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https://issues.apache.org/jira/browse/STORM-886?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14950027#comment-14950027
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ASF GitHub Bot commented on STORM-886:
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Github user rsltrifork commented on the pull request:
https://github.com/apache/storm/pull/700#issuecomment-146779690
Thanks for the quick reply, revans2.
> How do you know that the bolt is waiting in a controlled manner?
A Bolt sending to an external system can include a circuit breaker, so it
can keep waiting while the CB is tripped, while regularly retrying sends to
check if the recipient is up.
While doing this, the Bolt could also tell Storm that processing of the
current tuple is currently blocked, and that Storm should reset the tuple
timeout for it (and subsequent inflight tuples):
`collector.resetTupleTimeout(tuple);`
> Even if you do know that how do you know that if it is waiting in a
controlled manner that it has not lost track of a tuple?
The bolt is continuously saying that it still has the tuple.
> Automatic Back Pressure
> -----------------------
>
> Key: STORM-886
> URL: https://issues.apache.org/jira/browse/STORM-886
> Project: Apache Storm
> Issue Type: Improvement
> Components: storm-core
> Reporter: Robert Joseph Evans
> Assignee: Zhuo Liu
> Fix For: 0.11.0
>
> Attachments: aSimpleExampleOfBackpressure.png, backpressure.png
>
>
> This new feature is aimed for automatic flow control through the topology DAG
> since different components may have unmatched tuple processing speed.
> Currently, the tuples may get dropped if the downstream components can not
> process as quickly, thereby causing a waste of network bandwidth and
> processing capability. In addition, it is difficult to tune the
> max.spout.pending parameter for best backpressure performance. Therefore, an
> automatic back pressure scheme is highly desirable.
> Heron proposed a form of back pressure that does not rely on acking or max
> spout pending. Instead spouts throttle not only when max.spout.pending is
> hit, but also if any bolt has gone over a high water mark in their input
> queue, and has not yet gone below a low water mark again. There is a lot of
> room for potential improvement here around control theory and having spouts
> only respond to downstream bolts backing up, but a simple bang-bang
> controller like this is a great start.
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