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https://issues.apache.org/jira/browse/KAFKA-12257?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Jason Gustafson updated KAFKA-12257:
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Fix Version/s: 3.0.0
> Consumer mishandles topics deleted and recreated with the same name
> --------------------------------------------------------------------
>
> Key: KAFKA-12257
> URL: https://issues.apache.org/jira/browse/KAFKA-12257
> Project: Kafka
> Issue Type: Bug
> Components: consumer
> Affects Versions: 2.7.1, 2.8.1
> Reporter: Ryan Leslie
> Assignee: lqjacklee
> Priority: Blocker
> Fix For: 3.1.0, 3.0.0
>
> Attachments: KAFKA-12257-1.patch, KAFKA-12257.patch
>
>
> In KAFKA-7738, caching of leader epochs (KIP-320) was added to
> o.a.k.c.Metadata to ignore metadata responses with epochs smaller than the
> last seen epoch.
> The current implementation can cause problems in cases where a consumer is
> subscribed to a topic that has been deleted and then recreated with the same
> name. This is something seen more often in consumers that subscribe to a
> multitude of topics using a wildcard.
> Currently, when a topic is deleted and the Fetcher receives
> UNKNOWN_TOPIC_OR_PARTITION, the leader epoch is not cleared. If at a later
> time while the consumer is still running a topic is created with the same
> name, the leader epochs are set to 0 for the new topics partitions, and are
> likely smaller than those for the previous topic. For example, if a broker
> had restarted during the lifespan of the previous topic, the leader epoch
> would be at least 1 or 2. In this case the metadata will be ignored since it
> is incorrectly considered stale. Of course, the user will sometimes get
> lucky, and if a topic was only recently created so that the epoch is still 0,
> no problem will occur on recreation. The issue is also not seen when
> consumers happen to have been restarted in between deletion and recreation.
> The most common side effect of the new metadata being disregarded is that the
> new partitions end up assigned but the Fetcher is unable to fetch data
> because it does not know the leaders. When recreating a topic with the same
> name it is likely that the partition leaders are not the same as for the
> previous topic, and the number of partitions may even be different. Besides
> not being able to retrieve data for the new topic, there is a more sinister
> side effect of the Fetcher triggering a metadata update after the fetch
> fails. The subsequent update will again ignore the topic's metadata if the
> leader epoch is still smaller than the cached value. This metadata refresh
> loop can continue indefinitely and with a sufficient number of consumers may
> even put a strain on a cluster since the requests are occurring in a tight
> loop. This can also be hard for clients to identify since there is nothing
> logged by default that would indicate what's happening. Both the Metadata
> class's logging of "_Not replacing existing epoch_", and the Fetcher's
> logging of "_Leader for partition <T-P> is unknown_" are at DEBUG level.
> A second possible side effect was observed where if the consumer is acting as
> leader of the group and happens to not have any current data for the previous
> topic, e.g. it was cleared due to a metadata error from a broker failure,
> then the new topic's partitions may simply end up unassigned within the
> group. This is because while the subscription list contains the recreated
> topic the metadata for it was previously ignored due to the leader epochs. In
> this case the user would see logs such as:
> {noformat}
> WARN o.a.k.c.c.i.ConsumerCoordinator [Consumer clientId=myClientId,
> groupId=myGroup] The following subscribed topics are not assigned to any
> members: [myTopic]{noformat}
> Interestingly, I believe the Producer is less affected by this problem since
> o.a.k.c.p.i.ProducerMetadata explicitly clears knowledge of its topics in
> retainTopics() after each metadata expiration. ConsumerMetadata does no such
> thing.
> To reproduce this issue:
> # Turn on DEBUG logging, e.g. for org.apache.kafka.clients.consumer and
> org.apache.kafka.clients.Metadata
> # Begin a consumer for a topic (or multiple topics)
> # Restart a broker that happens to be a leader for one of the topic's
> partitions
> # Delete the topic
> # Create another topic with the same name
> # Publish data for the new topic
> # The consumer will not receive data for the new topic, and there will be a
> high rate of metadata requests.
> # The issue can be corrected by restarting the consumer or restarting
> brokers until leader epochs are large enough
> I believe KIP-516 (unique topic ids) will likely fix this problem, since
> after those changes the leader epoch map should be keyed off of the topic id,
> rather than the name.
> One possible workaround with the current version of Kafka is to add code to
> onPartitionsRevoked() to manually clear leader epochs before each rebalance,
> e.g.
> {code:java}
> Map<TopicPartition, Integer> emptyLeaderEpochs = new HashMap<>();
> ConsumerMetadata metadata = (ConsumerMetadata)FieldUtils.readField(consumer,
> "metadata",
> true);
> FieldUtils.writeField(metadata, "lastSeenLeaderEpochs", emptyLeaderEpochs,
> true);{code}
> This is not really recommended of course, since besides modifying private
> consumer state, it defeats the purpose of epochs! It does in a sense revert
> the consumer to pre-2.2 behavior before leader epochs existed.
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