help with allocating more memory during runtime

[luc comeau]

Hey guys and girls. I recently had a post asking about a way to export data from a java program to an excel spreadsheet, which i successfully learned how to do. Now though i am running into a problem with a java out of memory exception when i go to finally write the excel file to the hard drive.

In the API for JXL which can be found here

keep in mind that you would need to download it to view it.

Anyways in this tutorial

the first question in the FAQ section talks about this problem with running out of memory when trying to generate large spreadsheets, which is the problem im having. I am trying to generate a spreadsheet with dimensions:
(row)(column): (10000)x(70)
the 10000 rows are double values.

I guess what i dont know about is how much memory to allocate to this process?
NOTE that i ran the process and it took two full days just to complete the 10000 iterations to get my data, and i got the exception when it tryed to write the excel file.

the FAQ gives an example, but i dont want to give it too much memory infear of it crashing my system midway through the tests or anything.So does anyone have any idea of how i could come up with th right amount of memory to allocate for this process.

I'll paste the faq since it isnt long:

    
 By default a JVM places an upper limit on the amount of memory available to the current process in order to prevent runaway processes gobbling system resources and making the machine grind to a halt. When reading or writing large spreadsheets, the JVM may require more memory than has been allocated to the JVM by default - this normally manifests itself as a java.lang.OutOfMemory exception.
 
For command line processes, you can allocate more memory to the JVM using the -Xms and -Xmx options eg. to allocate an initial heap allocation of 10 mB, with 100 mB as the upper bound you can use
 
    java -Xms10m -Xmx100m -classpath jxl.jar spreadsheet.xls 

i hope this is enough information, any tips or help from the experts would be awesome! thanks

[Ernest Friedman-Hill]

You won't crash your system by giving Java too much memory unless you've got bad memory chips. If you've got a memory-intensive application, then make the heap as big as you can get away with -- start with 3/4 of physical RAM and see how that works out.

[luc comeau]

so make the upper bound 3/4 of my RAM? Im going to assume yes, what about the lower bound?

I wish the damm thing didn't take so long to complete its iteration before it tells me it runs out of memory!I'm so strap for time i really can't afford to goof around with guessing how much memory to give the heap, but i guess its my only option. Hopefully it works, thanks for your reply Ernest
-Luc