Learn about Java memory spaces?

Hi, I'm a student, and I need to do some research on and write a small paper about the "three or more Java memory spaces", what they do, how they differ.
The only problem is that spending a half hour searching google and reading quite a bit of documentation, I can't find any significant reference to or classification of these memory spaces! Can anyone provide me with a link to documentation that describes these memory spaces and their uses?
Thanks for your help!

Also
http://java.sun.com/products/hotspot/docs/whitepaper/Java_HotSpot_WP_Final_4_30_01.html
http://java.sun.com/developer/technicalArticles/Programming/turbo/ and the documents referenced at the end of the article
http://java.sun.com/docs/hotspot/gc1.4.2/faq.html
http://java.sun.com/docs/hotspot/gc5.0/gc_tuning_5.html
Thes will lead you to additional documentation.

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Hello!
I need to find info about java memory in JVM. What is :
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PS Old Gen
PS Perm Gen
PS Survivor Space
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PS Scavenge
regards - Marcin

user8672998 wrote:
Hello!
I need to find info about java memory in JVM. What is :
PS Eden Space
PS Old Gen
PS Perm Gen
PS Survivor Space
PS MarkSweep
PS Scavenge
regards - MarcinHi Marcin,
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Hi Guys,
I have a few questions about java memory management
Because i keep encounter a lot of out of memory error which i think java does not handle Vector/ArrayList re initialisation automatically
Asumme i have 2 million record in database and , i will process every 80000 and store it in Vector
while(true)
list = new Vector();
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Damm i should hacve read your post again
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while(true)
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i sugest moving the decleration outside the while loop:
list = new Vector();
while(true)
///rest of loop
} This could also be a problem
hope it help :-)
werns

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Message was edited by:
Woody.Benoty

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Hello,
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:)

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Installation Notes - JDK 5.0 Microsoft Windows (32-bit)
Your First Cup of Java
New to Java Center
The Java� Tutorial - A practical guide for programmers
The Java� Tutorial - Trail: Learning the Java Language
Java Programming Notes - Fred Swartz
How To Think Like A Computer Scientist
Introduction to Computer Science using Java
The Java Developers Almanac 1.4
Object-Oriented Programming Concepts
Object-oriented language basics
Don't Fear the OOP
Books:
The Java Programming Language - 4th Edition
Head First Java, by Bert Bates and Kathy Sierra
Thinking in Java (Free online), by Bruce Eckel
Core Java, by Cay Horstmann and Gary Cornell
Effective Java, by Joshua Bloch
http://java.sun.com/developer/Books/javaprogramming/
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~

High Eden Java Memory Usage/Garbage Collection

Hi,
I am trying to make sure that my Coldfusion Server is optomised to the max and to find out what is normal limits.
Basically it looks like at times my servers can run slow but it is possible that this is caused by a very old bloated code base.
Jrun can sometimes have very high CPU usage so I purchased Fusion Reactor to see what is going on under the hood.
Here are my current Java settings (running v6u24):
java.args=-server -Xmx4096m -Xms4096m -XX:MaxPermSize=256m -XX:PermSize=256m -Dsun.rmi.dgc.client.gcInterval=600000 -Dsun.rmi.dgc.server.gcInterval=600000 -Dsun.io.useCanonCaches=false -XX:+UseParallelGC -Xbatch ........
With regards Memory, the only memory that seems to be running a lot of Garbage Collection is the Eden Memory Space. It climbs to nearly 1.2GB in total just under every minute at which time it looks like GC kicks in and the usage drops to about 100MB.
Survivor memory grows to about 80-100MB over the space of 10 minutes but drops to 0 after the scheduled full GC runs. Old Gen memory fluctuates between 225MB and 350MB with small steps (~50MB) up or down when full GC runs every 10 minutes.
I had the heap set to 2GB initally in total giving about 600MB to the Eden Space. When I looked at the graphs from Fusion Reactor I could see that there was (minor) Garbage Collection about 2-3 times a minute when the memory usage maxed out the entire 600MB which seemed a high frequency to my untrained eye. I then upped the memory to 4GB in total (~1.2GB auto given to Eden space) to see the difference and saw that GC happened 1-2 times per minute.
Is it normal in Coldfusion that the Eden memory would grow so quickly and have garbage collection run so often? i.e do these graphs look normal?
Also should I somehow redistribute the memory available to give the Eden memory more since it seems to be where all the action is?
Any other advice for performance improvements would be much appreciated.
Note: These graphs are not from a period where jrun had high CPU.
Here are the graphs:
PS Eden Space Graph
PS Survivor Space Graph
PS Old Gen Graph
PS Perm Gen Graph
Heap Memory Graph
Heap/Non Heap Memory Graph
CPU Graph
Request Average Execution Time Graph
Request Activity Graph
Code Cache Graph

