Java GC tuning for strings

Question

Profiling the application I figured out that there are a lot of strings on heap.

In my situation, strings are created on heap and not interned and they are not literals

Answer 1

Java 8 comes with a new GC feature -XX:+UseStringDeduplication.

After enabling this, GC would compare strings to find those with same char array value. Let's say str1 & str2 have the same char[], then GC would make str1 point to char[] of str2. This way char[] of str1 can be garbage collected and reclaim the memory. And since Strings are immutable, there is no risk of making multiple strings point to the same char[]

Answer 2

Related to -XX:+UseCompressedStrings, you should have a look at this question: Support for Compressed Strings being Dropped in HotSpot JVM?

And, related to -XX+UseStringCache, have a look at : JVM -XX:+StringCache argument?

Btw. Java 7 comes with nice features that allow tuning of String cache when using the interned Strings. See -XX:+PrintSTringTableStatistics and -XX:StringTableSize=n. This way you can optimize the String cache size.