performance - java increase xmx dynamically at runtime

Question

I have a jvm server in my machine, now I want to have 2 apservers of mine sitting in same machine, however I want the standby one to have a really low amount of memory allocated with xmx because its passive, one the main server (active) goes down I want to allocate more memory to my passive server which is already up without restarting it (I have have them both having too much xmx - note they would consume memory at startup and I cant allow possibility of outOfMemory).

So I want passive - low xmx once active goes down I want my passive to receive much more xmx.

is there a way for me to achieve that. Thanks

Answer 1

It would be nice, but as far as I know it's not an option with the Sun provided JVMs.

The Xmx option is to specify maximum memory, it's there to prevent the JVM from consuming the entire machine's free memory. If you want to set it higher, it won't require the JVM allocate all of that memory. Why not just set it to a very high number and let the JVM grow into it over time?

To make sure your JVM doesn't start off with too little memory (creating lots of pauses as it grows the memory to the required size), adjust Xms to the size you want to allocate for the JVM at startup.