[ https://issues.apache.org/activemq/browse/AMQ-688?page=comments#action_36103 ]
Christopher A. Larrieu commented on AMQ-688:
--------------------------------------------
How can we collaborate on this work? The described functionality is crucial to ActiveMQ's
success within our organization.
> Avoid blocking producers
> ------------------------
>
> Key: AMQ-688
> URL: https://issues.apache.org/activemq/browse/AMQ-688
> Project: ActiveMQ
> Type: New Feature
> Components: Broker
> Versions: 4.0 RC 2
> Reporter: Christopher A. Larrieu
> Assignee: Christopher A. Larrieu
> Fix For: incubation
>
> Original Estimate: 8 weeks
> Remaining: 8 weeks
>
> Our main goal
> is to avoid stalled producers by addressing the main culprit: too many undispatched messages
> in the broker's memory. Our motivation is to handle significant --though temporary--
imbalances
> between production and consumption rates.
> Reaching this goal entails specific broker modifications:
> 1. When memory gets tight, start dropping undispatched non-persistent messages. This
is the
> first-cut attempt to maintain throughput of persistent messages.
> Unlike the approach documented at http://docs.codehaus.org/display/ACTIVEMQ/Slow+Consumer+Handling,
> the message dropping will only occur after the UsageManager reaches capacity. Non-persistent
> messages in dispatch lists will be dropped according to per-destination policy. Subscriptions
> can purge their own messages triggered via callback from the UsageManager.
> 2. Evict messages if memory remains tight, to be fetched from backing store prior to
dispatch.
> ActiveMQ already supports this for persistent messages on Topics with durable subscriptions.
> If a consumer's prefetch buffer is full, the splash-over messages remain as IndirectMessageReference
> objects in the dispatch list, with the actual message body loaded from store on demand.
I
> believe we can extend this approach for Queues as well.
> 3. Improve the efficiency with which evicted messages are loaded back into memory.
> Currently, they are loaded one at a time as needed. It would make sense to batch-load
message
> sets periodically. This will require a significant shift in responsibilities between
objects,
> since an IndirectMessageReference doesn't know about other instances that can be loaded
in
> mass.
>
> The goal will be to keep each subscription dispatch list stocked with a decent number
of messages
> in-memory to reasonably trade-off between it's consumer's performance and resource usage
in
> the broker. As with everything else, we can implement this as a strategy class with
the first
> cut implementing a simple resource allocation strategy: divvy up available memory amongst
> all subscriptions and keep that memory filled with messages for dispatch. I envision
a worker
> task assuming responsibility for keeping these lists filled.
> 4. Even with the above modifications, we still can't entirely avoid blocked producers,
so
> we'd like to add client-configurable time-outs to provide a bound for the time a producer
> can remain stalled.
> Maybe this should be a new attribute of ActiveMQConnection: maxProducerFlowControlWait.
Calls
> to UsageManager.waitForSpace can take this quantity as an argument. Failure to reach
sufficient
> space for the new message will throw an exception back up the stack and across the wire,
letting
> the producer know that the message was not delivered.
> 5. Finally, we need to extend disk support for Topics that have only non-durable subscribers,
> otherwise their dispatch lists can fill up with persistent messages. In order to maintain
> compliance with JMS, it would be nice to provide some alternative to dropping persistent
messages.
> One possible first cut is to layer this on top of a DurableTopicSubscription by creating
an
> anonymous subscriber for every Topic that has only non-durable subscriptions. When all
such
> subscriptions terminate, the broker can remove the anonymous subscriber.
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