Hi,
>Is it normal in Coldfusion that the Eden memory would grow so quickly and have garbage collection run so often?
Yes normal to garbage collect Eden often. That is a minor garbage collection.
>Also should I somehow redistribute the memory available to give the Eden memory more since it seems to be where all the action is?
Sometimes it is good to set Eden (Eden and its two Survivor Spaces combined make up New or Young Generation part of JVM heap) to a smaller size. I know your thinking - what make it less, but I want to make it bigger. Give less a try (sometimes less = more, bigger not = better) and monitor the situation. I like to use -Xmn switch, some sources say to use other method/s. Perhaps you could try java.args=-server -Xmx4096m -Xms4096m -Xmn172m etc. I better mention make a backup copy of jvm.config before applying changes. Having said that now you know how you can set the size to bigger if you want.
I think the JVM is perhaps making some poor decisions with sizing the heap. With Eden growing to 1Gb then being evacuated not many objects are surviving and therefore not being promoted to Old Generation. This ultimately means the object will need to be loaded again latter to Eden rather than being referenced in the Old generation part of the heap. Adds up to poor performance.
>Any other advice for performance improvements would be much appreciated.
You are using Parallel garbage collector. Perhaps you could enable that to run multi-threaded reducing the time duration of the garbage collections, jvm args ...-XX:+UseParallelGC -XX:ParallelGCThreads=N etc where N = CPU cores (eg quad core = 4).
HTH, Carl.

Flash Builder 4.6 Java Heap Space Error

Hi,
I get this error "Java Heap Space" when trying to clean build (or build in any way) my project.
I have a lot of embeded assets (png, mp3 and some binary files embeded to be read as a ByteArray) which total about 37 MB. Including one more 1.6MB binary asset causes this error to occur.
I have tried to change my memory settings about (-Xmx and -Xms) as previous posts have suggested but this doesn't seem to make any difference.
Is there any patch or solution to this very frustrating limitation of Flash Builder?
Thanks for any help!
Tom

I constantly had issues with this. I managed to run into the max for increasing the heap space. I was able to get beyond the limit by flagging the FlashBuilder.exe file to allow it to allocate to higher memory address ranges. I'm on a 64 bit machine, so the only limitation was the 32 bit FlashBuilder process. Anyways i was able to get from 1024m up to 1720m. Also note that FlashBuilder 4.7 Beta is out and it is a native 64 bit application, so you will get higher addressing there. I just found it to be too buggy for my every day development tasks. Also missing the Design view really hurts development. I hope they put that back in.
Here's more detail on how I got beyond the java heap ceiling.
http://chrsmrtn.azurewebsites.net/flash-builder-java-heap-errors-limitations-of-xms-and-xm x/

OutOfMemoryError:Java Heap Space on JSP with %@page buffer % directive

Hi guys,
I am developing a large report requires a lot of memory using JSP, therefore I allocated about 4096kb in the JSP as follow:
==================================================================
<%@page contentType="text/html" pageEncoding="UTF-8"%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
"http://www.w3.org/TR/html4/loose.dtd">
<%@taglib uri="http://jakarta.apache.org/struts/tags-bean" prefix="bean" %>
<%@taglib uri="http://jakarta.apache.org/struts/tags-html" prefix="html" %>
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<%@page buffer="4096kb" %>
<html>...some work to display report ...</html>
==================================================================
The report runs fine but after few retrieves I got the OutOfMemoryError (OOME) and the only way for me to fix it is to restart the web server (tomcat). I went throught few troubleshooting tests and found out if I take out the <%@page buffer="4096kb" %> in the page, the error will go away regardless how much data I am retrieving from database (In another words, if I put this code into a report to retrieve a small data set, I will still get OOME after few tries). I know you can manually enlarge the Java Memory/Heap size, but it will not fix the problem as it will eventually run out of memory anyway. I am wondering is there known bugs relating to manually allocate buffer size for JSP pages? And how can i deal with it if it is a JSP "Bug"? Or there is something else I am doing wrong. (I have tried manually invoke System.gc() but it will not solve the problem)
any help is appreciated, Thanks.

