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https://issues.apache.org/jira/browse/HUDI-1649?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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sivabalan narayanan updated HUDI-1649:
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Labels: sev:high user-support-issues (was: )
> Bugs with Metadata Table in 0.7 release
> ---------------------------------------
>
> Key: HUDI-1649
> URL: https://issues.apache.org/jira/browse/HUDI-1649
> Project: Apache Hudi
> Issue Type: Sub-task
> Affects Versions: 0.9.0
> Reporter: Prashant Wason
> Assignee: Prashant Wason
> Priority: Critical
> Labels: sev:high, user-support-issues
> Fix For: 0.9.0
>
>
> We have discovered the following issues while using the Metadata Table code
> in production:
>
> *Issue 1: Automatic rollbacks during commit get a timestamp which is out of
> order*
> Suppose commit C1 failed. The next commit will try to rollback C1
> automatically. This will create the following two instances C2.commit and
> R3.rollback. Hence, the rollback will have a timestamp > the commit which
> occurs after it.
> This is because of how the code is implemented in
> AbstractHoodieWriteClient.startCommitWithTime() where the timestamp of the
> next commit is chosen before the timestamp of the rollback instant.
>
> *Issue 2: Syncing of rollbacks is not working*
> Due to the above HUDI issue, syncing of rollbacks in Metadata Table does not
> work correctly.
> Assume the timeline as follows:
> Dataset Timeline: C1 C2. C3
> Metadata Timeline: DC1 DC2. (dc=delta-commit)
>
> Suppose the next commit C4 fails. When C5 is attempted, C4 will be
> automatically tolled back. Due to the issue #1, the timelines will become as
> follows:
> Dataset Timeline: C1 C2. C3. C5 R6
> Metadata Timeline: DC1 DC2
> Now if the Metadata Table is synced (AbstractHoodieWriteClient.postCommit),
> the code will end up processing C5 first and then R6 which will mean that the
> file rolled back in R6 will be committed to the metadata table as deleted
> files. There is logic within
> HoodieTableMetadataUtils.processRollbackMetadata() to ignore R6 in this
> scenario but it does not work because of the issue #1.
>
> *Issue #3: Rollback instants are deleted inline*
> Current rollback code deleted older instants inline. The delete logic keeps
> oldest ten instants (hardcoded) and removes all more-recent rollback
> instants. Furthermore, the deletion ONLY deletes the rollback.complete and
> does not remove the corresponding rollback.inflight files.
> Hence, will many rollbacks the following timeline is possible
> Timeline: C1. C2 C3 C4. R5.inflight C5 C6 C7 ...
> (there are 9 previous rollback instants to R5).
>
> *Issue #4: Metadata Table reader does not show correct view of the metadata*
> Assume the timeline is as in Issue #3 with a leftover rollback.inflight
> instant. Also assume that the metadata table is synced only till C4. The
> MetadataTableWriter will not sync any more instants to the Metadata Table
> since an incomplete instant is present next.
> The same sync logic is also used by the MetadataReader to perform the
> in-memory merge of timeline. Hence, the reader will also not consider C5, C6
> and C7 thereby providing an incorrect and older view of the FileSlices and
> FileGroups.
>
> Any future ingestion into this table MAY insert data into older versions of
> the FileSlices which will end up being a data loss when queried.
>
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