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https://issues.apache.org/jira/browse/PROTON-2790?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17879580#comment-17879580
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ASF GitHub Bot commented on PROTON-2790:
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cliffjansen opened a new pull request, #434:
URL: https://github.com/apache/qpid-proton/pull/434
This patch provides an implementation of PROTON-2790 to provide finer
grained management of session based flow control over input buffering.
In addition to limiting the absolute size of the inbound buffered data, this
patch allows the application to choose how soon the peer is notified of new
available space (the existing method waits until the capacity is fully used up
which can result in needless transmission stalls). This is particularly useful
for large messages or streaming messages which are broken into multiple AMQP
transfer frames.
The patch also allows the sending peer the ability to query what is the most
recently communicated window size (pn_session_remote_incoming_window).
This patch also prevents anti-patterns that are possible in the current
session flow model that can lead to PN_TRANSPORT_ERROR termination of the
connection. Namely the transport maximum frame size and the session incoming
window will not be allowed to change at arbitrary times (which can otherwise
allow the incoming window to become negative). Session "capacity" can still be
changed at any time to preserve existing usage for applications that may rely
on this API (now deprecated).
This patch strives to send the least number of additional AMQP frames on the
wire to achieve the intended result. No extra frames are sent if link credit
flow frames are already pending on the session or if the incoming window is
currently at or above the low water mark.
The existing session flow model based on byte capacity is marked as
deprecated in favor of this alternative flow control model. The code is
structured to allow the easy removal of the "capacity" model in future.
> Improve session flow control
> ----------------------------
>
> Key: PROTON-2790
> URL: https://issues.apache.org/jira/browse/PROTON-2790
> Project: Qpid Proton
> Issue Type: Improvement
> Components: proton-c
> Affects Versions: proton-c-0.39.0
> Reporter: Clifford Jansen
> Assignee: Clifford Jansen
> Priority: Major
>
> Current flow control replenishment for the session incoming window only
> occurs when the window reaches 0. This minimizes flow frames on the wire but
> introduces a stall in transfer processing.
> Switching to using a low watermark for the session incoming window would
> allow the application to choose a preferred trade off between transfer stalls
> and FLOW frames.
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