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From JMons...@gkservices.com
Subject RE: Question about the "compress" setting MIME-Version: 1.0
Date Sat, 09 Sep 2006 17:38:00 GMT
We're using the latest jdk 1.5 release (the server version of the JVM) and 
currently do have the heap min/max set to 1024 . I'll try the other jvm 
options related to GC. I know we tried -Xincgc to no effect. 

 We are indeed seeing OutofMemoryExceptions, but at this point the app has 
a few other problems, that I don't believe are related to the compression, 
so the logfiles are pretty confusing (and the app is catching most 
Exceptions, and only printing the message of the exception, not the 
stacktrace).  What is stumping me a bit is that Tomcat flat out dies with 
no conclusive messages in the logs. My best theory so far is that the Gzip 
filter I mentioned below may be allocating at least 4 objects, each with a 
copy of the entire (compressed) response. Each request is grabbing 100K 
increments of a larger file, but the files can get somewhat large (2-3M) 
The filter is basically a SerlvetOutputStream that passes all the writes 
to the GZIPOutputStream which is wrapping a ByteArrayOutputStream. When 
the ServletOutputStream is closed, it gets the byte array from the 
ByteArrayOutputStream, converts it to a String, and writes it to the 
original HttpResponse. This is probably running down the free memory in 
the JVM pretty quickly, causing the gc to run not only frequently while 
the server is under heavy strain, but also each time it is freeing up alot 
of memory.

That's why I'm very curious to find out in greater detail exactly how the 
"compress" option is working. I'll take a look at the code again as well, 
but if anyone has any experience using the filter from the O'Reilly  book 
(this is the second time I've seen it used in apps), and in particular how 
the Tomcat implementation behaves, I'd greatly appreciate it. 

 



"Derrick Koes" <Derrick_Koes@skillsoft.com> 
09/09/2006 08:10 AM
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Subject
RE: Question about the "compress" setting MIME-Version: 1.0







Sounds like a bandwidth/throughput problem if you are concerned with the
connector compression attribute.  You may want to try some performance
tuning with the throughput garbage collector.

Assuming your problem is an OutOfMemory Error and at least Java 1.4.1,
try the following VM settings
-Xmn=1024m
-Xmx=1024m
-XX:+AggressiveHeap
-XX:+UseParallelGC
-XX:MaxPermSize=128m

Below is reference documentation.

http://java.sun.com/docs/hotspot/gc1.4.2/
http://java.sun.com/j2se/1.4.2/1.4.2_whitepaper.html

If you still have memory problems, try a memory profiler like Jprofiler
to detect memory leaks as well as CPU issues.
http://www.ej-technologies.com/products/jprofiler/overview.html

It would be helpful if you posted any errors in the log files when you
incur the issue.

-----Original Message-----
From: JMonstad@gkservices.com [mailto:JMonstad@gkservices.com] 
Sent: Saturday, September 09, 2006 1:33 AM
To: users@tomcat.apache.org
Subject: Question about the "compress" setting MIME-Version: 1.0

We currently have an app in prod using the original servlet filer
described at
http://www.onjava.com/pub/a/onjava/2003/11/19/filters.html?page=3  , and
I know  from the comments to the article in the link that there may be
some issues with it. My question is; how does the built-in tomcat
implementation, which is activated by the compress="true" attribute on
the default http1.1 connector improve on the servlet filter mentioned
above. For context, I should mention that  we're running on Windows 2003
server, sp1 using Apache Tomcat/5.0.28 on on dual Intel Xeon processor
with 4Gb of RAM. 
Under various memory settings ranging from giving the heap from any
interval of  800 - 1500 MB of heap space, the Tomcat server will die
more or less silently under even moderate load (heavy load kills it
almost immediately).
Any help would be appreciated, and as I've mentioned (username jmonstad)
on the IRC channel, I may be willing to entertain engagements from local
to Minneapolis, US gurus for $'s 

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