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javaperformancejvmjvm-hotspot

What is current status of Oracle Java HotSpot VM performance options (+UseStringCache, +UseCompressedStrings, +OptimizeStringConcat)

I was reading Java HotSpot VM Options. I've seen some interesting VM switches, mostly pertaining to Strings - which is of great value to me since my app is doing some heavy String manipulation. Those are:

  • -XX:+UseStringCache
  • -XX:+UseCompressedStrings
  • -XX:+OptimizeStringConcat

I was wondering - are these switches on by default? What is real world experience in using them? Do they make a difference?

Solution

  • Considering String performance, have a look at the -XX:+PrintStringTableStatistics and -XX:StringTableSize=. Java 7 comes with nice features that allow tuning of String cache when using the interned Strings. This way you can optimize the String cache size.

    And, a related String Performance Q/A: Java GC tuning for strings