Github user miguno commented on the pull request:
https://github.com/apache/storm/pull/566#issuecomment-106795826
> My reasoning is as follows:
>
> * One has three option to deal with Netty's buffer filling up:
> 1. Discard incoming new messages
> 2. Block client thread until there is space (back pressure)
> 3. Keep buffering up until OOME is thrown
>
> My guess is that the v0.9.4 code attempted to implement option (i), but
actually the behavior is option (iii).
The code's intention was actually (iii). As you described back pressure
(ii) was not picked because this will require a significant amount of work,
which was thus out of scope for fixing STORM-329. The reason (iii) was
preferred over (i) was also as you described -- if (and only if) users have
enabled acking = guaranteed message processing for a topology, they can prevent
OOM errors from happening by setting
[`topology.max.spout.pending`](https://github.com/apache/storm/blob/master/conf/defaults.yaml#L180).
I'll have to look at your code in more detail before commenting. I'll also
ping @ptgoetz, @clockfly, @tedxia, and @revans2 who were involved in this
significant patch (sorry for the spam, folks!).
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