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From Rob Godfrey <rob.j.godf...@gmail.com>
Subject Re: Accumulation of Links from global shared durable subscriptions (JMS 2.0)
Date Fri, 03 Nov 2017 16:58:03 GMT
On 1 November 2017 at 10:16, Lorenz Quack <quack.lorenz@gmail.com> wrote:

> Hi,
>
> We noticed a potential problem with the way JMS 2.0 global shared
> durable subscriptions are implemented in the JMS client.  The
> implementation was designed, discussed, and implemented in QPIDJMS-220
> [1].
>
> When a consumer of a subscription closes the underlying AMQP link is
> not closed but merely detached since the closing of a subscription
> link is used as the signal to unsubscribe the subscription.  These
> subscription links remain on the broker until the subscription is
> unsubscribed (detach with close=true) at which point the broker
> discards all links associated with the subscription.
>
> For non-global subscriptions this does not seem to be a problem since
> the clientId is used as the container-id and links are reused if
> possible.
>
> For global subscription on the other hand the client uses a random
> UUID associated with the connection as its own container-id.  This
> means that on every new connection a new link is being estblished
> rather than recovering an existing one.  Over time these subscription
> links would accumulate on the broker until the subscription is
> unsubscribed.
>
> Since shared durable subscriptions are expected to be long lived this
> raises some concerns with regards to resource exhaustion on the
> broker.  An application that would spin up a connection do some work
> on a shared durable global subscription and then disconnect again
> would be "leaking" links.
>
> Due to this concern we plan on disabling shared durable global
> subscriptions for the initial v7 release of Qpid Broker-J.  There will
> be a context variable to enable the feature.
>
>
It seems to me a real shame that we are disabling this feature of JMS 2.0
because of the fact that from an AMQP point of view the link *may* be
resumed, but in practice, with JMS, will never be.  Would it not be better
to have a context variable which affects the behaviour of such links to
shared durable subscriptions such that if the context variable returns
"true" the links are removed from the link registry at the time of
connection closure, and if the context value is false, then the current
behaviour is maintained.  We could then later add functionality to the
client to specify (via some flag) the behaviour it desires (thus ultimately
removing the need for the context variable)?

-- Rob


>
> Thoughts, comments, discuss!
>
> Kind regards,
> Lorenz
>
>
> [1] https://issues.apache.org/jira/browse/QPIDJMS-220
>
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