> 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 THIS COMMUNICATION MAY CONTAIN CONFIDENTIAL AND/OR OTHERWISE PROPRIETARY MATERIAL and is thus for use only by the intended recipient. If you received this in error, please contact the sender and delete the e-mail and its attachments from all computers. --------------------------------------------------------------------- To start a new topic, e-mail: users@tomcat.apache.org To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]