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From "Gary Tully (JIRA)" <>
Subject [jira] [Created] (AMQ-4485) Skipped message dispatch with concurrent transacted sends at cursor memory limit
Date Thu, 25 Apr 2013 12:32:16 GMT
Gary Tully created AMQ-4485:

             Summary: Skipped message dispatch with concurrent transacted sends at cursor
memory limit
                 Key: AMQ-4485
             Project: ActiveMQ
          Issue Type: Bug
          Components: Broker
    Affects Versions: 5.8.0
            Reporter: Gary Tully
            Assignee: Gary Tully
             Fix For: 5.9.0

With multiple concurrent transacted sends, transaction synchronisation after completions are
used to update the cursors.
These happen independent of the order that the store is updated, and hence the store order
When the cache is exhausted, a callback to the store to mark the end of caching assumes matching
order. If scheduling has swapped the order, it is possible to mark the order index past what
is cached and it is possible to skip a dispatch. Alternatively it is possible to mark too
early which results in duplicate dispatch if the audit is disabled or exhausted.

The senario that exposed this occurrence used concurrent transacted sends to 100 destinations
with slow consumers. Leaving scope for out of order processing and ensuring that the cache
is exhausted.

Using a large destination memory limit or systemUsage limit or useCache=false policy entry
will avoid this problem. The order is only important when the cache is exhausted.
In the skipped case, the message appears on the queue but is not consumable, however it is
consumable after a restart.

The proper fix is to ensure cursors are updated in the same order as the store.

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