AppEngine JRuby - OutOfMemoryError: Java heap space - can it be solved?

I use AppEngine JRuby on Rails (SDK version 1.3.3.1) - a problem I encounter often is that after a few requests the server is getting really SLOW, until it dies and throws OutOfMemoryError on the terminal (OSX).

The requests themselves are very lightweight, not more than looking for an entity or saving it, using DataMapper.

On appspot, this problem is not happening.

Is there any way to enlarge the heap space for JRuby?

The exception log:

    Exception in thread "Timer-2" java.lang.OutOfMemoryError: Java heap space
Apr 29, 2010 8:08:22 AM com.google.apphosting.utils.jetty.JettyLogger warn
WARNING: Error for /users/close_users
java.lang.OutOfMemoryError: Java heap space
    at org.jruby.RubyHash.internalPut(RubyHash.java:480)
    at org.jruby.RubyHash.internalPut(RubyHash.java:461)
    at org.jruby.RubyHash.fastASet(RubyHash.java:837)
    at org.jruby.RubyArray.makeHash(RubyArray.java:2998)
    at org.jruby.RubyArray.makeHash(RubyArray.java:2992)
    at org.jruby.RubyArray.op_diff(RubyArray.java:3103)
    at org.jruby.RubyArray$i_method_1_0$RUBYINVOKER$op_diff.call(org/jruby/RubyArray$i_method_1_0$RUBYINVOKER$op_diff.gen)
    at org.jruby.runtime.callsite.CachingCallSite.call(CachingCallSite.java:146)
    at org.jruby.ast.CallOneArgNode.interpret(CallOneArgNode.java:57)
    at org.jruby.ast.LocalAsgnNode.interpret(LocalAsgnNode.java:123)
    at org.jruby.ast.NewlineNode.interpret(NewlineNode.java:104)
    at org.jruby.ast.BlockNode.interpret(BlockNode.java:71)
    at org.jruby.runtime.InterpretedBlock.evalBlockBody(InterpretedBlock.java:373)
    at org.jruby.runtime.InterpretedBlock.yield(InterpretedBlock.java:346)
    at org.jruby.runtime.InterpretedBlock.yield(InterpretedBlock.java:303)
    at org.jruby.runtime.Block.yield(Block.java:194)
    at org.jruby.RubyArray.collect(RubyArray.java:2354)
    at org.jruby.RubyArray$i_method_0_0$RUBYFRAMEDINVOKER$collect.call(org/jruby/RubyArray$i_method_0_0$RUBYFRAMEDINVOKER$collect.gen)
    at org.jruby.runtime.callsite.Cachi开发者_开发知识库ngCallSite.callBlock(CachingCallSite.java:115)
    at org.jruby.runtime.callsite.CachingCallSite.call(CachingCallSite.java:122)
    at org.jruby.ast.CallNoArgBlockNode.interpret(CallNoArgBlockNode.java:64)
    at org.jruby.ast.CallNoArgNode.interpret(CallNoArgNode.java:61)
    at org.jruby.ast.LocalAsgnNode.interpret(LocalAsgnNode.java:123)
    at org.jruby.ast.NewlineNode.interpret(NewlineNode.java:104)
    at org.jruby.ast.BlockNode.interpret(BlockNode.java:71)
    at org.jruby.ast.EnsureNode.interpret(EnsureNode.java:98)
    at org.jruby.ast.BeginNode.interpret(BeginNode.java:83)
    at org.jruby.ast.NewlineNode.interpret(NewlineNode.java:104)
    at org.jruby.ast.BlockNode.interpret(BlockNode.java:71)
    at org.jruby.ast.EnsureNode.interpret(EnsureNode.java:96)
    at org.jruby.internal.runtime.methods.InterpretedMethod.call(InterpretedMethod.java:201)
    at org.jruby.internal.runtime.methods.DefaultMethod.call(DefaultMethod.java:183)

set -XX:MaxHeapSize and -Xmx vm parameters