Finding out root cause is definitely something we should do and I hope the
new Java consumer API will not have such issues anymore. Here are my
observation of the issue: the zk retry was caused by session timeout. In
theory the ephemeral node should be removed after the session is terminated
by zk but in fact the node still presented after the session was gone. I
saw lots of slow fsync warning in zk log like below but I am not sure if
the warning has anything to do with the error I encountered.
2015-07-12 22:01:21,195 [myid:2] - WARN [SyncThread:2:FileTxnLog@334] -
fsync-ing the write ahead log in SyncThread:2 took 1023ms which will
adversely effect operation latency. See the ZooKeeper troubleshooting guide
I know in Linkedin ZK is installed on SSD does it help with this?
On Mon, 13 Jul 2015 at 12:50 Mayuresh Gharat <gharatmayures...@gmail.com>
wrote:
> That would solve this. But it looks like a work around. We need to check
> why this happens exactly and get to the root cause. What do you think?
> Getting to the root cause of this might be really useful.
>
> Thanks,
>
> Mayuresh
>
> On Sun, Jul 12, 2015 at 8:45 PM, tao xiao <xiaotao...@gmail.com> wrote:
>
> > Restart the consumers does fix the issue. But since the zk retry is
> wrapped
> > in an infinite loop it doesn't give a chance to consumer to respond it
> > until some one notices and restarts. Why I suggest to have a maximum
> retry
> > policy is if max retry is reached it can invoke a customer handler which
> I
> > can then inject a restart call so that it can remedy itself without
> > people's attention.
> >
> > On Mon, 13 Jul 2015 at 11:36 Jiangjie Qin <j...@linkedin.com.invalid>
> > wrote:
> >
> > > Hi Tao,
> > >
> > > We see this error from time to time but did not think of this as a big
> > > issue. Any reason it bothers you much?
> > > I¹m not sure if throwing exception to user on this exception is a good
> > > handling or not. What are user supposed to do in that case other than
> > > retry?
> > >
> > > Thanks,
> > >
> > > Jiangjie (Becket) Qin
> > >
> > > On 7/12/15, 7:16 PM, "tao xiao" <xiaotao...@gmail.com> wrote:
> > >
> > > >We saw the error again in our cluster. Anyone has the same issue
> > before?
> > > >
> > > >On Fri, 10 Jul 2015 at 13:26 tao xiao <xiaotao...@gmail.com> wrote:
> > > >
> > > >> Bump the thread. Any help would be appreciated.
> > > >>
> > > >> On Wed, 8 Jul 2015 at 20:09 tao xiao <xiaotao...@gmail.com> wrote:
> > > >>
> > > >>> Additional info
> > > >>> Kafka version: 0.8.2.1
> > > >>> zookeeper: 3.4.6
> > > >>>
> > > >>> On Wed, 8 Jul 2015 at 20:07 tao xiao <xiaotao...@gmail.com> wrote:
> > > >>>
> > > >>>> Hi team,
> > > >>>>
> > > >>>> I have 10 high level consumers connecting to Kafka and one of them
> > > >>>>kept
> > > >>>> complaining "conflicted ephemeral node" for about 8 hours. The log
> > was
> > > >>>> filled with below exception
> > > >>>>
> > > >>>> [2015-07-07 14:03:51,615] INFO conflict in
> > > >>>> /consumers/group/ids/test-1435856975563-9a9fdc6c data:
> > > >>>>
> > >
> >
> >>>>{"version":1,"subscription":{"test.*":1},"pattern":"white_list","timest
> > > >>>>amp":"1436275631510"}
> > > >>>> stored data:
> > > >>>>
> > >
> >
> >>>>{"version":1,"subscription":{"test.*":1},"pattern":"white_list","timest
> > > >>>>amp":"1436275558570"}
> > > >>>> (kafka.utils.ZkUtils$)
> > > >>>> [2015-07-07 14:03:51,616] INFO I wrote this conflicted ephemeral
> > node
> > > >>>>
> > >
> >
> >>>>[{"version":1,"subscription":{"test.*":1},"pattern":"white_list","times
> > > >>>>tamp":"1436275631510"}]
> > > >>>> at /consumers/group/ids/test-1435856975563-9a9fdc6c a while back
> in
> > a
> > > >>>> different session, hence I will backoff for this node to be
> deleted
> > by
> > > >>>> Zookeeper and retry (kafka.utils.ZkUtils$)
> > > >>>>
> > > >>>> In the meantime zookeeper reported below exception for the same
> time
> > > >>>>span
> > > >>>>
> > > >>>> 2015-07-07 22:45:09,687 [myid:3] - INFO [ProcessThread(sid:3
> > > >>>> cport:-1)::PrepRequestProcessor@645] - Got user-level
> > KeeperException
> > > >>>> when processing sessionid:0x44e657ff19c0019 type:create
> cxid:0x7a26
> > > >>>> zxid:0x3015f6e77 txntype:-1 reqpath:n/a Error
> > > >>>> Path:/consumers/group/ids/test-1435856975563-9a9fdc6c
> > > >>>>Error:KeeperErrorCode
> > > >>>> = NodeExists for /consumers/group/ids/test-1435856975563-9a9fdc6c
> > > >>>>
> > > >>>> At the end zookeeper timed out the session and consumers triggered
> > > >>>> rebalance.
> > > >>>>
> > > >>>> I know that conflicted ephemeral node warning is to handle a
> > zookeeper
> > > >>>> bug that session expiration and ephemeral node deletion are not
> done
> > > >>>> atomically but as indicated from zookeeper log the zookeeper never
> > > >>>>got a
> > > >>>> chance to delete the ephemeral node which made me think that the
> > > >>>>session
> > > >>>> was not expired at that time. And for some reason zookeeper fired
> > > >>>>session
> > > >>>> expire event which subsequently invoked ZKSessionExpireListener.
> I
> > > >>>>was
> > > >>>> just wondering if anyone have ever encountered similar issue
> before
> > > >>>>and
> > > >>>> what I can do at zookeeper side to prevent this?
> > > >>>>
> > > >>>> Another problem is that
> createEphemeralPathExpectConflictHandleZKBug
> > > >>>> call is wrapped in a while(true) loop which runs forever until the
> > > >>>> ephemeral node is created. Would it be better that we can employ
> an
> > > >>>> exponential retry policy with a max number of retries so that it
> > has a
> > > >>>> chance to re-throw the exception back to caller and let caller
> > handle
> > > >>>>it in
> > > >>>> situation like above?
> > > >>>>
> > > >>>>
> > >
> > >
> >
>
>
>
> --
> -Regards,
> Mayuresh R. Gharat
> (862) 250-7125
>
