By asantaga on Nov 29, 2011
Just received an email from one of our JVM developers who read my blog entry on Performance tuning JDeveloper11g and he's confirmed that all of the above parameters are totally supported :-) He's also provided a description of the parameters so we can learn what magic is actually being applied.
- -XX:+AggressiveOpts -- this enables the latest and greatest JVM optimizations. It will likely help most Java applications. It's fully supported. The downside of it is that because it has the latest and greatest optimizations, there is some small probability that it may not offer as good of an experience. As those features enabled with this command line option have "matured", they are made the default in a future JDK release. So, you can think of this command line option as the place where the newest optimizations get introduced. Some time later they are moved out from under AggressiveOpts to become default behavior.
-- only works with the -server JVM. It may be enabled by the default in a future JDK 7 update release. This option delays the construction of a StringBuilder/StringBuffer and attempts to avoid re-sizing the underlying char by attempting to detect the size of the char to allocate based on what's being appended to the StringBuilder/StringBuffer.
-- I would not suggest using this unless you knew that JDeveloper allocated the same string over and over again. And, the string that's allocated over and over again is one of the first 100,000 allocated strings. In short, I'd recommend against using it. And, in fact, in Java 7 (currently) does not include this feature.
-- applicable to 64-bit JVMs. And, if you're using a 64-bit JVM, I'd suggest you use it. It's auto enabled in JDK 7 64-bit JVMs and later JDK 6 64-bit JVMs enable it by default too.
-- by default this option is already enabled.
One other command line option to consider is -XX:+TieredCompilation for a JDK 6 Update 25 or later, or JDK 7. This gives you the startup of a -client JVM and the peak performance of a -server JVM.