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https://issues.apache.org/jira/browse/KAFKA-14347?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17627365#comment-17627365
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Vincent Jiang commented on KAFKA-14347:
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Related issue: https://issues.apache.org/jira/browse/KAFKA-4546
> deleted records may be kept unexpectedly when leader changes while adding a
> new replica
> ---------------------------------------------------------------------------------------
>
> Key: KAFKA-14347
> URL: https://issues.apache.org/jira/browse/KAFKA-14347
> Project: Kafka
> Issue Type: Improvement
> Reporter: Vincent Jiang
> Priority: Major
>
> Consider that in a compacted topic, a regular record _k1=v1_ is deleted by a
> later tombstone record {_}k1=null{_}{_}.{_} And imagine that somehow __ log
> compaction is making different progress on the three replicas, {_}r1{_}, _r2_
> and _r3:_
> _-_ on replica {_}r1{_}, log compaction has not cleaned _k1=v1_ or _k1=null_
> yet.
> - on replica {_}r2{_}, log compaction cleaned and removed both _k1=v1_ and
> _k1=null._
> In this case, following sequence can cause record _k1=v1_ being kept
> unexpectedly:
> 1. Replica _r3_ is re-assigned to a different node and starts to replicate
> data from leader.
> 2. At the beginning, _r1_ is the leader, so _r3_ replicates record _k1=v1_
> from {_}r1{_}.
> 3. Before _k1=null_ is replicated from {_}r1{_}, leader changes to {_}r2{_}.
> 4. _r3_ replicates data from {_}r2{_}. Because _k1=null_ record has been
> cleaned in {_}r2{_}, it will not be replicated.
> As a result, _r3_ has record _k1=v1_ but not {_}k1=null{_}.
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