huaxiang sun created HBASE-18693:
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Summary: 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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