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  1. Commons Collections

Performance problem in MultiValueMap



    • Improvement
    • Status: Closed
    • Major
    • Resolution: Fixed
    • 3.2.1
    • 4.0-alpha1, 4.0
    • None
    • None
    • java 1.6.0_24
      Ubuntu 11.10



      I am encountering a performance problem in MultiValueMap. It appears
      in version 3.2.1 and also in revision 1366088. I attached a test that
      exposes this problem and a patch that fixes it. On my machine, for
      this test, the patch provides a 1158X speedup.

      To run the test, just do:

      $ java Test

      The output for the un-patched version is:
      Time is 44040

      The output for the patched version is:
      Time is 38

      The attached test shows that, for a "MultiValueMap multi" object, the
      following operation is very slow:


      "MultiValueMap.values()" returns a "MultiValueMap.Values" object,
      which inherits containsAll() from "java.util.AbstractCollection",
      which has quadratic complexity.

      I attached two patches. Both patches override containsAll() and
      implement a linear time algorithm. patchSmall.diff populates a
      HashSet eagerly, and patchFull.diff populates a HashSet lazily.
      patchFull.diff is faster than patchSmall.diff when containsAll()
      returns false after inspecting only a few elements, though in most
      cases they are equally fast. I am including patchSmall.diff just in
      case you prefer smaller code.

      Note that this problem is different from COLLECTIONS-416. As
      established in the COLLECTIONS-416 discussion, there the user was
      responsible for using the proper data structures as argument for the

      For "MultiValueMap.values()", the problem is not related to the
      collection passed as parameter. The problem will always manifest for
      this method, irrespective of the parameter type. I attached a test
      (TestDifferentParameter.java) that shows that, even with a HashSet
      parameter, the current problem still manifests (which did not happen
      for COLLECTIONS-416).

      This problem also exists for the two other "Values" classes
      (AbstractHashedMap.Values, StaticBucketMap.Values). I attached tests
      and patches for these classes as well. If you want me to file
      separate reports, just let me know.

      Is this truly a performance problem, or am I misunderstanding the
      intended behavior? If so, can you please confirm that the patches are




        1. TestDifferentParameter.java
          0.8 kB
          Adrian Nistor
        2. Test.java
          0.8 kB
          Adrian Nistor
        3. Test_StaticBucketMap.java
          0.8 kB
          Adrian Nistor
        4. Test_AbstractHashedMap.java
          0.8 kB
          Adrian Nistor
        5. patchSmall.diff
          0.8 kB
          Adrian Nistor
        6. patchSmall_StaticBucketMap.diff
          0.8 kB
          Adrian Nistor
        7. patchSmall_AbstractHashedMap.diff
          0.9 kB
          Adrian Nistor
        8. patchFull.diff
          1 kB
          Adrian Nistor
        9. patchFull_StaticBucketMap.diff
          1 kB
          Adrian Nistor
        10. patchFull_AbstractHashedMap.diff
          1 kB
          Adrian Nistor

        Issue Links



              Unassigned Unassigned
              adriannistor Adrian Nistor
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