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From "Branimir Lambov (JIRA)" <uima-...@incubator.apache.org>
Subject [jira] Updated: (UIMA-1364) Concurrent modification checks dominate index iteration time.
Date Tue, 02 Jun 2009 13:41:07 GMT

     [ https://issues.apache.org/jira/browse/UIMA-1364?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Branimir Lambov updated UIMA-1364:
----------------------------------

    Attachment: ConcurrentModificationPatch.txt

> Concurrent modification checks dominate index iteration time.
> -------------------------------------------------------------
>
>                 Key: UIMA-1364
>                 URL: https://issues.apache.org/jira/browse/UIMA-1364
>             Project: UIMA
>          Issue Type: Improvement
>            Reporter: Branimir Lambov
>         Attachments: ConcurrentModificationPatch.txt
>
>
> Iterating over the annotation index with even a moderate number of defined types is dominated
by the time spent checking individual indexes for concurrent modification. This is due to
the fact that concurrent modification checks are done on all types being iterated over, even
if the iteration only needs to process a couple of iterators. In fact, checking all iterators
for modification has linear complexity in the number of subiterators used, while the actual
iteration can be implemented with logarithmic complexity using e.g. a binary heap.
> The UIMA documentation and JavaDoc do not state that the iterators should always recognize
concurrent modification (FSIterator JavaDoc states "Implementations of this interface are
not required to be fail-fast. That is, if the iterator's collection is modified, the effects
on the iterator are in general undefined."). It thus makes sense to reduce the number of iterators
being tested for concurrent modification at each moveToNext() step.
> The attached patch replaces the checkConcurrentModificationAll() call in FSIndexRepositoryImpl.PointerIterator.moveToNext()
with concurrent modification checks on only the iterators being used by the step; as the iterator
becomes invalid it also checks all involved iterators for modification. By doing this it should
be able to catch almost all concurrent modification without the excessive overhead.
> In one of our performance tests iterating over the annotation index with 140 types defined
is more than twice faster after the attached patch is applied.

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