Adrian Nistor created COLLECTIONS-429: -----------------------------------------
Summary: 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: Test.java, TestDifferentParameter.java, Test_AbstractHashedMap.java, Test_StaticBucketMap.java, patchFull.diff, patchFull_AbstractHashedMap.diff, patchFull_StaticBucketMap.diff, patchSmall.diff, patchSmall_AbstractHashedMap.diff, patchSmall_StaticBucketMap.diff 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 -- This message is automatically generated by JIRA. If you think it was sent incorrectly, please contact your JIRA administrators: https://issues.apache.org/jira/secure/ContactAdministrators!default.jspa For more information on JIRA, see: http://www.atlassian.com/software/jira