Thanks Chuck,
I am using a 64-bit versions of the OS and JVM and I was confusing
virtual memory with RAM.
I have 8 GB of RAM and a 80 GB disc.
The commands -Xms3g -Xmx3g will set the min/max heap to 3 GB,please how
do I set the RAM for each instance of Tomcat5.5 to 2 GB
Regards
Peter
From: Peter Sparkes [mailto:[EMAIL PROTECTED]
Subject: Memory usage with multiple instances of tomcat
1. Does each tomcat instance use a separate 2 GB of memory, ie the 3
instance use 6 GB between them ?
2. or do they potentially share they same memory?
Don't confuse virtual memory with RAM. The heap allocations are
virtual, so there is no physical relationship with the amount of RAM you
have. (There are performance considerations, of course, in that if you
significantly oversubscribe RAM, you may suffer from excessive paging.)
One thing you've failed to mention is whether you're using 32- or 64-bit
versions of the OS and JVM. If 32-bit, then process virtual space is
typically limited to 2 GB, and the heap, code, and supporting libraries
must fit within that - you won't be able to allocate all 2 GB to the
heap. If you're running a 64-bit environment, the sky's the limit
(almost), and you could make each heap 256 GB, even with only 8 GB of
RAM (not recommended, due to aforementioned paging concerns).
Since each Tomcat runs as a separate process, there is no active sharing
of either heap or code across instances. However, if you're running a
client version of a current HotSpot JVM, there is some sharing of loaded
classes in the PermGen (other than static fields), primarily to reduce
startup time. You can see the shared amount in the Memory tab of
JConsole.
There is not currently any sharing in the server version of the HotSpot
JVM.
- Chuck
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