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Date: Tue, 16 Mar 2010 11:22:39 -0700
From: Patrick Hunt <phunt@apache.org>
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To: zookeeper-user@hadoop.apache.org
Subject: Re: permanent ZSESSIONMOVED
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Łukasz Osipiuk wrote:
> On Tue, Mar 16, 2010 at 17:18, Patrick Hunt <phunt@apache.org> wrote:
>> Can you verify that you are using 3.2.2 on all servers? You can do this by
>> running the "stat" command against each of your servers and look at the very
>> top of the output (we include the version of zk server there).
>> http://bit.ly/dglVld
> 
> Thanks for hint.
> 
> We had 3.2.2 jars installed on all server - I checked it previously
> but apparently our script which restarts instance
> after installing .deb does not work very well and node2 and node3 were
> running version 3.2.1.
> Could using 3.2.1 be source of the problem?
> 

I heard this story where customer service for dell asks customers to 
replug in the mouse because it might be "a dusty connection". Invariably 
when ppl look at the back of the box they find that the mouse is not 
actually plugged in. Brilliant ideas from CS perspective. ;-)

I think that issue was fixed in 3.2.1, so I don't think that's an issue 
(version).

>> Are you using synchronous or async operations in your client?
> 
> We are only using async operations.

Ok. good info.

> 
>> I see snippets from the server logs, but I don't see anything from you
>> client logs. It would really help if you could zip up all the logs (server
>> and client) and provide them.
> 
> We do not really have much logging on application side :(. Failed
> operations are logged with error code (ZSESSIONEXPIRED in our case).
> We also log session state changes but we noticed only changes between 1 and 3.
> Unfortunately we do not have logs coming directly from zookeeper
> library as it logs to stderr/stdout and we do not store any of them at
> the moment.
> 

I see, in this case I think that the log messages theyselves are the 
problem, ie we are warning about this, but it's not a real problem. We 
warn on things that we don't like but can handle, we error if we 
don'tlike/can'thandle.

MOVED basically means that a client initiated a request on one server, 
then moved to another server before the request could be processed.

In your case you are using async requests, that can actually make this 
problem show up more (more "in flight" requests vs sync operation).

So if you are not seeing MOVED on the client then this is fine. If you 
see them in the server log it means what I said above.

That make sense, or am I missing something?


