Mathematica & J/Link: Memory Constraints?

Question

I am doing a computing-intensive benchmark using Mathematica and its J/Link Java interface.

The benchmark grinds to a halt if a memory footprint of about 320 MB is reached, since this seems to be the limit and the garbage collector needs more and more time and will eventually fail.

The Mathematica function ReinstallJava takes the argument command line. I tried to do

ReinstallJava[CommandLine -> "java -Xmx2000m ..."]

but Mathematica seems to ignore the -Xmx option completely.

How can I set the -Xmx memory option for my java program? Where does the limit of 320 MB come from? Any help would be greatly appreciated.

Answer 1

ReinstallJava takes a JVMArguments option. You can use it to pass heap size like so:

In[1]:= Needs["JLink`"]

In[2]:= Options[ReinstallJava]

Out[2]= {ClassPath -> Automatic, CommandLine -> Automatic, 
 JVMArguments -> None, ForceLaunch -> False, Default -> Automatic, 
 CreateExtraLinks -> Automatic, "Asynchronous" -> Automatic}

In[3]:= ?JVMArguments

JVMArguments is an option to InstallJava that
allows you to specify additional command-line
arguments passed to the Java virtual machine at
startup. The string you specify is added to the
command line used to launch Java. You can use this
option to specify properties with the standard -D
syntax, such as "-Dsome.property=true". This
option is not supported on Mac OSX. >>

In[4]:= LoadJavaClass["java.lang.Runtime"];

In[5]:= java`lang`Runtime`getRuntime[]@maxMemory[]

Out[5]= 238616576

In[6]:= ReinstallJava[JVMArguments -> "-Xmx64g"];

In[7]:= LoadJavaClass["java.lang.Runtime"];

In[8]:= java`lang`Runtime`getRuntime[]@maxMemory[]

Out[8]= 61084008448

(I once figured this out in desperation by reading through the code in C:\Program Files\Wolfram Research\Mathematica\7.0\SystemFiles\Links\JLink\Kernel. After noticing it was listed in Options[ReinstallJava] it seemed kind of obvious…)