, 821M free, 351M swap in use, 1506M swap free
Before starting the VM only 10M of swap is in use, and after starting
the VM as you see above, it appears that the VM hits swap immediately.
Anyone else notice this problem? How might I force the VM into physical
memory instead of swap?

Answer 1

Thanks for the links and pointers to utilities... I really appreciate having
learned something about investigating this further on my own.
Charlie Therit wrote:
Please make sure that you understand the complete meaning of the swap
numbers being reported. "/etc/swap -s" will show you the total amount of
swap space allocated (actually being used) and the amount reserved (pages
identified as anonymous memory that have not yet been backed by swap).
Even if you don't supply Solaris with any swapFS, the system will still
have and use swap space as Solaris swap space includes all allocated
swapFS partitions and available memory.
As long as the amount of allocated swap space (swap -s) doesn't exceed the
amount of disk space allocated for swap (swap -l), your system will have
the maximum use of its available RAM. If the amount allocated exceeds the
amount of swapFS then your system has begun locking pages in RAM and this
could lead to memory shortages. Paging should not be feared and is a
normal part of Solaris VM management. Unless the scan rate (vmstat 'sr'
column) reports higher than 300 in a 30 second period you aren't losing
performance because of memory management.
If you are interested in learning more about Solaris VM and swap
allocation, please read:
http://www.sunworld.com/swol-12-1997/swol-12-insidesolaris.html
and
http://www.sunworld.com/sunworldonline/swol-01-1998/swol-01-insidesolaris.html
Hope this helps,
Charlie
PS - If you really want to understand your JVM process, try using
/usr/proc/bin/pmap to view all segments, their sizes, and type. Also keep
in mind that each page in the JVM is backed by either anonymous memory
(swap) or the file system (UFS). Solaris reserves anonymous memory as the
process is created and allocates anonymous memory as the pages are
accessed and modified.
The views expressed in this posting are solely those of the author, and
BEA
Systems, Inc. does not endorse any of these views.
BEA Systems, Inc. is not responsible for the accuracy or completeness of
the
information provided and assumes no duty to correct, expand upon, delete
or update
any of the information contained in this posting.
Bryan O'Sullivan wrote:
w> Before starting the VM only 10M of swap is in use, and after
w> starting the VM as you see above, it appears that the VM hits swap
w> immediately.
I wouldn't come to this conclusion. The stats you are looking at tell
you how much swap is in use on the machine, not who's using it. You
should be using something else, such as ps, to see what the resident
set size of the java process is. That is the important number that
gives some indication of VM performance.
I would bet that idle processes are being swapped out on your system,
not the VM. If it turns out that those processes are not idle,
though, then you'll probably see bad performance as those processes
and the VM get into a food fight over who gets to be in physical
memory, with lots of thrashing.
<b