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https://issues.apache.org/jira/browse/HDFS-15477?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Tsz-wo Sze updated HDFS-15477:
------------------------------
    Description: 
Snapshot deletion has caused a few bugs earlier such as HDFS-13101 and 
HDFS-15313.  In this JIRA, we propose enforcing in-order snapshot deletion -- 
only the earliest snapshot is actually deleted from the file system.  The other 
snapshots are only marked as deleted.  They will be actually deleted from the 
file system until all the earlier snapshots are deleted.

The reason of enforcing in-order snapshot deletion is based on the observation 
that the logic of deleting the earliest snapshot is much simpler since the 
prior snapshot does not exist.  All the previous bugs are caused by removing 
inodes from the prior snapshots.

One drawback of in-order snapshot deletion is that the non-earliest snapshots 
are only marked as deleted but not actually deleted.  The resources are not yet 
released.

  was:
Snapshot deletion has caused a few bugs earlier such as HDFS-13101 and 
HDFS-15313.  In this JIRA, we propose enforcing in-order snapshot deletion -- 
only the earliest snapshot is actually deleted from the file system.  The other 
snapshots are only marked as deleted.  They will be actually deleted from the 
file system until all the earlier snapshots are deleted.




> Enforce in-order snapshot deletion
> ----------------------------------
>
>                 Key: HDFS-15477
>                 URL: https://issues.apache.org/jira/browse/HDFS-15477
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>          Components: snapshots
>            Reporter: Tsz-wo Sze
>            Assignee: Tsz-wo Sze
>            Priority: Major
>
> Snapshot deletion has caused a few bugs earlier such as HDFS-13101 and 
> HDFS-15313.  In this JIRA, we propose enforcing in-order snapshot deletion -- 
> only the earliest snapshot is actually deleted from the file system.  The 
> other snapshots are only marked as deleted.  They will be actually deleted 
> from the file system until all the earlier snapshots are deleted.
> The reason of enforcing in-order snapshot deletion is based on the 
> observation that the logic of deleting the earliest snapshot is much simpler 
> since the prior snapshot does not exist.  All the previous bugs are caused by 
> removing inodes from the prior snapshots.
> One drawback of in-order snapshot deletion is that the non-earliest snapshots 
> are only marked as deleted but not actually deleted.  The resources are not 
> yet released.



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