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https://issues.apache.org/jira/browse/AMQ-6239?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15235106#comment-15235106
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Timothy Bish commented on AMQ-6239:
-----------------------------------
As a point of reference the previous algorithm wasn't thread safe either, as
concurrent calls to next could return the same node value under the right
circumstances, so you could make some reasonable assumptions that the usage is
done within proper locks.
> Performance issue in PrioritizedPendingListIterator
> ---------------------------------------------------
>
> Key: AMQ-6239
> URL: https://issues.apache.org/jira/browse/AMQ-6239
> Project: ActiveMQ
> Issue Type: Improvement
> Components: Broker
> Affects Versions: 5.12.2
> Reporter: Martin Lichtin
> Attachments: AMQ-6239-yourkit-1.jpg, PrioritizedPendingList.java.patch
>
>
> Sending and consuming 5000 messages to/from a queue, one can see heavy CPU
> use on the broker side (v 5.12.2).
> Yourkit shows
> PrioritizedPendingList$PrioritizedPendingListIterator.<init>
> as a hot spot method. It calls ArrayList.add(Object) around 12 mio times.
> Situation is that FilePendingMessageCursor.isEmpty() iterates over in-memory
> messages and therefore (as it is a prioritized queue) uses
> PrioritizedPendingListIterator which uses OrderedPendingList.getAsList()
> which overall turns out to be an expensive method as it converts the
> self-managed linked list to a Java ArrayList and then this list is filled
> into another ArrayList managed by PrioritizedPendingListIterator.
> PrioritizedPendingListIterator could be improved to walk the priority lists
> via OrderedPendingList iterators, as these are implemented efficiently.
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