Do you know that JVM (or JDK) with 32-bit is only able to use the maximum memory of 1.5GB? I just notice when I install a JVM (without check if it's a 32 bit installer file) on my server of 64-bit OS with the same bit of Tomcat installing, I couldn't extend the memory more than 1.5GB for the application. To check, 32bits or not So it's very important to use full capacity of 64-bit OS by using the same for the application architecture. Understanding of 32-bit & 64-bit, read this post .
Diary of Java Programming language