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https://issues.apache.org/jira/browse/KAFKA-7096?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Dong Lin resolved KAFKA-7096.
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Resolution: Fixed
> Consumer should drop the data for unassigned topic partitions
> -------------------------------------------------------------
>
> Key: KAFKA-7096
> URL: https://issues.apache.org/jira/browse/KAFKA-7096
> Project: Kafka
> Issue Type: Improvement
> Reporter: Mayuresh Gharat
> Assignee: Mayuresh Gharat
> Priority: Major
> Fix For: 2.2.0
>
>
> currently if a client has assigned topics : T1, T2, T3 and calls poll(), the
> poll might fetch data for partitions for all 3 topics T1, T2, T3. Now if the
> client unassigns some topics (for example T3) and calls poll() we still hold
> the data (for T3) in the completedFetches queue until we actually reach the
> buffered data for the unassigned Topics (T3 in our example) on subsequent
> poll() calls, at which point we drop that data. This process of holding the
> data is unnecessary.
> When a client creates a topic, it takes time for the broker to fetch ACLs for
> the topic. But during this time, the client will issue fetchRequest for the
> topic, it will get response for the partitions of this topic. The response
> consist of TopicAuthorizationException for each of the partitions. This
> response for each partition is wrapped with a completedFetch and added to the
> completedFetches queue. Now when the client calls the next poll() it sees the
> TopicAuthorizationException from the first buffered CompletedFetch. At this
> point the client chooses to sleep for 1.5 min as a backoff (as per the
> design), hoping that the Broker fetches the ACL from ACL store in the
> meantime. Actually the Broker has already fetched the ACL by this time. When
> the client calls poll() after the sleep, it again sees the
> TopicAuthorizationException from the second completedFetch and it sleeps
> again. So it takes (1.5 * 60 * partitions) seconds before the client can see
> any data. With this patch, the client when it sees the first
> TopicAuthorizationException, it can all assign(EmptySet), which will get rid
> of the buffered completedFetches (those with TopicAuthorizationException) and
> it can again call assign(TopicPartitions) before calling poll(). With this
> patch we found that client was able to get the records as soon as the Broker
> fetched the ACLs from ACL store.
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