You can try setting the JVM documents as per recommended setup instruction
It's important to use the latest JVM (Java Virtual Machine) for your platform as well as the correct GC (garbage collection) settings. Clearspace requires at least a 1.5 VM; 1.6 is recommended.
Heap Startup Parameters 1 GB -Xms512m -Xmx1024m -XX:MaxPermSize=256m -XX:+UseParNewGC -XX:+UseConcMarkSweepGC 2 GB -Xms512m -Xmx2048m -XX:MaxPermSize=256m -XX:+UseParNewGC -XX:+UseConcMarkSweepGC
In both cases this will allocate a 512 MB heap at minimum as well as allocate 256 MB to the "PermGen" space of the VM heap
You can find the detailed information here