interesting. Actually it's using a soft reference. What if you substitute
_oldSerializedViews = new ReferenceMap();
by
_oldSerializedViews = new ReferenceMap(AbstractReferenceMap.WEAK,
AbstractReferenceMap.WEAK, true);
?
I'm curious if the behaviour is still the same.
Thomas
On 6/4/07, André Næss <[EMAIL PROTECTED]> wrote:
Hi
We are working on a JSF project and recently started stress testing the
system. This stress-testing caused the JVM to run out of memory and
spend most of it time doing Full GC. Analyzing the heap revealed that
most of the memory was being retained by SerializedViewCollection
instances. We also noticed that the value of NUMBER_OF_VIEWS_IN_SESSION
didn't seem to affect the memory usage.
I then decided to have a look at the code, and found something very
interesting at line 614 in JspStateManagerImpl. When views are taken out
of the main collection they are stuffed into the _oldSerializedViews
collection which is supposed to be a weak hashmap. The idea here, I
suppose, is to use this as a kind of cache which trades some extra
memory for performance, but only if the memory is available.
Unfortunately it doesn't seem like this works as the author expected
when he wrote this:
// old views will be hold as soft references which will be
removed by
// the garbage collector if free memory is low
The problem we saw when profiling was the the OldGen would grow and grow
and reach a plateau, at which point the GC wasn't able to clean anything
out if it. I removed the usage of the _oldSerializedViews and this
immediately improved the situation. When the OldGen maxes out, a full GC
is executed which reclaims most of the data. I've successfully tested
this using JMeter, with up to 2000 threads running at a constant load of
30 requests per second, and it seems fine.
Unless the _oldSerializedViews object can be made to work properly, I
think it should be removed. After all, the developers can control the
memory in a more predictable manner using the NUMBER_OF_VIEWS_IN_SESSION
parameter. However, it is not entirely clear to me what the purpose of
storing the views in the SerializedViewsCollections really is? Is it
purely a performance trick (providing better rendering times), or does
it provide some other kind of advantage to the end user?
André Næss
Here's the svn diff output:
~/code/myfaces-1.1.5/impl/src/main/java/org/apache/myfaces/application/jsp$
svn diff
Index: JspStateManagerImpl.java
===================================================================
--- JspStateManagerImpl.java (revision 543859)
+++ JspStateManagerImpl.java (working copy)
@@ -41,6 +41,7 @@
import javax.faces.render.ResponseStateManager;
import java.io.*;
import java.util.*;
+import java.util.logging.Logger;
import java.util.zip.GZIPInputStream;
import java.util.zip.GZIPOutputStream;
@@ -611,7 +612,7 @@
// old views will be hold as soft references which will be
removed by
// the garbage collector if free memory is low
- private transient Map _oldSerializedViews = null;
+// private transient Map _oldSerializedViews = null;
public synchronized void add(FacesContext context, Object state) {
Object key = new SerializedViewKey(context);
@@ -623,10 +624,10 @@
int views = getNumberOfViewsInSession(context);
while (_keys.size() > views) {
key = _keys.remove(0);
- Object oldView = _serializedViews.remove(key);
- if (oldView != null) {
- getOldSerializedViewsMap().put(key, oldView);
- }
+ _serializedViews.remove(key);
+// if (oldView != null) {
+// getOldSerializedViewsMap().put(key, oldView);
+// }
}
}
@@ -663,19 +664,19 @@
/**
* @return old serialized views map
*/
- protected Map getOldSerializedViewsMap() {
- if (_oldSerializedViews == null) {
- _oldSerializedViews = new ReferenceMap();
- }
- return _oldSerializedViews;
- }
+// protected Map getOldSerializedViewsMap() {
+// if (_oldSerializedViews == null) {
+// _oldSerializedViews = new ReferenceMap();
+// }
+// return _oldSerializedViews;
+// }
public Object get(Integer sequence, String viewId) {
Object key = new SerializedViewKey(viewId, sequence);
Object value = _serializedViews.get(key);
- if (value == null) {
- value = getOldSerializedViewsMap().get(key);
- }
+// if (value == null) {
+// value = getOldSerializedViewsMap().get(key);
+// }
return value;
}
}
--
http://www.irian.at
Your JSF powerhouse -
JSF Consulting, Development and
Courses in English and German
Professional Support for Apache MyFaces
