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Date: Thu, 27 Apr 2006 19:58:37 +0000 (GMT+00:00)
From: "Christopher A. Larrieu (JIRA)" <jira@apache.org>
To: activemq-dev@geronimo.apache.org
Subject: [jira] Commented: (AMQ-688) Avoid blocking producers
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    [ 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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