JConsole query

[Jess Holle <jessh (at) ptc.com>]

Darren Kukulka wrote:
> HI There, 
>
> Just a quick question regarding the JConsole tool we use to monitor Tomcat5 instances - 2 to be precise.
>
> We've noticed that within the Memory display window the breakdown of Heap usage shows three areas and their utilisation.  The descriptions of each space differs between the servers, even though essentially they are configured identically.
>
> They are both running Tomcat 5.5.15 on a Windows 2003 Server and differ slightly with their JVM (one is running the server JVM, the other is running the client JVM).
>  
> Server 1 - SUN JRE 1.5.0_06-b05 - shows "Eden", "Survivor" and "Tenured" space names
>
> Server 2 - SUN JRE 1.5.0_06-b05 - shows "PS Survivor", "PS Eden" and "PS Old Gen" space names.
>
> Can anybody explain this behaviour to me?
>   
You're getting different different generations because Java 5 is 
recognizing Server 2 as a server class machine -- due to heap 
allocation, total memory on the machine and such -- and it's not doing 
this on Server 1.

I must admit I'm a bit confused myself about when each occurs as the 
documented rules don't seem to actually quite be followed.

--
Jess Holle

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