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From "Duo Zhang (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 Fri, 02 Dec 2016 05:35:58 GMT

    [ https://issues.apache.org/jira/browse/HBASE-17177?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15714130#comment-15714130
] 

Duo Zhang commented on HBASE-17177:
-----------------------------------

{quote}
Not sure about NONE/ROW/REGION. Can we do REGION first, since mvcc is by region, and then
if needed do ROW and NONE.
{quote}

NONE/ROW/REGION is the lower bound, if there is no error then we will always have the REGION
level atomicity. The problem only happens when there is an error and we need to reopen a scanner.
We will try our best to keep the REGION level atomicity but as said above, we can not always
succeed. And if the bad things happen, then we will use the 'atomicity' option to determine
if we can go on or throw an exception to user.

Thanks.

> 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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