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Date: Wed, 30 Sep 2009 15:47:26 +0200
From: =?ISO-8859-15?Q?Christian_St=F6ber?=
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To: users@tomcat.apache.org
Subject: Memory behavior: Tomcat versus Jetty
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Hello list,

we are about to migrate our webserver cluster from Jetty 5.1.14 to 
Tomcat 6.0.20. Currently there are four servers in our cluster with 
simple load balancing and no session clustering.

At the moment we are testing Tomcat on 2 nodes of our cluster (also no 
session clustering yet). 2 remains with Jetty. Same WAR file an the same 
environment. Our first test ends in an OutOfMemoryError after two days. 
The java vm of the Tomcat servers has the same memory parameters as the 
server with the Jetty: -Xmx512m. And no other special GC parameters.

Apperently the Tomcat needs more memory than Jetty.

So we are trying to give Tomcat more memory: -Xmx768m. After two days 
the Tomcat is still running fine.

Obviously Tomcat needs just a little bit more memory than Jetty. After 
these two days we can state the following memory behavior.

Node   Mem used   Mem reserved
1 TC   400m       530m
2 TC   350m       495m
3 J    230m       350m
4 J    290m       400m

Averagely Tomcat is using round about 110m more memory than Jetty. But why?

I have seen that the Tomcat DefaultServlet may cache content up to 10m 
per default. But that are only 10m.
Are there some other things Tomcat may cache and Jetty does not?

Do you have any experiences?

Thanks in advance
Christian


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