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From "ryan rawson (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HBASE-2856) TestAcidGuarantee broken on trunk
Date Thu, 13 Jan 2011 01:13:47 GMT

    [ https://issues.apache.org/jira/browse/HBASE-2856?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12981063#action_12981063
] 

ryan rawson commented on HBASE-2856:
------------------------------------

if you use a per-CF sequence ID you can only have atomic properties on
at most a column family.  We use the transaction id to know which ones
were committed and which ones were not, and if it wasn't across all
the CFs, we would not have atomicity across all CFs which is what we
DO want.

even if we split flushes to happen on per-Store/CF basis, it would not
affect the acid guarantees we are trying to achieve with this patch.


> 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
>
>         Attachments: 2856-v2.txt, 2856-v3.txt, acid.txt
>
>
> 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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