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From "Jingcheng Du (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-18693) adding an option to restore_snapshot to move mob files from archive dir to working dir
Date Tue, 29 Aug 2017 06:03:00 GMT

    [ https://issues.apache.org/jira/browse/HBASE-18693?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16144792#comment-16144792
] 

Jingcheng Du commented on HBASE-18693:
--------------------------------------

Thanks [~huangxiangang].
The restore operations should be a fast one, moving data in such an operation is not proper
I think.
Could we just skip the hfile link, or just compact them no matter what size it is in the compaction?
How about this?

> adding an option to restore_snapshot to move mob files from archive dir to working dir
> --------------------------------------------------------------------------------------
>
>                 Key: HBASE-18693
>                 URL: https://issues.apache.org/jira/browse/HBASE-18693
>             Project: HBase
>          Issue Type: Improvement
>          Components: mob
>    Affects Versions: 2.0.0-alpha-2
>            Reporter: huaxiang sun
>            Assignee: huaxiang sun
>
> Today, there is a single mob region where mob files for all user regions are saved. There
could be many files (one million) in a single mob directory. When one mob table is restored
or cloned from snapshot, links are created for these mob files. This creates a scaling issue
for mob compaction. In mob compaction's select() logic, for each hFileLink, it needs to call
NN's getFileStatus() to get the size of the linked hfile. Assume that one such call takes
20ms, 20ms * 1000000 = 6 hours. 
> To avoid this overhead, we want to add an option so that restore_snapshot can move mob
files from archive dir to working dir. clone_snapshot is more complicated as it can clone
a snapshot to a different table so moving that can destroy the snapshot. No option will be
added for clone_snapshot.



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