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From Brian McEntire <>
Subject RE: Apache returning different sizes for same request [was Re: Controlling caching / session collision]
Date Mon, 10 Jan 2005 19:24:35 GMT
On Fri, 7 Jan 2005, Caldarale, Charles R wrote:

>> My browser requested listByOwner.jsp but received
>> decodedDataChartContents.jsp. I expected listByOwner
>> but saw decodedDataChartContents.
> One of the more common causes of this is inadvertent data sharing due to 
> applications that aren't thread-safe.  Examine the app code for 
> unprotected static fields, request-specific data stored in a session 
> object, etc.
> You should also try running the requests through Tomcat only (usually 
> port 8080 unless you've disabled the normal http connector) to see if 
> the problem stays with Tomcat or disappears when mod_jk is out of the 
> picture.

I'm the (poor :) sys admin and I don't know much Java but I can read it at 
a beginner level. I'm working with the developer of this application. He 
doesn't know threads well but doesn't think his application uses any. He 
also says the application does not make use of sessions.

Looking at one of the problematic JSP pages, I see (snippets):

<jsp:useBean id="state" class="postgres.PostgreSQLBean" scope="page" />
         ResultSet result;


         try {
                 if (state.isConnected())
                         result = state.executeQuery("SELECT owner_code 
FROM owner ORDER BY owner_code");
                 while ( {
<option value="<%= result.getString(1) %>"><%= result.getString(1) %>
         } catch (SQLException e) {
         } catch (Exception e) {

- - -

That's all the Java / tags on the whole page. Do you see anything wrong 
with the scope of the variables, threads, or sessions?

* The other question I have: Does anyone know of a simple way to make 
Tomcat log accesses in a format like Apache's Combined Log format?

I wrote test plans in JMeter and a PERL script which can monitor the 
Apache access log in real time and show the success and failure of each 
request-response through Apache and mod_jk (based on the results of served 
JSPs having known sizes.)

I left the default Tomcat port open (for internal use) on port 8080 and I 
can access the JSPs that are having problems directly though Tomcat. This 
eliminates mod_jk and Apache for troubleshooting. The only problem is, 
this is an intermittent problem so it very difficult to judge improvement 
with out JMeter and the test script which needs a combined access log as 

I'd be happy to share the PERL script with anyone interested. Contact me 
if you want it.


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