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https://issues.apache.org/jira/browse/QPID-6255?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14241136#comment-14241136
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Ken Giusti commented on QPID-6255:
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I think I can account for the performance difference:
I did a callgrind analysis of the two different approaches (polled vs. event)
and the 'instruction cost' of the event implementation is a little more than an
order of magnitude higher (0.35% vs 0.02% as a percentage of the total
instruction count).
Digging a little further it turns out that the event handler is actually
discarding about 50% of the received events. About 1/4 of the total events are
PN_TRANSPORT events, which the driver ignores (pending output is checked later
in the code). The really interesting bit is that there is a PN_LINK_FLOW for
_every_ transmitted frame! The actual on-the-wire flow frames are much less
(like 100x less).
The engine emits a PN_LINK_FLOW from two points in the code: when a flow frame
arrives, and when credit is consumed (a transfer is done). IMHO, these are two
semantically different events. I would argue that they should be treated as
such.
I've hacked a local copy of proton to stop emitting PN_LINK_FLOW events on
credit consumption, and PN_TRANSPORT events entirely and the resulting
performance improvements bring it to parity with the polled approach.
I think if Proton allowed event filtering (so we could avoid the PN_TRANSPORT
events) and split the flow events into two separate events we could improve
this patch. I'll raise this on the mailing list.
> [amqp1.0] Migrate to the new Proton event API
> ---------------------------------------------
>
> Key: QPID-6255
> URL: https://issues.apache.org/jira/browse/QPID-6255
> Project: Qpid
> Issue Type: Improvement
> Components: C++ Broker
> Affects Versions: 0.30
> Reporter: Ken Giusti
> Assignee: Ken Giusti
> Fix For: Future
>
>
> Proton version 0.8 introduced an event-based API. The Qpid broker currently
> uses the older API which requires a linear search of deliveries, links, and
> sessions during event processing. Migrating to the new API _should_ optimize
> event processing, especially as the number of object instances scale.
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