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From "Karthik Kambatla (Commented) (JIRA)" <>
Subject [jira] [Commented] (S4-7) Netty to tolerate network glitches and connection loss
Date Fri, 09 Dec 2011 04:23:39 GMT


Karthik Kambatla commented on S4-7:

To ensure we don't loose messages on the wire, we should maintain a queue for each channel
and when the ChannelFuture reports success, dequeue the first message in the queue. 

Given we already have another queue for incoming messages to tolerate network glitches, would
it make sense to have a single queue for both and have a separate thread (pool) for going
to send the events in these per-channel message queues.

The NettyEmitter would change as follows:
1. We maintain one bounded messageQueue per partition
2. send() always queues the message to the messageQueue and returns
3. Another thread (pool) sifts through each messageQueue in round-robin fashion and sends
these messages - dequeues messages on ChannelFuture.success()
4. For extended functionality, send() can allow registering a callback to confirm to the client
(of NettyEmitter) that the message has been sent

> Netty to tolerate network glitches and connection loss
> ------------------------------------------------------
>                 Key: S4-7
>                 URL:
>             Project: Apache S4
>          Issue Type: Bug
>            Reporter: Leo Neumeyer
>            Assignee: Karthik Kambatla
>             Fix For: 0.5
> NettyEmitter connects to different partitions and creates channels over which it communicates
to other listeners.
> It suffers from the following issues -- 
> 1. If the underlying topology changes, the channels and the associated connections are
not updated.
> 2. If a connection gets disconnected, it stays disconnected.
> 3. If for any reason, a connection can't be made, send() drops the message to be sent.
> The solution is to - 
> 1. Maintain a bounded messageQueue for each destination partition - if a connection does
not exist, the message should be queued.
> 2. Maintain a map of the channel used for each destination partition - update this map
on changes to topology, or on send() in case of disconnections.
> 3. Every time a (re-)connection is made, send the queued messages first.

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