[jira] [Commented] (COLLECTIONS-429) Performance problem in MultiValueMap

["Thomas Neidhart (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/COLLECTIONS-429?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13560800#comment-13560800 ] 

Thomas Neidhart commented on COLLECTIONS-429:
---------------------------------------------

Hi Adrian,

thanks for your patch, the performance improvement is really significant.
I was trying to improve the code snippets and came up with a rather elegant solution reusing existing methods in CollectionUtils:

{noformat}
        @Override
        public boolean containsAll(Collection<?> c) {
             Collection<Object> result = CollectionUtils.<Object>intersection(this, c);
             return result.size() == c.size();
        }
{noformat}

This could also be added as a CollectionUtils.containsAll method, similar to the already existing containsAny.

The contract of containsAll should be fully supported by that snippet.
                
> Performance problem in MultiValueMap
> ------------------------------------
>
>                 Key: COLLECTIONS-429
>                 URL: https://issues.apache.org/jira/browse/COLLECTIONS-429
>             Project: Commons Collections
>          Issue Type: Bug
>    Affects Versions: 3.2.1
>         Environment: java 1.6.0_24
> Ubuntu 11.10
>            Reporter: Adrian Nistor
>         Attachments: patchFull_AbstractHashedMap.diff, patchFull.diff, patchFull_StaticBucketMap.diff, patchSmall_AbstractHashedMap.diff, patchSmall.diff, patchSmall_StaticBucketMap.diff, Test_AbstractHashedMap.java, TestDifferentParameter.java, Test.java, Test_StaticBucketMap.java
>
>
> Hi,
> 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:
> multi.values().containsAll(toContain);
> "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
> method.
> 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
> correct?
> Thanks,
> Adrian

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