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https://issues.apache.org/jira/browse/AMQ-6239?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15235073#comment-15235073
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Christopher L. Shannon commented on AMQ-6239:
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I'm not sure if thread safety is a big issue here without looking deeper into
it. I believe every place the pending lists are used either have new lists
allocated for that thread, or there is synchronization done at a higher level,
such as the FilePendingMessageCursor which uses synchronized on adds and
removes.
> 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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