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From "ryan rawson (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HBASE-2856) TestAcidGuarantee broken on trunk
Date Tue, 07 Dec 2010 00:24:11 GMT

    [ https://issues.apache.org/jira/browse/HBASE-2856?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12968505#action_12968505
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ryan rawson commented on HBASE-2856:
------------------------------------

I think we can use HLog sequenceID as the "insertion sequence ID".  

This is how it will work:

- HLog append happens, resulting in sequence ID  "X"
- Start memstoreInsert, but instead of using what is provided, use X instead.
- Do the usual, stamping KVs with X
- Commit and push read point forward to X when done.

Successive "X" values will be increasing in value.  One thing we will need to do is initialize
"RWCC" read point to the largest HLog sequenceID on Region open (before region can take any
edits).  



> TestAcidGuarantee broken on trunk 
> ----------------------------------
>
>                 Key: HBASE-2856
>                 URL: https://issues.apache.org/jira/browse/HBASE-2856
>             Project: HBase
>          Issue Type: Bug
>    Affects Versions: 0.89.20100621
>            Reporter: ryan rawson
>            Assignee: stack
>            Priority: Blocker
>             Fix For: 0.92.0
>
>
> TestAcidGuarantee has a test whereby it attempts to read a number of columns from a row,
and every so often the first column of N is different, when it should be the same.  This is
a bug deep inside the scanner whereby the first peek() of a row is done at time T then the
rest of the read is done at T+1 after a flush, thus the memstoreTS data is lost, and previously
'uncommitted' data becomes committed and flushed to disk.
> One possible solution is to introduce the memstoreTS (or similarly equivalent value)
to the HFile thus allowing us to preserve read consistency past flushes.  Another solution
involves fixing the scanners so that peek() is not destructive (and thus might return different
things at different times alas).

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