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https://issues.apache.org/jira/browse/KAFKA-1475?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14017849#comment-14017849
]
Guozhang Wang commented on KAFKA-1475:
--------------------------------------
Hello Hang,
Yes we are aware of of this issue, but in zkClient 0.3 there is no API to get
the session ID, so we tried to use the timestamp in the znode as a walk-around
solution in 0.8.1, such that if the previous znode is written by an older
session its timestamp should be different. You can try to upgrade to 0.8.1.1 to
see if this issue has gone away for you.
---
def createEphemeralPathExpectConflictHandleZKBug(zkClient: ZkClient, path:
String, data: String, expectedCallerData: Any, checker: (String, Any) =>
Boolean, backoffTime: Int): Unit = {
while (true) {
try {
createEphemeralPathExpectConflict(zkClient, path, data)
return
} catch {
case e: ZkNodeExistsException => {
// An ephemeral node may still exist even after its corresponding
session has expired
// due to a Zookeeper bug, in this case we need to retry writing
until the previous node is deleted
// and hence the write succeeds without ZkNodeExistsException
ZkUtils.readDataMaybeNull(zkClient, path)._1 match {
case Some(writtenData) => {
if (checker(writtenData, expectedCallerData)) {
info("I wrote this conflicted ephemeral node [%s] at %s a while
back in a different session, ".format(data, path)
+ "hence I will backoff for this node to be deleted by
Zookeeper and retry")
Thread.sleep(backoffTime)
} else {
throw e
}
}
case None => // the node disappeared; retry creating the ephemeral
node immediately
}
}
case e2: Throwable => throw e2
}
}
}
---
> Kafka consumer stops LeaderFinder/FetcherThreads, but application does not
> know
> -------------------------------------------------------------------------------
>
> Key: KAFKA-1475
> URL: https://issues.apache.org/jira/browse/KAFKA-1475
> Project: Kafka
> Issue Type: Bug
> Components: clients, consumer
> Affects Versions: 0.8.0
> Environment: linux, rhel 6.4
> Reporter: Hang Qi
> Assignee: Neha Narkhede
> Labels: consumer
> Attachments: 5055aeee-zk.txt
>
>
> We encounter an issue of consumers not consuming messages in production. (
> this consumer has its own consumer group, and just consumes one topic of 3
> partitions.)
> Based on the logs, we have following findings:
> 1. Zookeeper session expires, kafka highlevel consumer detected this event,
> and released old broker parition ownership and re-register consumer.
> 2. Upon creating ephemeral path in Zookeeper, it found that the path still
> exists, and try to read the content of the node.
> 3. After read back the content, it founds the content is same as that it is
> going to write, so it logged as "[ZkClient-EventThread-428-ZK/kafka]
> (kafka.utils.ZkUtils$) -
> /consumers/consumerA/ids/consumerA-1400815740329-5055aeee exists with value {
> "pattern":"static", "subscription":{ "TOPIC": 1},
> "timestamp":"1400846114845", "version":1 } during connection loss; this is
> ok", and doing nothing.
> 4. After that, it throws exception indicated that the cause is
> "org.apache.zookeeper.KeeperException$NoNodeException: KeeperErrorCode =
> NoNode for /consumers/consumerA/ids/consumerA-1400815740329-5055aeee" during
> rebalance.
> 5. After all retries failed, it gave up retry and left the
> LeaderFinderThread, FetcherThread stopped.
> Step 3 looks very weird, checking the code, there is timestamp contains in
> the stored data, it may be caused by Zookeeper issue.
> But what I am wondering is that whether it is possible to let application
> (kafka client users) to know that the underline LeaderFinderThread and
> FetcherThread are stopped, like allowing application to register some
> callback or throws some exception (by invalidate the KafkaStream iterator for
> example)? For me, it is not reasonable for the kafka client to shutdown
> everything and wait for next rebalance, and let application wait on
> iterator.hasNext() without knowing that there is something wrong underline.
> I've read about twiki about kafka 0.9 consumer rewrite, and there is a
> ConsumerRebalanceCallback interface, but I am not sure how long it will take
> to be ready, and how long it will take for us to migrate.
> Please help to look at this issue. Thanks very much!
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