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From "Stirling Chow (JIRA)" <>
Subject [jira] [Created] (AMQ-3312) Queue's moveMatchingMessagesTo method is extremely slow to the point of being unusuable as Queue size increases
Date Mon, 09 May 2011 23:51:03 GMT
Queue's moveMatchingMessagesTo method is extremely slow to the point of being unusuable as
Queue size increases

                 Key: AMQ-3312
             Project: ActiveMQ
          Issue Type: Bug
          Components: Broker
    Affects Versions: 5.5.0
            Reporter: Stirling Chow

We have a system based on ActiveMQ that stores messages in a non-peristent queue.  Frequently,
we have to move a specific message from this queue to another queue.  The message to be moved
may be anywhere in the queue, and is identified by a selector on a custom JMS integer property.

To facilitate the selection and move, we use
context, String selector, ActiveMQDestination dest)

We've found that once our queue grows past 10K messages, moving a single message takes over
10s.  When the queue grows past 20K messages, a move takes 70s.  It's clear from testing that
the time to move a message grows exponentially as the queue size increases, to the point that
moveMatchingMessagesTo becomes unusable.

AMQ 5.5.0 has this implementation for moveMatchingMessagesTo:

{code:title=Queue#moveMatchingMessagesTo(ConnectionContext context, MessageReferenceFilter
    public int moveMatchingMessagesTo(ConnectionContext context, MessageReferenceFilter filter,
            ActiveMQDestination dest, int maximumMessages) throws Exception {
        int movedCounter = 0;
        Set<QueueMessageReference> set = new CopyOnWriteArraySet<QueueMessageReference>();
        do {
            }finally {
            List<QueueMessageReference> list = new ArrayList<QueueMessageReference>(set);
            for (QueueMessageReference ref : list) {
                if (filter.evaluate(context, ref)) {
                    // We should only move messages that can be locked.
                    moveMessageTo(context, ref, dest);
                    if (++movedCounter >= maximumMessages && maximumMessages >
0) {
                        return movedCounter;
        } while (set.size() < this.destinationStatistics.getMessages().getCount() &&
set.size() < maximumMessages);
        return movedCounter;

In the context that we use, maximumMessages is Integer.MAXINT:

{code:title=moveMatchingMessagesTo(ConnectionContext context, String selector, ActiveMQDestination
    public int moveMatchingMessagesTo(ConnectionContext context, String selector, ActiveMQDestination
            throws Exception {
        return moveMatchingMessagesTo(context, selector, dest, Integer.MAX_VALUE);

Since moveMatchingMessagesTo instantiates the set variable as a CopyOnWriteArraySet, each
doPageIn loop creates a new array, copies the existing set members, and then linearly scans
the array for the insertion.  The result is that moveMatchingMessagesTo is an O(n^2) algorithm
with respect to message copying, where n is the size of the queue.

set is scoped to a single call of moveMatchingMessagesTo, and is only accessed by a single
thread, so there is no benefit to using CopyOnWriteArraySet.  Simply changing set to a HashSet
prevents the need for the doPageIn loop to copy the set on each iteration, and insertion becomes
an O(1) operation.

Attached is a unit test that demonstrates how moving the last message from a queue of 10K
messages takes 8s (on our machine).  Included is a patch Queue that changes set from a CopyOnWriteArraySet
to a HashSet; with this patch, the same unit test completes in under 200ms.

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