Hi all,
I am having some serious performance issues with OGNL in my production
environment (Apache/Tomcat with Tapestry 4.1.3). I have also reproduced
the problem in a test environment using Tomcat with Tapestry 4.1.6. The
situation is related to the caching serialization question I had
earlier, but that question got no takers. Now that it has become an
issue for me in production, I am hoping this test case will generate
some advice from anyone who has already dealt with this.
As a simple test case I have two pages, SlowPage and FastPage. My
problem is that sometimes the fast page is blocked behind the slow
page. In my application I do have some actions that result in very long
hits (> 10 minutes). This is expected for that action, but it is not
expected that other hits become blocked by this single long running hit.
Here is my test case. See the code below. If I start Tomcat fresh and
open two different browsers, I can first hit SlowPage, then in the other
browser hit FastPage. The OGNL expression cache locks while evaluating
the expression on SlowPage, and does not release the lock to allow
FastPage to proceed until it is done. The result is that all un-cached
expressions are blocked for the duration. So, has anyone else run into
this? Is it a best practice to never put expensive operations as OGNL
expressions? That is unexpected, so I am still hoping that there is
another way around this problem. Note that if the experiment is
repeated the expression is not recompiled, I think. At least, the hits
are no longer blocked.
TestPage.java
public abstract class TestPage extends BasePage {
public String getSlowString() {
// ... cut here, wait 20 second
return "This takes at least 20 seconds to return";
}
public String getFastString() {
// no waiting here
return "This string is fast";
}
}
Then I have two simple pages, each using the TestPage class and having a
single Insert component:
SlowPage.page
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE page-specification PUBLIC
"-//Apache Software Foundation//Tapestry Specification 4.0//EN"
"http://tapestry.apache.org/dtd/Tapestry_4_0.dtd";>
<page-specification class="com.adaptiveplanning.ui.page.TestPage">
</page-specification>
SlowPage.html
<html>
<head><title>Slow Page</title></head>
<span jwcid="$content$">
<body>
<span jwcid="@Insert" value="ognl:slowString">Slow String</span>
</body>
</span>
</html>
FastPage.page
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE page-specification PUBLIC
"-//Apache Software Foundation//Tapestry Specification 4.0//EN"
"http://tapestry.apache.org/dtd/Tapestry_4_0.dtd";>
<page-specification class="com.adaptiveplanning.ui.page.TestPage">
</page-specification>
FastPage.html
<html>
<head><title>Fast Page</title></head>
<span jwcid="$content$">
<body>
<span jwcid="@Insert" value="ognl:fastString">Fast String</span>
</body>
</span>
</html>
Here is my earlier message, to continue the thread (from 2008-07-03):
Hi all,
I am struggling to understand what is going on with OGNL
compilation/caching in Tapestry 4.1.3.
My first question is regarding the caching of compiled OGNL
expressions. From my reading of the code it looks like the entire
application serializes through the ExpressionCacheImpl.java lock. What
am I missing? Doesn't that mean that if I have an expression that is
very expensive to evaluate that all other hits will be blocked with that
expression is evaluated? Or is that not what the compilation does? Has
anyone else experienced any performance problems that they can trace to
this locking/serialization?
My second question has been asked before on this list, but has not been
answered (I think). Why is a given OGNL expression evaluated multiple
times in a single instance? Is there any way to turn that off or work
around it?
I have been trying to dig into the source code to figure this out, but I
think I am getting lost in the details. Can someone please explain this
or point me at the information I need?
Thanks and regards,
Aaron
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