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From "Feng Honghua (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-10241) implement mvcc-consistent scanners (across recovery)
Date Sun, 29 Dec 2013 03:34:53 GMT

    [ https://issues.apache.org/jira/browse/HBASE-10241?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13858234#comment-13858234

Feng Honghua commented on HBASE-10241:

I also encountered this issue when implementing JIRA-8721, the fix for "deletes can mask puts
that happen after the delete", and already persisted mvcc in WAL, and then they can be used
to recover region's correct mvcc during re-opening. Anyone who has interest can refer it :-)

Seems setting mvcc (per hfile) to zero for (minor, arguably) performance benefit can't offset
the correctness penalty it brings. Persisting mvcc and survive them across regionservers is
a matter of semantic correctness, seems most related issues can be resolved by making this
correct, combining mvcc and seqid is not as critical as this correcting.

> 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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