[jira] [Updated] (KAFKA-7026) Sticky assignor could assign a partition to multiple consumers

["Vahid Hashemian (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/KAFKA-7026?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Vahid Hashemian updated KAFKA-7026:
-----------------------------------
    Labels: kip  (was: )

> Sticky assignor could assign a partition to multiple consumers
> --------------------------------------------------------------
>
>                 Key: KAFKA-7026
>                 URL: https://issues.apache.org/jira/browse/KAFKA-7026
>             Project: Kafka
>          Issue Type: Bug
>          Components: clients
>            Reporter: Vahid Hashemian
>            Assignee: Vahid Hashemian
>            Priority: Major
>              Labels: kip
>             Fix For: 2.1.0
>
>
> In the following scenario sticky assignor assigns a topic partition to two consumers in the group:
>  # Create a topic {{test}} with a single partition
>  # Start consumer {{c1}} in group {{sticky-group}} ({{c1}} becomes group leader and gets {{test-0}})
>  # Start consumer {{c2}}  in group {{sticky-group}} ({{c1}} holds onto {{test-0}}, {{c2}} does not get any partition) 
>  # Pause {{c1}} (e.g. using Java debugger) ({{c2}} becomes leader and takes over {{test-0}}, {{c1}} leaves the group)
>  # Resume {{c1}}
> At this point both {{c1}} and {{c2}} will have {{test-0}} assigned to them.
>  
> The reason is {{c1}} still has kept its previous assignment ({{test-0}}) from the last assignment it received from the leader (itself) and did not get the next round of assignments (when {{c2}} became leader) because it was paused. Both {{c1}} and {{c2}} enter the rebalance supplying {{test-0}} as their existing assignment. The sticky assignor code does not currently check and avoid this duplication.
>  
> Note: This issue was originally reported on [StackOverflow|https://stackoverflow.com/questions/50761842/kafka-stickyassignor-breaking-delivery-to-single-consumer-in-the-group].



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