The 64 bit JDK can allocate more memory (> 2GB) to java applications, but 32 bit JDK is usually 0%-10% faster. SparkGateway doesn't use too much memory, so you can install 32bit JDK and keep an eye on the memory usage. Also make sure you are using JDK instead of JRE if you are using 32bit Java, because 32 bit JRE doesn't include the server side JIT.