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https://issues.apache.org/jira/browse/HBASE-7342?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13531275#comment-13531275
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stack commented on HBASE-7342:
------------------------------
+1 on fix. I'd not add the test. Its overkill running a cluster to test a
array math problem.
> Split operation without split key incorrectly finds the middle key in
> off-by-one error
> --------------------------------------------------------------------------------------
>
> Key: HBASE-7342
> URL: https://issues.apache.org/jira/browse/HBASE-7342
> Project: HBase
> Issue Type: Bug
> Components: HFile, io
> Affects Versions: 0.94.1, 0.94.2, 0.94.3, 0.96.0
> Reporter: Aleksandr Shulman
> Assignee: Aleksandr Shulman
> Priority: Minor
> Fix For: 0.96.0, 0.94.4
>
> Attachments: HBASE-7342-v1.patch, HBASE-7342-v2.patch
>
>
> I took a deeper look into issues I was having using region splitting when
> specifying a region (but not a key for splitting).
> The midkey calculation is off by one and when there are 2 rows, will pick the
> 0th one. This causes the firstkey to be the same as midkey and the split will
> fail. Removing the -1 causes it work correctly, as per the test I've added.
> Looking into the code here is what goes on:
> 1. Split takes the largest storefile
> 2. It puts all the keys into a 2-dimensional array called blockKeys[][]. Key
> i resides as blockKeys[i]
> 3. Getting the middle root-level index should yield the key in the middle of
> the storefile
> 4. In step 3, we see that there is a possible erroneous (-1) to adjust for
> the 0-offset indexing.
> 5. In a result with where there are only 2 blockKeys, this yields the 0th
> block key.
> 6. Unfortunately, this is the same block key that 'firstKey' will be.
> 7. This yields the result in HStore.java:1873 ("cannot split because midkey
> is the same as first or last row")
> 8. Removing the -1 solves the problem (in this case).
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