Please help :: JVM Memory Calculation

Question

Hi Guys,
I've developed a struts based web application. I've got the java.lang.OutOfMemoryError when I tried to retrieve 2000 records in the login page itself. Ofcourse even in my listing of the modules.. i am getting the same...error
still i have confused with JVM size.. how much to be increased...? presently i have JVM size 32MB with jdk1.5, tomcat 5.5 , linux os..with 1GB RAM
please suggest..,

Answer 1

Well firstly i feel Holding 2000 records at a time is ceratinly foolish as sooner or later it would eat up all your JVM heap...
A better solution in order to maintain this is to use data paging....
first....
which you might divde into pages....
Say for example....
select count(*) from table_name where <condition>gives you total number of records present.
Say if you have divded the total records into 100 per Virtual Page
at a strench fetch first 100 records using properties like rownum(oracle),LIMIT clause in mysql and etc.
Hold the present page pointers in a bean Scoped session and then fetch the other page accordingly.this saves a lot of memory thought their is a lot of overhead involved.
the other would be usage of other caching techniques.
May be the below article might help you in this regard
http://java.about.com/library/weekly/uc_querycache1.htm
And if you are still struck to increasing increasing JVM Size you might have to configure it in App server batch server runtime parameters
check out below article of how configure few app servers to increase JVM Heap
http://www.chemaxon.com/jchem/doc/admin/tomcat.html
http://www.redhat.com/docs/manuals/jboss/jboss-eap-4.2/doc/Server_Configuration_Guide/ch02s02s02.html
http://e-docs.bea.com/wls/docs81/perform/JVMTuning.html
http://www.ibm.com/developerworks/websphere/library/techarticles/0706_sun/0706_sun.html
and checkout the below article to findout different technique followed to solve memory leak problems.
http://support.bea.com/application_content/product_portlets/support_patterns/wls/InvestigatingOutOfMemoryMemoryLeakProblemsPattern.html
Hope this might help :)
REGARDS,
RaHuL