Reference: http://www.programgo.com/article/2423569571/
A server stuck and the derived java_opts
JAVA_OPTS="$JAVA_OPTS -Xmn768m -Xms2048m -Xmx2048m -XX:PermSize=128m -XX:MaxPermSize=256m"
See http://stackoverflow.com/questions/2915276/what-is-the-default-maximum-heap-size-for-suns-jvm-from-java-se-6 , the maximum can be eaten without setting mx to 1/4 of physical memory
For some information about JAVA_OPTS, you can refer to the java official website documentation. Many documents found will talk about how to set mn, ms, mx, etc. The default value can only be found from official documents. For example, what happens if I don't set it, such as http://www.oracle.com/technetwork/java/ javase/6u18-142093.html , ms, initial heap size, if not set, minimum 8M, generally 1/64 of physical memory