Github user miguno commented on the pull request:
https://github.com/apache/storm/pull/429#issuecomment-74050954
Thanks for your feedback, Nathan.
As far as I understand this patch does not enable backpressure. But:
because there is no backpressure (yet) that we can rely on, this patch will
improve at least the situation during the startup phase of a topology to
prevent that a) an unacked topo will not lose messages during the startup, and
b) we do not need to unnecessarily replay messages in case of acked topos
during their startup. This is achieved by checking that all worker connections
are ready before the topology starts processing data.
So backpressure is still an open feature. Backpressure was IIRC mentioned
in the initial PR because there was a deficiency (dating back to a ZMQ related
TODO) that caused problems related to this PR/Storm tickets (327, 404, and one
more). However, this patch does make the best of the current situation even in
the absence of backpressure. But first and foremost this patch fixes a
(critical) cascading failure that can bring Storm clusters to a halt.
Please correct me if I'm mistaken in my summary.
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