How Do I identify a Memory Leak?

Question

I know this is not enought information but...
My application used 3 hashtables in a Data object to store application data. I retrive this data from an XML file. I also download XML and merge it into andother XML file. Some of these hashtables contain object that contain more hashtables.
I am trying to use JProbe Profiler to find the leak. I notice the memory increases when I load the data into objects and put them into hash tables. I also notice an increase when I am merging newly downloaded XML into the current XML data. I am useing Nodelists and NOdes to get the data.
Does anyone have any tips or suggestion on how to find a memory leak?
Thank you,
Al

Answer 1

7 MB of XML file, loaded into a DOM? You realize, of
course, that DOMs are data structures that take up
memory, too, right?Yes I do. I load it into DOM then go through the Document and put the XML data into a custom file format (seialized objects). The data is sent from the server in the form of XML.
There's your problem. If you load X MB into memory
and keep it around as long as your application is
running, that's not necessarily a "leak". Yeah I realized this but it seems that if I load 7MB of my objects into hashtables my memory usage shouldn't increase by 30MB. I just assumed it would stay around 10MB.
The real issue is trading memory for CPU. If keeping
them in memory is crashing your app with OOM errors,
by all means just keep those objects in memory for as
long as you need them and then let the GC clean them
up. Don't put them in a Map, just let them have a
narrow method scope. Recreate them every time you
need them. Yes I'm beginning to see the light.
I'm sure you're thinking, "But recreating them will
cost CPU and slow down my app!" Yes, that's why it's
a tradeoff between memory and CPU.
Do you really need the whole document in memory at
once? If you're just cherry picking a few values out
of it, maybe you can use a SAX parser instead of a
DOM.
No I don't need all that data at once.
>
Either you're screwed or you need to rethink this.
You'd better hope that it's really not needed at
every moment for every client.After rethinking, I'm going to keep the serialized data in the file until I need it. Rather than searching through a hashtable for the object I want I will search the file.
What are your JVM settings for -Xms and -Xmx? Maybe
increasing those will do the trick.I did increase them and it helped a little, but I can still get a OutOfMemoryError if I try.
Are you sure these are the culprits? Have you
profiled the app to see if there are other sources of
leaks?Yes I have been profiling the application. It seems that there is a memory leek. I am just having trouble identifing it. I know the memory increases at 2 points. When I load the XML data into the DOM and when I load the DOM into my Custom object and then into the Hashtables.
Last resort? Buy more physical memory. It's cheap.I think I am going to keep unused data out of memory and access it form a file. After I make this change I think my memory usage will drop alot. I will profile again after I have this change made to see if there is a memory leak.
Thanks for you help,
Al