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https://issues.apache.org/jira/browse/QPID-3157?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Keith Wall resolved QPID-3157.
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Resolution: Fixed
Reviewed, no comments.
> 'removed' subscriptions may be held in memory by the queues SubscriptionList
> or 'lastSubscriptionNode' reference
> ----------------------------------------------------------------------------------------------------------------
>
> Key: QPID-3157
> URL: https://issues.apache.org/jira/browse/QPID-3157
> Project: Qpid
> Issue Type: Bug
> Components: Java Broker
> Affects Versions: 0.5, 0.6, 0.7, 0.8, 0.9, 0.10, 0.11, 0.12
> Reporter: Robbie Gemmell
> Assignee: Keith Wall
> Priority: Critical
> Fix For: 0.13
>
>
> subscriptions 'removed' from a queue subscription list are only marked
> deleted and can not actually bereleased from memory until the head of the
> subscription list advances beyond them. Additionally and perhaps more
> troublesome, a queues 'lastSubscriptionNode' can refer to a particular
> subscription but hold *all* subscequent subscriptions in memory whether they
> have been deleted or not and regardless whether the head of the
> SubscriptionList has advanced beyond them,
> As a result any memory in use by the now-closed subscription will not be
> released until the queue is deleted, or all the subscriptions prior to it are
> closed and removed from the list *and* the 'lastSubscriptionNode' advances
> beyond them.. This also holds the associated ServerSession in memory, which
> is currently a rather heavyweight object.
> This issue is further compounded when the queue has a backlog of messages and
> consumers are then created, used to recieve one message, and closed. In this
> scenario the broker sends the client as many messages as it can prefetch,
> leading to creation of up to <prefetch size, default=500> MessageTransfer
> commands, all which are recorded in the ServerSession but then left retained
> as 'unprocessed' in the closed session, which might be held in memory as
> described above. This results in an explosion in the number of
> MessageTransfer commands retained in memory as each message can have up to
> <prefetch size> MessageTransfer commands associated with it before it is
> eventually consumed by a client and all of thse will also be retained in
> memory by a 'removed' but not deleted subscription. The last effect can be
> combated by restricting the preftech size (eg appending &maxprefetch='1' to
> the connection url).
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