String Deduplication feature of Java 8

by

@assylias answer basiclly tells you how it work and is very good answer. I have tested a production application with String Deduplication and have some results. The web app heavily uses Strings so i think the advantage is pretty clear.

To enable String Deduplication you have to add these JVM params (you need at least Java 8u20):

-XX:+UseG1GC -XX:+UseStringDeduplication -XX:+PrintStringDeduplicationStatistics

The last one is optional but like the name says it shows you the String Deduplication statistics. Here are mine:

[GC concurrent-string-deduplication, 2893.3K->2672.0B(2890.7K), avg 97.3%, 0.0175148 secs]
   [Last Exec: 0.0175148 secs, Idle: 3.2029081 secs, Blocked: 0/0.0000000 secs]
      [Inspected:           96613]
         [Skipped:              0(  0.0%)]
         [Hashed:           96598(100.0%)]
         [Known:                2(  0.0%)]
         [New:              96611(100.0%)   2893.3K]
      [Deduplicated:        96536( 99.9%)   2890.7K( 99.9%)]
         [Young:                0(  0.0%)      0.0B(  0.0%)]
         [Old:              96536(100.0%)   2890.7K(100.0%)]
   [Total Exec: 452/7.6109490 secs, Idle: 452/776.3032184 secs, Blocked: 11/0.0258406 secs]
      [Inspected:        27108398]
         [Skipped:              0(  0.0%)]
         [Hashed:        26828486( 99.0%)]
         [Known:            19025(  0.1%)]
         [New:           27089373( 99.9%)    823.9M]
      [Deduplicated:     26853964( 99.1%)    801.6M( 97.3%)]
         [Young:             4732(  0.0%)    171.3K(  0.0%)]
         [Old:           26849232(100.0%)    801.4M(100.0%)]
   [Table]
      [Memory Usage: 2834.7K]
      [Size: 65536, Min: 1024, Max: 16777216]
      [Entries: 98687, Load: 150.6%, Cached: 415, Added: 252375, Removed: 153688]
      [Resize Count: 6, Shrink Threshold: 43690(66.7%), Grow Threshold: 131072(200.0%)]
      [Rehash Count: 0, Rehash Threshold: 120, Hash Seed: 0x0]
      [Age Threshold: 3]
   [Queue]
      [Dropped: 0]

These are the results after running the app for 10 minutes. As you can see String Deduplication was executed 452 times and “deduplicated” 801.6 MB Strings. String Deduplication inspected 27 000 000 Strings. When i compared my memory consumption from Java 7 with the standard Parallel GC to Java 8u20 with the G1 GC and enabled String Deduplication the heap dropped approximatley 50%:

Java 7 Parallel GC

Java 7 Parallel GC

Java 8 G1 GC with String Deduplication

Java 8 G1 GC with String Deduplication

More Related Contents:

  1. Why is String.chars() a stream of ints in Java 8?
  2. Why StringJoiner when we already have StringBuilder?
  3. incompatible types required char found java.lang.string
  4. All possible Angram String combinations in java [closed]
  5. How to convert Java String into byte[]?
  6. Explicitly calling a default method in Java
  7. Swing rendering appears broken in JDK 1.8, correct in JDK 1.7
  8. ArrayList initial capacity and IndexOutOfBoundsException [duplicate]
  9. CharSequence VS String in Java?
  10. Java 8 lambdas group list into map
  11. How does Java 8′ new default interface model works (incl. diamond, multiple inheritance, and precedence)?
  12. Converting String to “Character” array in Java
  13. What is the difference between Optional.flatMap and Optional.map?
  14. Convert String to Uri
  15. Java8 Lambdas and Exceptions
  16. Why can’t I get a duration in minutes or hours in java.time?
  17. Why can method reference use non-final variables?
  18. stream on JPA lazy list
  19. Calculating frequency of each word in a sentence in java
  20. Remove all non-“word characters” from a String in Java, leaving accented characters?
  21. Does Java 8 provide a good way to repeat a value or function?
  22. Fastest way to strip all non-printable characters from a Java String
  23. Simple way to sort strings in the (case sensitive) alphabetical order
  24. How to short-circuit a reduce() operation on a Stream?
  25. Want to create a stream of characters from char array in java
  26. DateTimeFormatter Support for Single Digit Day of Month and Month of Year
  27. Erratic performance of Arrays.stream().map().sum()
  28. Old JaxB and JDK8 Metaspace OutOfMemory Issue
  29. split string only on first instance – java
  30. Java 8 Supplier Exception handling with CompletableFuture

Leave a Comment