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From "Karthik Kambatla (Commented) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (S4-7) Netty to tolerate network glitches and connection loss
Date Thu, 02 Feb 2012 16:38:53 GMT

    [ https://issues.apache.org/jira/browse/S4-7?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13198935#comment-13198935
] 

Karthik Kambatla commented on S4-7:
-----------------------------------

Matthieu, thanks a lot for taking a close look. I saw the test not running at some point,
but it ran for me the last few times I checked. Now, I see that it surfaces more often if
I increase the number of partitions and/or the number of messages. I ll look into the issue
and fix it at the earliest. 

Just as you suggested, I had initially used a separate queue for in-transit messages. I can
go back to it, but I suspect we would need synchronization across thread pools to avoid multiple
threads processing the same queue. It might make sense to have a single thread sending out
all the messages. Then, we don't need any synchronization at all; however, in cases of connection-loss
to one partition, messages to be sent to other partitions will also be stalled. 
                
> Netty to tolerate network glitches and connection loss
> ------------------------------------------------------
>
>                 Key: S4-7
>                 URL: https://issues.apache.org/jira/browse/S4-7
>             Project: Apache S4
>          Issue Type: Bug
>            Reporter: Leo Neumeyer
>            Assignee: Karthik Kambatla
>             Fix For: 0.5
>
>         Attachments: S4-7-Robust-TCPEmitter-asynchronous-ordered.patch, s4-7.patch, s4-7.patch
>
>
> 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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