String Deduplication - New Java 8 update 20 feature

Duplicate Strings in JVM heap ..Worried ??


During JVM heap dump parsing, it is quite common to visualize that Strings are consuming lots of heap space. Especially char[] are always ( most of the cases) present as biggest object in histogram.

If we perform a deeper analysis on String objects it is quite common to encounter thousands of duplicate String instances. Controlling these duplicate Strings may provide improvement in overall JVM memory footprints.

With Java 8 update 20 we now have a new features called String Deduplication which require G1 garbage collector in place and this feature is turned off by default.

Here G1 GC identifies Strings which are duplicated more than once and correct them to point to same internal char[], to avoid multiple copies of the same string.

Parameter :  -XX:+UseStringDeduplication