* [HUDI-2119] Ensure the rolled-back instance was previously synced to the Metadata Table when syncing a Rollback Instant.
If the rolled-back instant was synced to the Metadata Table, a corresponding deltacommit with the same timestamp should have been created on the Metadata Table timeline. To ensure we can always perfomr this check, the Metadata Table instants should not be archived until their corresponding instants are present in the dataset timeline. But ensuring this requires a large number of instants to be kept on the metadata table.
In this change, the metadata table will keep atleast the number of instants that the main dataset is keeping. If the instant being rolled back was before the metadata table timeline, the code will throw an exception and the metadata table will have to be re-bootstrapped. This should be a very rare occurance and should occur only when the dataset is being repaired by rolling back multiple commits or restoring to an much older time.
* Fixed checkstyle
* Improvements from review comments.
Fixed checkstyle
Replaced explicit null check with Option.ofNullable
Removed redundant function getSynedInstantTime
* Renamed getSyncedInstantTime and getSyncedInstantTimeForReader.
Sync is confusing so renamed to getUpdateTime() and getReaderTime().
* Removed getReaderTime which is only for testing as the same method can be accessed during testing differently without making it part of the public interface.
* Fix compilation error
* Reverting changes to HoodieMetadataFileSystemView
Co-authored-by: Vinoth Chandar <vinoth@apache.org>
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