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From "Jieshan Bean (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-6200) KeyComparator.compareWithoutRow can be wrong when families have the same prefix
Date Mon, 25 Jun 2012 01:50:42 GMT

    [ https://issues.apache.org/jira/browse/HBASE-6200?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13400248#comment-13400248
] 

Jieshan Bean commented on HBASE-6200:
-------------------------------------

bq.Patch looks good. I'm not sure I'm clear what commonPrefix is... how its used. For example,
what is going on here:
bq.We move from commonPrefix+4 to commonPrefix+6. Is this commonPrefix w/i the row only? Or
is it row+? It seems its row? Its not clear from the javadoc nor as I walk through.

Sorry for the confusion. I will add more comments to explain this:). I will refresh the patches
today.
bq.Probably we should use variable of same name instead of commonPrefix.
				  
Ya...I should use "commonLength":)

bq.Also with this change, since KVs are compared extremely frequently we should performance
test this.

Lars, do you have any suggestions on this?:)
                
> KeyComparator.compareWithoutRow can be wrong when families have the same prefix
> -------------------------------------------------------------------------------
>
>                 Key: HBASE-6200
>                 URL: https://issues.apache.org/jira/browse/HBASE-6200
>             Project: HBase
>          Issue Type: Bug
>    Affects Versions: 0.90.6, 0.92.1, 0.94.0
>            Reporter: Jean-Daniel Cryans
>            Assignee: Jieshan Bean
>            Priority: Blocker
>             Fix For: 0.90.7, 0.92.2, 0.96.0, 0.94.1
>
>         Attachments: 6200-trunk-v2.patch, HBASE-6200-90.patch, HBASE-6200-92.patch, HBASE-6200-94.patch,
HBASE-6200-trunk-v2.patch, HBASE-6200-trunk.patch
>
>
> As reported by Desert Rose on IRC and on the ML, {{Result}} has a weird behavior when
some families share the same prefix. He posted a link to his code to show how it fails, http://pastebin.com/7TBA1XGh
> Basically {{KeyComparator.compareWithoutRow}} doesn't differentiate families and qualifiers
so "f:a" is said to be bigger than "f1:", which is false. Then what happens is that the KVs
are returned in the right order from the RS but then doing {{Result.binarySearch}} it uses
{{KeyComparator.compareWithoutRow}} which has a different sorting so the end result is undetermined.
> I added some debug and I can see that the data is returned in the right order but {{Arrays.binarySearch}}
returned the wrong KV, which is then verified agains the passed family and qualifier which
fails so null is returned.
> I don't know how frequent it is for users to have families with the same prefix, but
those that do have that and that use those families at the same time will have big correctness
issues. This is why I mark this as a blocker.

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