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From "Pranav Khaitan (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HBASE-2856) TestAcidGuarantee broken on trunk
Date Fri, 20 Aug 2010 00:28:16 GMT

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Pranav Khaitan commented on HBASE-2856:
---------------------------------------

I guess we could fix this by not updating the scanners after a flush. Currently, after every
flush we are notifying the scanners (called as observers) so that they update their heap.
If we do not notify them about the flush, the scanner wouldn't encounter any inconsistencies.
This should solve the specific problem you discussed above where flushing results in inconsistency.
This seems like an easy change and maintains correctness. The only drawback is that we are
holding some memstore keys for a little longer which doesn't seem too big of a problem.

> 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: ryan rawson
>            Priority: Blocker
>             Fix For: 0.90.0
>
>
> 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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