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From "Enis Soztutar (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-10241) implement mvcc-consistent scanners (across recovery)
Date Mon, 06 Jan 2014 22:37:53 GMT

    [ https://issues.apache.org/jira/browse/HBASE-10241?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13863531#comment-13863531
] 

Enis Soztutar commented on HBASE-10241:
---------------------------------------

We need to fix this for a couple of different reasons: 
 - Fixing scanner consistency with multi-row transactions (see HBASE-9797) 
 - Adding cell-based scanners, and streaming scans 
 - Adding single-row scanners. 
 - Consistent scanners with region replicas in case replicas are mostly up to date (HBASE-10070)


What is the plan here? I think we should do subtasks 1 and 3 regardless of HBASE-8763. But
it seems that if we do HBASE-8763 first, it will be much cleaner and we won't need subtask
2 at all. 


> implement mvcc-consistent scanners (across recovery)
> ----------------------------------------------------
>
>                 Key: HBASE-10241
>                 URL: https://issues.apache.org/jira/browse/HBASE-10241
>             Project: HBase
>          Issue Type: New Feature
>          Components: HFile, regionserver, Scanners
>    Affects Versions: 0.99.0
>            Reporter: Sergey Shelukhin
>            Assignee: Sergey Shelukhin
>         Attachments: Consistent scanners.pdf
>
>
> Scanners currently use mvcc for consistency. However, mvcc is lost on server restart,
or even a region move. This JIRA is to enable the scanners to transfer mvcc (or seqId, or
some other number, see HBASE-8763) between servers. First, client scanner needs to get and
store the readpoint. Second, mvcc needs to be preserved in WAL. Third, the mvcc needs to be
stored in store files per KV and discarded when not needed.



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