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https://issues.apache.org/jira/browse/KAFKA-905?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Neha Narkhede resolved KAFKA-905.
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Resolution: Fixed
Thanks for v2, committed it to 0.8
> Logs can have same offsets causing recovery failure
> ---------------------------------------------------
>
> Key: KAFKA-905
> URL: https://issues.apache.org/jira/browse/KAFKA-905
> Project: Kafka
> Issue Type: Bug
> Affects Versions: 0.8
> Reporter: Sriram Subramanian
> Assignee: Sriram Subramanian
> Fix For: 0.8
>
> Attachments: KAFKA-905.patch, KAFKA-905.rtf, KAFKA-905-v2.patch
>
>
> Consider the following scenario -
> L F
> 1 m1,m2 1 m1,m2
> 3 m3,m4 3 m3,m4
> 5 m5,m6 5 m5,m6
> HW = 6 HW = 4
> Follower goes down and comes back up. Truncates its log to HW
> L F
> 1 m1,m2 1 m1,m2
> 3 m3,m4 3 m3,m4
> 5 m5,m6
> HW = 6 HW = 4
> Before follower catches up with the leader, leader goes down and follower
> becomes the leader. It then gets new messages
> F L
> 1 m1,m2 1 m1,m2
> 3 m3,m4 3 m3,m4
> 5 m5,m6 10 m5-m10
> HW=6 HW=4
> follower fetches from offset 7. Since offset 7 is within the compressed
> message 10 in the leader, the whole message chunk is sent to the follower
> F L
> 1 m1,m2 1 m1,m2
> 3 m3,m4 3 m3,m4
> 5 m5,m6 10 m5-m10
> 10 m5-m10
> HW=4 HW=10
> The follower logs now contain the same offsets. On recovery, re-indexing will
> fail due to repeated offsets.
> Possible ways to fix this -
> 1. The fetcher thread can do deep iteration instead of shallow iteration and
> drop the offsets that are less than the log end offset. This would however
> incur performance hit.
> 2. To optimize step 1, we could do the deep iteration till the logical offset
> of the fetched message set is greater than the log end offset of the follower
> log and then switch to shallow iteration.
> 3. On recovery we just truncate the active segment and refetch the data.
> All the above 3 steps are hacky. The right fix is to ensure we never corrupt
> the logs. We can incur data loss but should not compromise consistency. For
> 0.8, the easiest and simplest fix would be 3.
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