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From "Sergey Shelukhin (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-10241) implement mvcc-consistent scanners (across recovery)
Date Mon, 06 Jan 2014 23:42:50 GMT

    [ https://issues.apache.org/jira/browse/HBASE-10241?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13863654#comment-13863654
] 

Sergey Shelukhin commented on HBASE-10241:
------------------------------------------

That would be PITA from backward compat perspective - we'd both add a field, requiring HFileFormat
v4 (don't really want tag overhead for this), and presumably (tags or not) remove the old
magic mechanism

> 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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