[jira] [Resolved] (KAFKA-7873) KafkaBasedLog's consumer should always seek to beginning when starting

["Jason Gustafson (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/KAFKA-7873?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Jason Gustafson resolved KAFKA-7873.
------------------------------------
       Resolution: Fixed
    Fix Version/s: 2.0.2
                   2.1.1
                   2.2.0

> KafkaBasedLog's consumer should always seek to beginning when starting
> ----------------------------------------------------------------------
>
>                 Key: KAFKA-7873
>                 URL: https://issues.apache.org/jira/browse/KAFKA-7873
>             Project: Kafka
>          Issue Type: Bug
>          Components: KafkaConnect
>    Affects Versions: 2.1.0
>            Reporter: Randall Hauch
>            Assignee: Randall Hauch
>            Priority: Critical
>             Fix For: 2.2.0, 2.1.1, 2.0.2
>
>
> KafkaBasedLog expects that callers set the `group.id` for the consumer configuration, and does not itself set the `group.id` if the caller does not explicitly do so. However, [KIP-289|https://cwiki.apache.org/confluence/display/KAFKA/KIP-289%3A+Improve+the+default+group+id+behavior+in+KafkaConsumer] changed the default for the `group.id` from a blank string to be null, which changes how KafkaBasedLog behaves when no `group.id` is set, and it actually deprecates and issues a warning when no `group.id` is specified.
> When KafkaBasedLog starts up, it should always start from the beginning of the topic and consume to the end. The consumer's logic for where to start is always:
> # explicit seek
> # committed offset (skipped if group.id is null)
> # auto reset behavior
> and currently Connect does not explicitly seek to the beginning and instead relies upon `auto.offset.reset=earliest`. However, if a `group.id` is specified *ant* there are committed offsets, then the consumer will start from the committed offsets rather than from the beginning. If a 'group.id' is not specified, then the auto reset behavior should work.
> However, to avoid the warning and possible exception when no `group.id` is specified, KafkaBasedLog should always call {{consumer.seekToBeginning()}} during startup. 



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