Jingcheng Du commented on HBASE-16841:

Thanks [~te...@apache.org], sure, let me try.

> Data loss in MOB files after cloning a snapshot and deleting that snapshot
> --------------------------------------------------------------------------
>                 Key: HBASE-16841
>                 URL: https://issues.apache.org/jira/browse/HBASE-16841
>             Project: HBase
>          Issue Type: Bug
>          Components: mob, snapshots
>            Reporter: Jingcheng Du
>            Assignee: Jingcheng Du
>         Attachments: HBASE-16841.patch
> Running the following steps will probably lose MOB data when working with 
> snapshots.
> 1. Create a mob-enabled table by running create 't1', {NAME => 'f1', IS_MOB 
> => true, MOB_THRESHOLD => 0}.
> 2. Put millions of data.
> 3. Run {{snapshot 't1','t1_snapshot'}} to take a snapshot for this table t1.
> 4. Run {{clone_snapshot 't1_snapshot','t1_cloned'}} to clone this snapshot.
> 5. Run {{delete_snapshot 't1_snapshot'}} to delete this snapshot.
> 6. Run {{disable 't1'}} and {{delete 't1'}} to delete the table.
> 7. Now go to the archive directory of t1, the number of .link directories is 
> different from the number of hfiles which means some data will be lost after 
> the hfile cleaner runs.
> This is because, when taking a snapshot on a enabled mob table, each region 
> flushes itself and takes a snapshot, and the mob snapshot is taken only if 
> the current region is first region of the table. At that time, the flushing 
> of some regions might not be finished, and some mob files are not flushed to 
> disk yet. Eventually some mob files are not recorded in the snapshot manifest.
> To solve this, we need to take the mob snapshot at last after the snapshots 
> on all the online and offline regions are finished in 
> {{EnabledTableSnapshotHandler}}.

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