[jira] [Commented] (KAFKA-14139) Replaced disk can lead to loss of committed data even with non-empty ISR

["Alexandre Dupriez (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/KAFKA-14139?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17682944#comment-17682944 ] 

Alexandre Dupriez commented on KAFKA-14139:
-------------------------------------------

Hi Calvin, yes, sure, I assigned the JIRA to you. 

> Replaced disk can lead to loss of committed data even with non-empty ISR
> ------------------------------------------------------------------------
>
>                 Key: KAFKA-14139
>                 URL: https://issues.apache.org/jira/browse/KAFKA-14139
>             Project: Kafka
>          Issue Type: Bug
>            Reporter: Jason Gustafson
>            Assignee: Calvin Liu
>            Priority: Major
>             Fix For: 3.5.0
>
>
> We have been thinking about disk failure cases recently. Suppose that a disk has failed and the user needs to restart the disk from an empty state. The concern is whether this can lead to the unnecessary loss of committed data.
> For normal topic partitions, removal from the ISR during controlled shutdown buys us some protection. After the replica is restarted, it must prove its state to the leader before it can be added back to the ISR. And it cannot become a leader until it does so.
> An obvious exception to this is when the replica is the last member in the ISR. In this case, the disk failure itself has compromised the committed data, so some amount of loss must be expected.
> We have been considering other scenarios in which the loss of one disk can lead to data loss even when there are replicas remaining which have all of the committed entries. One such scenario is this:
> Suppose we have a partition with two replicas: A and B. Initially A is the leader and it is the only member of the ISR.
>  # Broker B catches up to A, so A attempts to send an AlterPartition request to the controller to add B into the ISR.
>  # Before the AlterPartition request is received, replica B has a hard failure.
>  # The current controller successfully fences broker B. It takes no action on this partition since B is already out of the ISR.
>  # Before the controller receives the AlterPartition request to add B, it also fails.
>  # While the new controller is initializing, suppose that replica B finishes startup, but the disk has been replaced (all of the previous state has been lost).
>  # The new controller sees the registration from broker B first.
>  # Finally, the AlterPartition from A arrives which adds B back into the ISR even though it has an empty log.
> (Credit for coming up with this scenario goes to [~junrao] .)
> I tested this in KRaft and confirmed that this sequence is possible (even if perhaps unlikely). There are a few ways we could have potentially detected the issue. First, perhaps the leader should have bumped the leader epoch on all partitions when B was fenced. Then the inflight AlterPartition would be doomed no matter when it arrived.
> Alternatively, we could have relied on the broker epoch to distinguish the dead broker's state from that of the restarted broker. This could be done by including the broker epoch in both the `Fetch` request and in `AlterPartition`.
> Finally, perhaps even normal kafka replication should be using a unique identifier for each disk so that we can reliably detect when it has changed. For example, something like what was proposed for the metadata quorum here: [https://cwiki.apache.org/confluence/display/KAFKA/KIP-853%3A+KRaft+Voter+Changes].



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