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https://issues.apache.org/jira/browse/KAFKA-6098?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16212990#comment-16212990
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Guozhang Wang commented on KAFKA-6098:
--------------------------------------
I think the reason this race condition gap gets "bigger" is that, when we park
the delayed delete topic request we set the complete criterion as "local
metadata gets updated to remove this topic". I.e. once the update metadata
request gets received, this delayed delete topic gets returned immediately.
Our Javadoc of the admin client actually claims this behavior:
{code}
* It may take several seconds after AdminClient#deleteTopics returns
* success for all the brokers to become aware that the topics are gone.
* During this time, AdminClient#listTopics and AdminClient#describeTopics
* may continue to return information about the deleted topics.
{code}
But the problem is that, even when AdminClient#listTopics does not return the
topic any more, the deletion process may still not 100% complete; so after the
listTopics check if a following create topic request get "TOPIC EXISTED", we
cannot tell if this is transient (i.e. the topic will be gone later) or
permanent, so either finite/infinite retrying or moving on is not perfect.
> Delete and Re-create topic operation could result in race condition
> -------------------------------------------------------------------
>
> Key: KAFKA-6098
> URL: https://issues.apache.org/jira/browse/KAFKA-6098
> Project: Kafka
> Issue Type: Bug
> Reporter: Guozhang Wang
>
> Here is the following process to re-produce this issue:
> 1. Delete a topic using the delete topic request.
> 2. Confirm the topic is deleted using the list topics request.
> 3. Create the topic using the create topic request.
> In step 3) a race condition can happen that the response returns a
> {{TOPIC_ALREADY_EXISTS}} error code, indicating the topic has already existed.
> The root cause of the above issue is in the {{TopicDeletionManager}} class:
> {code}
> controller.partitionStateMachine.handleStateChanges(partitionsForDeletedTopic.toSeq,
> OfflinePartition)
> controller.partitionStateMachine.handleStateChanges(partitionsForDeletedTopic.toSeq,
> NonExistentPartition)
> topicsToBeDeleted -= topic
> partitionsToBeDeleted.retain(_.topic != topic)
> kafkaControllerZkUtils.deleteTopicZNode(topic)
> kafkaControllerZkUtils.deleteTopicConfigs(Seq(topic))
> kafkaControllerZkUtils.deleteTopicDeletions(Seq(topic))
> controllerContext.removeTopic(topic)
> {code}
> I.e. it first update the broker's metadata cache through the ISR and metadata
> update request, then delete the topic zk path, and then delete the
> topic-deletion zk path. However, upon handling the create topic request, the
> broker will simply try to write to the topic zk path directly. Hence there is
> a race condition that between brokers update their metadata cache (hence list
> topic request not returning this topic anymore) and zk path for the topic be
> deleted (hence the create topic succeed).
> The reason this problem could be exposed, is through current handling logic
> of the create topic response, most of which takes {{TOPIC_ALREADY_EXISTS}} as
> "OK" and moves on, and the zk path will be deleted later, hence leaving the
> topic to be not created at all:
> https://github.com/apache/kafka/blob/249e398bf84cdd475af6529e163e78486b43c570/streams/src/main/java/org/apache/kafka/streams/processor/internals/StreamsKafkaClient.java#L221
> https://github.com/apache/kafka/blob/1a653c813c842c0b67f26fb119d7727e272cf834/connect/runtime/src/main/java/org/apache/kafka/connect/util/TopicAdmin.java#L232
> Looking at the code history, it seems this race condition always exist, but
> testing on trunk / 1.0 with the above steps it is more likely to happen than
> before. I wonder if the ZK async calls have an effect here. cc [~junrao]
> [~onurkaraman]
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