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From "Aidan Skinner (JIRA)" <qpid-...@incubator.apache.org>
Subject [jira] Commented: (QPID-942) Introduce client flow control and broker overflow protection
Date Mon, 23 Jun 2008 16:34:45 GMT

    [ https://issues.apache.org/jira/browse/QPID-942?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12607283#action_12607283
] 

Aidan Skinner commented on QPID-942:
------------------------------------

Proposed design at http://cwiki.apache.org/confluence/display/qpid/Producer+flow+control

> Introduce client flow control and broker overflow protection
> ------------------------------------------------------------
>
>                 Key: QPID-942
>                 URL: https://issues.apache.org/jira/browse/QPID-942
>             Project: Qpid
>          Issue Type: Bug
>          Components: Java Broker, Java Client
>    Affects Versions: M2.1
>            Reporter: Marnie McCormack
>            Assignee: Aidan Skinner
>             Fix For: M3
>
>
> Certainly the Java, and probably the other clients do not obey flow-control commands
from the broker. The Java broker never sends them to clients either. This is in the 0-8 spec.
so not fully AMQP compliant without it. 
> Client Work
> -------------------
> Flow control to be implemented in clients. The clients must also have buffer limiting
in place prior to this, or flow-controlling a client will only shift OOMEs from the broker
to the clients. Bounded buffers plus back-pressure from the broker will should ultimately
lead to the 'send' method blocking once the system as a whole is completely saturated. This
may mean that the broker gets a needed opportunity to chew its way through the back-log, resulting
in healthy throughputs under saturation. 
> Broker Work
> ------------------
> A strategy for deciding when to flow control clients from the broker needs to be decided
upon. Flow-control has per-connection granularity, which makes deciding when to do it on a
per route basis awkward. Flow-control may be triggered by: 
> 1. The broker being low on memory globally across the message store and all queues. 
> 2. A client attempting to publish to a queue that is beyond its max-depth. 
> 3. Based on history of destinations a client usually publishes to (or has published to),
flow-control client if one of them is beyond max-depth. 
> A well-conditioned application will not experience 'send' blocking, except under exceptional
loads, whereupon it will act as a safety valve to prevent either clients or broker from throwing
OOME. The other scenario that may cause back-logs, is slow consumers without TTL. 
> No time estimate for this yet, as its a fairly large piece of work, and not yet decided
exactly how its to be done. Need a design proposal before starting work, to be reviewed by
the qpid-dev group.

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