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From Michael Bauland <Michael.Baul...@knipp.de>
Subject Re: question regarding connectionloss
Date Tue, 02 Feb 2010 07:36:08 GMT
Hi Ted,

thanks for your reply.

> This page: about Zookeeper error
> handling<http://wiki.apache.org/hadoop/ZooKeeper/ErrorHandling>may
> help.

I actually read this page before. You may have misunderstood my
question. I know how to recover from the connectionloss exception. I was
just curious why it occurred so often in my described scenario. I would
have assumed that in that scenario it shouldn't occur at all, but it was
almost half of the requests that returned with a connectionloss.



> On Mon, Feb 1, 2010 at 4:30 AM, Michael Bauland <Michael.Bauland@knipp.de>wrote:
>> Hello,
>> I've got a question regarding the connectionloss exception thrown by Java.
>> I've got an ensemble running with three zk servers. If one of the three
>> servers is not running, the whole ensemble should still work (and it
>> does, so that's fine). But in this situation I experience quite often a
>> connectionloss exception and I'm wondering if I'm doing something wrong
>> or if that's to be expected.
>> My Code is rather simple:
>> I create a new connection to my ensemble using
>> ZooKeeper zk = new ZooKeeper (connectString, timeOut, new MyWatcher ());
>> where connectString contains all three servers. Then I use the ZooKeeper
>> to read data from a certain path:
>> zk.getData (path, false, null);
>> This call quite often returns an exception like
>> org.apache.zookeeper.KeeperException$ConnectionLossException:
>> KeeperErrorCode = ConnectionLoss for /125/170/test
>> But according to your documentation, the connectionloss exception should
>> only occur in the following two cases:
>>>    1. The application calls an operation on a session that is no longer
>> alive/valid
>> This should not be the case, since I only just created the session.
>>>    2. The ZooKeeper client disconnects from a server when there are
>> pending operations to that server, i.e., there is a pending asynchronous
>> call.
>> The should also not be the case. I was just doing a read request and no
>> other client was accessing the ensemble.
>> My only idea is that maybe the connection call first tried to connect to
>>  the zookeeper server that was not running (remember only two of the
>> three servers are running) and before it had a chance to try to connect
>> to one of the other servers, my getData call was made and failed with
>> connectionloss. Could that be the reason?
>> But I thought the connection handling was automatic and if a connection
>> failed the client would automatically try any of the other listed
>> servers without the user noticing!?
>> Thanks for any help.
>> Cheers,
>> Michael
>> --
>> Michael Bauland
>> michael.bauland@knipp.de
>> bauland.tel

Michael Bauland

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