Patrick


> Regards, Łukasz
> 
>> Patrick
>>
>> Łukasz Osipiuk wrote:
>>> not really - it happens occasionally - every few days :(
>>> I believe it is somewhat connected with our network environment which
>>> suffers from some packet loss which leads to
>>> connection timeouts.
>>>
>>> I can switch on some more logging if you can lead me which categories
>>> are worth to enable DEBUG for them.
>>>
>>> Regards, Łukasz Osipiuk
>>>
>>> On Tue, Mar 16, 2010 at 16:35, Benjamin Reed <breed@yahoo-inc.com> wrote:
>>>> weird, this does sound like a bug. do you have a reliable way of
>>>> reproducing
>>>> the problem?
>>>>
>>>> thanx
>>>> ben
>>>>
>>>> On 03/16/2010 08:27 AM, Łukasz Osipiuk wrote:
>>>>> nope.
>>>>>
>>>>> I always pass 0 as clientid.
>>>>>
>>>>> Łukasz
>>>>>
>>>>> On Tue, Mar 16, 2010 at 16:20, Benjamin Reed<breed@yahoo-inc.com>
>>>>>  wrote:
>>>>>
>>>>>> do you ever use zookeeper_init() with the clientid field set to
>>>>>> something
>>>>>> other than null?
>>>>>>
>>>>>> ben
>>>>>>
>>>>>> On 03/16/2010 07:43 AM, Łukasz Osipiuk wrote:
>>>>>>
>>>>>>> Hi everyone!
>>>>>>>
>>>>>>> I am writing to this group because recently we are getting some
>>>>>>> strange errors with our production zookeeper setup.
>>>>>>>
>>>>>>>  From time to time we are observing that our client application (C++
>>>>>>> based) disconnects from zookeeper (session state is changed to 1) and
>>>>>>> reconnects (state changed to 3).
>>>>>>> This itself is not a problem - usually application continues to run
>>>>>>> without problems after reconnect.
>>>>>>> But from time to time after above happens all subsequent operations
>>>>>>> start to return ZSESSIONMOVED error. To make it work again we have to
>>>>>>> restart application (which creates new zookeeper session).
>>>>>>>
>>>>>>> I noticed that in 3.2.0 introduced a bug
>>>>>>> http://issues.apache.org/jira/browse/ZOOKEEPER-449 but we are using
>>>>>>> zookeeper v. 3.2.2.
>>>>>>> I just noticed that app at compile time used 3.2.0 library but patches
>>>>>>> fixing bug 449 did not touch C client lib so I believe that our
>>>>>>> problems are not
>>>>>>> related with that.
>>>>>>>
>>>>>>> In zookeeper logs at moment which initiated the problem with client
>>>>>>> application I have
>>>>>>>
>>>>>>> node1:
>>>>>>> 2010-03-16 14:21:43,510 - INFO
>>>>>>> [NIOServerCxn.Factory:2181:NIOServerCnxn@607] - Connected to
>>>>>>> /10.1.112.61:37197 lastZxid 42992576502
>>>>>>> 2010-03-16 14:21:43,510 - INFO
>>>>>>> [NIOServerCxn.Factory:2181:NIOServerCnxn@636] - Renewing session
>>>>>>> 0x324dcc1ba580085
>>>>>>> 2010-03-16 14:21:49,443 - INFO
>>>>>>> [QuorumPeer:/0:0:0:0:0:0:0:0:2181:NIOServerCnxn@992] - Finished init
>>>>>>> of 0x324dcc1ba580085 valid:true
>>>>>>> 2010-03-16 14:21:49,443 - WARN
>>>>>>> [NIOServerCxn.Factory:2181:NIOServerCnxn@518] - Exception causing
>>>>>>> close of session 0x324dcc1ba580085 due to java.io.IOException: Read
>>>>>>> error
>>>>>>> 2010-03-16 14:21:49,444 - INFO
>>>>>>> [NIOServerCxn.Factory:2181:NIOServerCnxn@857] - closing
>>>>>>> session:0x324dcc1ba580085 NIOServerCnxn:
>>>>>>> java.nio.channels.SocketChannel[connected local=/10.1.112.62:2181
>>>>>>> remote=/10.1.112.61:37197]
>>>>>>>
>>>>>>> node2:
>>>>>>> 2010-03-16 14:21:40,580 - WARN
>>>>>>> [NIOServerCxn.Factory:2181:NIOServerCnxn@494] - Exception causing
>>>>>>> close of session 0x324dcc1ba580085 due to java.io.IOException: Read
>>>>>>> error
>>>>>>> 2010-03-16 14:21:40,581 - INFO
>>>>>>> [NIOServerCxn.Factory:2181:NIOServerCnxn@833] - closing
>>>>>>> session:0x324dcc1ba580085 NIOServerCnxn:
>>>>>>> java.nio.channels.SocketChannel[connected local=/10.1.112.63:2181
>>>>>>> remote=/10.1.112.61:60693]
>>>>>>> 2010-03-16 14:21:46,839 - INFO
>>>>>>> [NIOServerCxn.Factory:2181:NIOServerCnxn@583] - Connected to
>>>>>>> /10.1.112.61:48336 lastZxid 42992576502
>>>>>>> 2010-03-16 14:21:46,839 - INFO
>>>>>>> [NIOServerCxn.Factory:2181:NIOServerCnxn@612] - Renewing session
>>>>>>> 0x324dcc1ba580085
>>>>>>> 2010-03-16 14:21:49,439 - INFO
>>>>>>> [QuorumPeer:/0:0:0:0:0:0:0:0:2181:NIOServerCnxn@964] - Finished init
>>>>>>> of 0x324dcc1ba580085 valid:true
>>>>>>>
>>>>>>> node3:
>>>>>>> 2010-03-16 02:14:48,961 - WARN
>>>>>>> [NIOServerCxn.Factory:2181:NIOServerCnxn@494] - Exception causing
>>>>>>> close of session 0x324dcc1ba580085 due to java.io.IOException: Read
>>>>>>> error
>>>>>>> 2010-03-16 02:14:48,962 - INFO
>>>>>>> [NIOServerCxn.Factory:2181:NIOServerCnxn@833] - closing
>>>>>>> session:0x324dcc1ba580085 NIOServerCnxn:
>>>>>>> java.nio.channels.SocketChannel[connected local=/10.1.112.64:2181
>>>>>>> remote=/10.1.112.61:57309]
>>>>>>>
>>>>>>> and then lots of entries like this
>>>>>>> 2010-03-16 02:14:54,696 - WARN
>>>>>>> [ProcessThread:-1:PrepRequestProcessor@402] - Got exception when
>>>>>>> processing sessionid:0x324dcc1ba580085 type:create cxid:0x4b9e9e49
>>>>>>> zxid:0xfffffffffffffffe txntype:unknown
>>>>>>> /locks/9871253/lock-8589943989-
>>>>>>> org.apache.zookeeper.KeeperException$SessionMovedException:
>>>>>>> KeeperErrorCode = Session moved
>>>>>>>        at
>>>>>>>
>>>>>>>
>>>>>>> org.apache.zookeeper.server.SessionTrackerImpl.checkSession(SessionTrackerImpl.java:231)
>>>>>>>        at
>>>>>>>
>>>>>>>
>>>>>>> org.apache.zookeeper.server.PrepRequestProcessor.pRequest(PrepRequestProcessor.java:211)
>>>>>>>        at
>>>>>>>
>>>>>>>
>>>>>>> org.apache.zookeeper.server.PrepRequestProcessor.run(PrepRequestProcessor.java:114)
>>>>>>> 2010-03-16 14:22:06,428 - WARN
>>>>>>> [ProcessThread:-1:PrepRequestProcessor@402] - Got exception when
>>>>>>> processing sessionid:0x324dcc1ba580085 type:create cxid:0x4b9f6603
>>>>>>> zxid:0xfffffffffffffffe txntype:unknown
>>>>>>> /locks/1665960/lock-8589961006-
>>>>>>> org.apache.zookeeper.KeeperException$SessionMovedException:
>>>>>>> KeeperErrorCode = Session moved
>>>>>>>        at
>>>>>>>
>>>>>>>
>>>>>>> org.apache.zookeeper.server.SessionTrackerImpl.checkSession(SessionTrackerImpl.java:231)
>>>>>>>        at
>>>>>>>
>>>>>>>
>>>>>>> org.apache.zookeeper.server.PrepRequestProcessor.pRequest(PrepRequestProcessor.java:211)
>>>>>>>        at
>>>>>>>
>>>>>>>
>>>>>>> org.apache.zookeeper.server.PrepRequestProcessor.run(PrepRequestProcessor.java:114)
>>>>>>>
>>>>>>>
>>>>>>> To workaround disconnections I am going to increase session timeout
>>>>>>> from 5 to 15 seconds but event if it helps at all it is just a
>>>>>>> workaround.
>>>>>>>
>>>>>>> Do you have an idea where is the source of my problem.
>>>>>>>
>>>>>>> Regards, Łukasz Osipiuk
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>
>>>
>>>
> 
> 
>