[HBASE-28720] Merge repairs always fail to restore the BackupSystemTable snapshot

• Type: Bug
• Status: Open
• Priority: Minor
• Resolution: Unresolved
• Affects Version/s: 2.6.0, 3.0.0, 4.0.0-alpha-1
• Component/s: backup&restore
• Assignee: Unassigned
• Reporter: Dieter De Paepe
• Created: 09/Jul/24 15:39
• Updated: 10/Jul/24 09:35

Description

In `BackupCommands.RepairCommand#execute`, the following code block is present:

repairFailedBackupDeletionIfAny(conn, sysTable);
repairFailedBackupMergeIfAny(conn, sysTable); 

Both of these methods can be sketched as:

if (there are no unresolved merges/deletes) {
    BackupSystemTable.deleteSnapshot(conn);
} else {
    BackupSystemTable.restoreFromSnapshot(conn);
    retry merge/delete
}

In case of failed merges, there will be no unresolved deletes, hence the BackupSystemTable snapshot will be deleted. As a result, the restore for the merges will always fail.

Currently unsure what the risks of this are, haven't explored the merge code yet.

Update: it looks like the merge code doesn't create a BackupSystemTable snapshot. So the restore/delete snapshot for the merge method is pointless.