[jira] [Created] (KAFKA-1387) Kafka getting stuck creating ephemeral node it has already created when two zookeeper sessions are established in a very short period of time

["Fedor Korotkiy (JIRA)" <ji...@apache.org>]

Fedor Korotkiy created KAFKA-1387:
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             Summary: Kafka getting stuck creating ephemeral node it has already created when two zookeeper sessions are established in a very short period of time
                 Key: KAFKA-1387
                 URL: https://issues.apache.org/jira/browse/KAFKA-1387
             Project: Kafka
          Issue Type: Bug
            Reporter: Fedor Korotkiy


Kafka broker re-registers itself in zookeeper every time handleNewSession() callback is invoked.

https://github.com/apache/kafka/blob/0.8.1/core/src/main/scala/kafka/server/KafkaHealthcheck.scala 

Now imagine the following sequence of events.
1) Zookeeper session reestablishes. handleNewSession() callback is queued by the zkClient, but not invoked yet.
2) Zookeeper session reestablishes again, queueing callback second time.
3) First callback is invoked, creating /broker/[id] ephemeral path.
4) Second callback is invoked and it tries to create /broker/[id] path using createEphemeralPathExpectConflictHandleZKBug() function. But the path is already exists, so createEphemeralPathExpectConflictHandleZKBug() is getting stuck in the infinite loop.

Seems like controller election code have the same issue.

I'am able to reproduce this issue on the 0.8.1 branch from github using the following configs.

# zookeeper
tickTime=10
dataDir=/tmp/zk/
clientPort=2101
maxClientCnxns=0

# kafka
broker.id=1
log.dir=/tmp/kafka
zookeeper.connect=localhost:2101

zookeeper.connection.timeout.ms=100
zookeeper.sessiontimeout.ms=100

Just start kafka and zookeeper and then pause zookeeper several times using Ctrl-Z.



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