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https://issues.apache.org/jira/browse/HUDI-3604?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Ethan Guo closed HUDI-3604.
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Resolution: Fixed
> Missing to apply rollback commits to Metadata table if rollback failed mid-way
> ------------------------------------------------------------------------------
>
> Key: HUDI-3604
> URL: https://issues.apache.org/jira/browse/HUDI-3604
> Project: Apache Hudi
> Issue Type: Bug
> Components: metadata
> Reporter: sivabalan narayanan
> Assignee: Ethan Guo
> Priority: Blocker
> Labels: pull-request-available
> Fix For: 0.11.0
>
>
> C1, C2, C3. C4 (RB_C1) in progress.
> When C4 (i.e. RB of C1 is triggered), after deleting data files, and after
> deleting the commits files in timeline (C1), let's say the process crashed
> (before applying to MDT).
> Even if the user restarts the pipeline, there won't be any pending failed
> commits(i.e. C1) to rollback and new commit will continue. w/o worrying about
> C4. But metadata table will miss out this rollback commit.
>
> Proposal:
> We need two fixes atleast:
> a. We should clean the C1 commit files from data table timeline only after
> applying the rollback commit to MDT. This way we will ensure no commit files
> in data table will be cleaned up before applying the rollback to MDT.
> b. Whenever we check for failed commits to rollback, we should also check for
> any dangling rollback to be re-attempted. This again needs some fixes in
> rollback executor as well. since chances that the commit to rollback may not
> exist in data table timeline at all. but we need to re-attempt the rollback
> and get it to completion(so that we let metadata make progress wrt
> compactions). It's not easy to detect a pending rollback from a dangling
> rollback. So, can't think of ways to detect dangling rollback just by looking
> at data table active timeline. hence had to re-attempt any pending rollback
> instants and get it to completion.
>
> Dangling rollbacks:
> Following up on above eg:
> C1, C2, C3, C4(RB_C1) failed mid-way. But the crash happens after deleting
> the datafiles and deleting commit files in data timeline. So, lets say the
> process crashes as of now (before applying to MDT). If the user restarts the
> pipeline, hudi will check for partially failed commits to trigger rollback.
> But since C1 is deleted from the timeline by C4(RB_C1), rollback of C1 will
> not kick in. So, C4 i.e RB_C1 will just stay in the timeline forever since
> there is no other trigger that can take it to completion or delete it.
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