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https://issues.apache.org/jira/browse/HBASE-10241?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13857607#comment-13857607
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stack commented on HBASE-10241:
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+1 on it being on by default and config is only to turn it off if problematic.
On mvcc giving consistent view on region, that is unnecessary, right -- when
would we ever care about a consistent view across a region rather than just
across a row (other than the fact that row boundaries are only known after the
fact, after you have passed them out) -- so if that the case, we should make do
w/ the lesser scope if we can.
When I say cost, I mean the amount of extra checks and work the server will
have to do to enforce this consistency (the fancy dancing necessary enforcing
the period during which a scanner may come in post recover of a server -- will
we suspend compactions during this time or will compactions have a special flag
which says do not drop mvcc .... so no full compactions during this period --
and so on).
> 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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