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From Mahadev Konar <maha...@yahoo-inc.com>
Subject Re: Using zookeeper to assign a bunch of long-running tasks to nodes (without unhandled tasks and double-handled tasks)
Date Tue, 26 Jan 2010 03:23:04 GMT
 That's a good point, for 2) the application certainly needs to know that
CONNECTIONLOSS has happened and it cannot connect to any of the servers.
After spending some time on ZOOKEEPER-22, I am a little concerned about how
much ZOOKEEPER-22 can do. I will post my thoughts/findings/concerns on the
jira and you are welcome to give your feedback.


On 1/25/10 7:12 PM, "Qing Yan" <qingyan@gmail.com> wrote:

> Hi Ted,
>   Thank you for the detail explaination, it clarify things alot, my
> understanding there two types of CONNECTION_LOSS:
> 1) Lose connection with one ZK server, failover to anther one successfully.
> No big deal, connection to the (quorum of) ZK cluster is preserved.
> 2) Lose connection with the (quorum of) ZK cluster, e.g. C3 as mentioned
> before. if the situation continues will lead to CONNECTION_EXPIRE.
> I totally concur case 1) should be made transparent to the application, if
> ZK-22 can eliminate this, it will be great.
> About case 2), seems to me there is indeed a need for application to know
> about this, per ZK documentation :
> When you disconnect from a server (for example, when the server fails), you
> will not get any watches until the connection is reestablished. For this
> reason session events are sent to all outstanding watch handlers. Use
> session events to go into a safe mode: you will not be receiving events
> while disconnected, so your process should act conservatively in that mode.
> http://hadoop.apache.org/zookeeper/docs/r3.2.2/zookeeperProgrammers.html
> But from reading your post, it seems that case 2) will no longer be reported
> to application, hence the confusion.
>  In any case, I think the documentation needs to be updated to reflect the
> latest design/contract change.

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