[jira] [Created] (QPID-6528) Multiple starving suspended consumers on a single session might hold the reference to old deleted queue entry via QueueContext#_lastSeenEntry causing accumulation of deleted queue entries in Broker memory which can eventually lead to OOM

["Alex Rudyy (JIRA)" <ji...@apache.org>]

Alex Rudyy created QPID-6528:
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             Summary: Multiple starving suspended consumers on a single session might hold the reference to old deleted queue entry via QueueContext#_lastSeenEntry causing accumulation of deleted queue entries in Broker memory which can eventually lead to OOM
                 Key: QPID-6528
                 URL: https://issues.apache.org/jira/browse/QPID-6528
             Project: Qpid
          Issue Type: Improvement
          Components: Java Broker
    Affects Versions: 0.32, 0.30, 0.28, 0.26, 0.24, 0.22
            Reporter: Alex Rudyy


Broker might run into OOM due to holding a reference to an old deleted QueueEntry in QueueContext#_lastSeenEntry. The issue can occur with multiple consumers on a single session with a relatively ow prefetch. 

When session prefetch buffer becomes full, the flow is suspended, and subscription states are set to SUSPENDED. The delivery methods on AbstractQueue check whether subscription is not suspended(attempDelivery, consumerReadyAndJasInterest, processQueue, flushConsumer) before performing any delivery activity including _lastSeen update. Thus, message delivery does not happen for suspended subscriptions and _lastSeen field in Subscription context is not updated. Having many starving consumers on single session might cause accumulation of deleted queue entries and OOM




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