Andre, Have a look at http://www.informit.com/guides/content.aspx?g=java&seqNum=253 for more details about JVM. A bit more difficult to read but with tons of info about JVM behaviour and default settings: http://java.sun.com/javase/technologies/hotspot/vmoptions.jsp
So for the SurvivorRatio the default setting is: -XX:SurvivorRatio=8 Ratio of eden/survivor space size [Solaris amd64: 6; Sparc in 1.3.1: 25; other Solaris platforms in 5.0 and earlier: 32] Hubert -----Original Message----- From: André Warnier [mailto:[EMAIL PROTECTED] Sent: 30 November 2008 15:54 To: Tomcat Users List Subject: Memory pool "Survivor space" Hi. I am monitoring a Tomcat during startup, using jconsole. This Tomcat's JVM is started with the switches "-Xms200M -Xmx200M", and it starts a rather heavy webapp that just about occupies Tomcat 100% during 5 minutes whenever I start it. (*) In the "memory" tab of jconsole, I observe that one of the display sections (Survivor space, the middle bar in the "Heap" section), has the following behaviour : - before the application is started, it remains constant at about 1 Mb - as soon as I start the application, it grows to about 2 MB, then drops down to 0, then grows up again to 2Mb, then drops to about 1 Mb, then back up again, etc.. The 2 Mb seems to be some kind of "hard limit", because it nevers goes over it. The "bottom" is more variable, sometimes between 1 Mb and 0, but more often 0. - when the application has finished loading (and Tomcat becomes responsive again), the amount of memory used by the Survivor space seems to stabilise again at 1.3 Mb, which is 0.3 Mb more than it was before the application started. Then it slowly over time drops down to 1 Mb. If the attachment survives this post, then you can see this graphically in it. If not, you can get a snapshot here : http://dev.dev.wissensbank.com/public/jconsole_survivor.png What I would like to know is : - what does this mean ? - where does the JVM get this apparent hard limit of 2 Mb for this pool size ? - does it matter ? I mean, assuming I could change it, would that have an impact in how the JVM works while starting this application, and how ? Below are three "cut and paste" of the summary display at the bottom left of jconsole when displaying this pool. 1) at some point during app startup Time: 2008-11-30 15:27:24 Used: 0 kbytes Committed: 2.240 kbytes Max: 2.240 kbytes 2) also during app startup Time: 2008-11-30 15:28:33 Used: 2.240 kbytes Committed: 2.240 kbytes Max: 2.240 kbytes 3) after app is started Time: 2008-11-30 15:34:32 Used: 1.306 kbytes Committed: 2.240 kbytes Max: 2.240 kbytes (*) to be completely precise : - if I use <load-on-startup> in the web.xml of this application (no matter with which value), then it seems to get started when Tomcat is started. Whenever that happens, Tomcat becomes unresponsive during approximately 5 minutes, using 95% of the machine's cpu time and not answering HTTP requests. At the end of these 5 minutes, Tomcat writes "server startup in .... ms" in its catalina.out file, and it becomes responsive again to HTTP requests. - if I do not have a <load-on-startup> tag in web.xml, then Tomcat prints "server startup in .... ms" in catalina.out, and becomes responsive in about 15 seconds (instead of 5 minutes). But then, it is when I first request the application in the browser that Tomcat becomes irresponsive during 5 minutes and uses 95% of cpu time during these 5 minutes. --------------------------------------------------------------------- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]
