Performance ConcurrentHashmap vs HashMap

by

I was really surprised to find this topic to be so old and yet no one has yet provided any tests regarding the case. Using ScalaMeter I have created tests of add, get and remove for both HashMap and ConcurrentHashMap in two scenarios:

  1. using single thread
  2. using as many threads as I have cores available. Note that because HashMap is not thread-safe, I simply created separate HashMap for each thread, but used one, shared ConcurrentHashMap.

Code is available on my repo.

The results are as follows:

  • X axis (size) presents number of elements written to the map(s)
  • Y axis (value) presents time in milliseconds

Add method
Get method
Remove method

The summary

  • If you want to operate on your data as fast as possible, use all the threads available. That seems obvious, each thread has 1/nth of the full work to do.

  • If you choose a single thread access use HashMap, it is simply faster. For add method it is even as much as 3x more efficient. Only get is faster on ConcurrentHashMap, but not much.

  • When operating on ConcurrentHashMap with many threads it is similarly effective to operating on separate HashMaps for each thread. So there is no need to partition your data in different structures.

To sum up, the performance for ConcurrentHashMap is worse when you use with single thread, but adding more threads to do the work will definitely speed-up the process.

Testing platform

AMD FX6100, 16GB Ram
Xubuntu 16.04, Oracle JDK 8 update 91, Scala 2.11.8

More Related Contents:

  1. What are the differences between a HashMap and a Hashtable in Java?
  2. Which Java Collection should I use?
  3. Why there is no ConcurrentHashSet against ConcurrentHashMap
  4. Best way to create a hashmap of arraylist
  5. Java: how to convert HashMap to array
  6. get string value from HashMap depending on key name
  7. Is there a way to get the value of a HashMap randomly in Java?
  8. Difference between HashSet and HashMap?
  9. Shortcut for adding to List in a HashMap
  10. How does ConcurrentHashMap work internally?
  11. Comparing two hashmaps for equal values and same key sets?
  12. what is the method to delete hashmap entry
  13. How to check if an integer is in a set of given ranges? [closed]
  14. Java 8 Streams hashmap
  15. Java Compare Two Lists
  16. java.lang.OutOfMemoryError: GC overhead limit exceeded [duplicate]
  17. How do I convert a Map to List in Java?
  18. Define a fixed-size list in Java
  19. What is the difference between an ordered and a sorted collection?
  20. Java – How to create new Entry (key, value)
  21. Why does Collections.sort use Mergesort but Arrays.sort does not?
  22. How to modify a Collection while iterating using for-each loop without ConcurrentModificationException? [duplicate]
  23. ArrayList as key in HashMap
  24. Any implementation of Ordered Set in Java?
  25. Java HashMap – deep copy
  26. JDK9 randomization on immutable sets and maps
  27. In what situations is the CopyOnWriteArrayList suitable? [duplicate]
  28. Hashmap implementation to count the occurrences of each character
  29. Perform operation on n random distinct elements from Collection using Streams API
  30. Explanation of HashMap#hash(int) method

Leave a Comment