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From "Jeffrey Zhong (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-8763) [BRAINSTORM] Combine MVCC and SeqId
Date Tue, 03 Dec 2013 03:57:35 GMT

    [ https://issues.apache.org/jira/browse/HBASE-8763?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13837300#comment-13837300
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Jeffrey Zhong commented on HBASE-8763:
--------------------------------------

I tried a small patch. Since we support SKIP_WAL model, the MVCC.writeQueue is still needed
to main the write order because there is no wal sync operation at all.  Also there are quite
a few test cases doesn't do appendNosync between mvcc.beginMemstoreInsert and mvcc.completeMemstoreInsert
so they are needed to be adjusted. So far I didn't find block issues but still need to verify
it thoroughly.

> [BRAINSTORM] Combine MVCC and SeqId
> -----------------------------------
>
>                 Key: HBASE-8763
>                 URL: https://issues.apache.org/jira/browse/HBASE-8763
>             Project: HBase
>          Issue Type: Improvement
>          Components: regionserver
>            Reporter: Enis Soztutar
>         Attachments: hbase-8763_wip1.patch
>
>
> HBASE-8701 and a lot of recent issues include good discussions about mvcc + seqId semantics.
It seems that having mvcc and the seqId complicates the comparator semantics a lot in regards
to flush + WAL replay + compactions + delete markers and out of order puts. 
> Thinking more about it I don't think we need a MVCC write number which is different than
the seqId. We can keep the MVCC semantics, read point and smallest read points intact, but
combine mvcc write number and seqId. This will allow cleaner semantics + implementation +
smaller data files. 
> We can do some brainstorming for 0.98. We still have to verify that this would be semantically
correct, it should be so by my current understanding.



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