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From "Adrian Nistor (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (COLLECTIONS-409) ListOrderedSet.addAll() is very slow
Date Tue, 19 Jun 2012 16:01:42 GMT

     [ https://issues.apache.org/jira/browse/COLLECTIONS-409?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Adrian Nistor updated COLLECTIONS-409:
--------------------------------------

    Attachment: Test.java
                patch.diff
    
> ListOrderedSet.addAll() is very slow
> ------------------------------------
>
>                 Key: COLLECTIONS-409
>                 URL: https://issues.apache.org/jira/browse/COLLECTIONS-409
>             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, patch.diff
>
>
> Hi,
> I am encountering a performance problem in ListOrderedSet.addAll().
> It appears in version 3.2.1 and also in revision 1351465 (18 Jun
> 2012). I have attached a test that exposes this problem and a
> three-line patch that fixes it. On my machine, for this test, the
> patch provides a 79X speedup.
> To run the test, just do:
> $ java Test
> The output for the un-patched version is:
> Time is 1837
> The output for the patched version is:
> Time is 23
> As the patch shows, the problem is that 
> ListOrderedSet.addAll(int index, Collection<? extends E> coll) 
> performs:
> "setOrder.add(index++, e)" for each element in "coll".  This is very 
> expensive, because "setOrder" is an ArrayList, and inserting an
> element in the middle of an ArrayList shifts all the elements to the
> right.
> The patched version avoids this cost by inserting all the elements at
> once, thus performing only one insert.
> Is this a bug?  If so, can you please confirm that the patch is
> correct?
> Thanks,
> Adrian

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