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https://issues.apache.org/jira/browse/HBASE-18693?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16144813#comment-16144813
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huaxiang sun commented on HBASE-18693:
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Thanks [~jingcheng.du]. hdfs move() is a very light operation. I browsed the
source code and also looked at
https://stackoverflow.com/questions/34512596/how-does-hdfs-mv-command-work. As
far as I understand, it only involves name node and no real data operation is
performed. Skip hFileLink may not work as some mob hFileLinks need to be
compacted to reduce file number in the directory. If these HFileLinks are
compacted always, this will cause lots of unnecessary IOs as mob files will be
created. Please share your thoughts, thanks.
> 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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