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From "ramkrishna.s.vasudevan (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-17177) Major compaction can break the region/row level atomic when scan even if we pass mvcc to client
Date Mon, 28 Nov 2016 05:31:58 GMT

    [ https://issues.apache.org/jira/browse/HBASE-17177?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15700974#comment-15700974
] 

ramkrishna.s.vasudevan commented on HBASE-17177:
------------------------------------------------

If a major compaction had already started and that time a region move happens then we can
still delay the major compaction of the region that got newly moved? 
May be we should complete the major compaction of other regions and then come back to this
so that overall there is no delay in completing major compaction. 

> Major compaction can break the region/row level atomic when scan even if we pass mvcc
to client
> -----------------------------------------------------------------------------------------------
>
>                 Key: HBASE-17177
>                 URL: https://issues.apache.org/jira/browse/HBASE-17177
>             Project: HBase
>          Issue Type: Sub-task
>          Components: scan
>            Reporter: Duo Zhang
>             Fix For: 2.0.0, 1.4.0
>
>
> We know that major compaction will actually delete the cells which are deleted by a delete
marker. In order to give a consistent view for a scan, we need to use a map to track the read
points for all scanners for a region, and the smallest one will be used for a compaction.
For all delete markers whose mvcc is greater than this value, we will not use it to delete
other cells.
> And the problem for a scan restart after region move is that, the new RS does not have
the information of the scanners opened at the old RS before the client sends scan requests
to the new RS which means the read points map is incomplete and the smallest read point maybe
greater than the correct value. So if a major compaction happens at that time, it may delete
some cells which should be kept.



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