Thanks for these information, you are truely amazing with amount of knowledge you have and your analytical skills.
Back to the topic:
<quote>
Only if you waste time with all the intermediate values that are also too big, and only if you persist in your illusion that you are buying performance with these huge buffers. You aren't. You are buying OutOfMemoryErrors instead.
You do need to realize that your output will be (i) buffered by the socket send buffer, which is only 8k on Windows, and (ii) transmitted in packets of the path MTU, which is less than 1500 bytes in most cases, so this huge buffer can't possibly do you any good - it just adds latency and OutOfMemoryError risk, as I've been telling you.
</quote>
I don't know which part of my replay does not agree with you that setting the buffer size too large is more of an problem other than a solution, perhaps I miss leaded you somehow.
<quote>That doesn't actually answer the question, does it?</quote>
Well if a page can be complied and retrieved in the first place, is there enough space to create the page/object? Perhaps you can tell me if I am wrong about it and why.
I believe the JspWriter object is stored in heap and heap is break up into few sections. I wouldn't be able to tell you for sure which section it resides but my guess is in Eden Space and that space is just about 4MB in space. But remeber I did my test by changing the buffer size to 2MB which is well under the 4MB, I still get the same error.
<quote>That was what your question was about. OutOfMemoryError using huge buffers. So that's what I focussed on.</quote>
Yes, you did ponting me out that but what you have done is told me not to use it, which I am very happy with. In my older post, I did actually correct myself and made my question more clear by asking
"Why with large JSP buffer size, the retrival of the JSP page chewing up the server memory? Shoudlnt memory be released after the page is retrieved?"
Unfortunitelly I don't think you pointing me anything about it, instead you told me all the reasons not to do it and assuming that I was arguing with you about "it is better to have large buffer jsp size". Again, sorry if I miss leaded you somehow.
Lets put it this way, even with large jsp buffer size (regardless whether we should be doing that or not) if the memory is freed properly, I will not get OOM error. Am I right?
<quote>I take out the <%@page buffer="4096kb" %> in the page, the error will go away</quote>
Yes, but I need to restart my server to make it work. I forgot to mention it, my bad.
Last, I finally found my answer through web and other forumes. The reason of this happening is because my web server did not release the PageContext object properly which JspWriter is linked to, therefore the memory does not get released at all. So ths the issue that chewing up the server memory. Again, thank you for all your help, your suggestion and knowledge did help me find out my answer in the end.

Java Heap Space Error

Hi,
We are running SAP MII 12.0 on windows server 2003 SP1 installed on a virtual machine with 4GB RAM, Intel Xenon CPU E5504 @ 2.00 GHz.
We started getting the Java Heap Space Error while executing a transaction which fetches about 200 rows. But now the error is quiet frequent and appears while trying to open or close the transactions or save trying to save data.
I have edited the heap space in the config tool to 2048 but this has not helped. Not sure if this is of significance but the SAP R3 server being used is quiet slow and takes about 3 mins to return data when I run the BAPI on it. This resulted in the transaction timing out a few times before we started getting the error. Increasing the connection timeout and read timeout for the transaction has not helped.
Please help me resolve this
Thanks
Maaz Ahmed

The BAPI being used is BAPI_GOODSMVT_GETITEMS I am specifying the Material, Plant, Goods Mvt ranges, and a date range.
I was informed that the QA R3 system is not among the best servers and the speeds would be better in production (under 3s).
Also I have been looking at the sapmmc. Each time I restart the cluster or the server I get a series of messages or alerts. In these alerts I see a series (Content, Navigation, PRT, etc..) of health checks failing. And the last two errors are as below
Object - Common Information
Attribute - Failed to Start Application
Description - 2 appl > 1 appl last reported value above threshold.
and
Object - Common Information
Attribute - Failed to Start Application
Description - 1 appl > 0 appl last reported value above threshold.
I am able to launch the menu page after this and when i run the above mantioned BAPI I get the error
Object - Memory Info
Attribute - Usage Rate
Description - 81% > 80% last reported value above threshold

Learn about Java memory spaces?

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