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From "stack (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-6200) KeyComparator.compareWithoutRow can be wrong when families have the same prefix
Date Fri, 22 Jun 2012 15:56:43 GMT

    [ https://issues.apache.org/jira/browse/HBASE-6200?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13399401#comment-13399401
] 

stack commented on HBASE-6200:
------------------------------

Patch looks good.  I'm not sure I'm clear what commonPrefix is... how its used.  For example,
what is going on here:

{code}
+    // 'fami:qf1' < 'fami:qf2' With commonPrefix + 4 bytes prefix.
+    assertKVLessWithoutRow(c, commonPrefix + 4, kv0_1, kv0_2);
+    // 'fami:qf1' < 'fami:qf2' With commonPrefix + 6 bytes prefix.
+    assertKVLessWithoutRow(c, commonPrefix + 6, kv0_1, kv0_2);
{code}

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.

This stuff is hard to follow at the best of times so while it looks like this is fixed with
this patch -- thanks for doing it -- any chance of a bit more explaination either w/ comments
or improved javadoc.

Otherwise, patch looks great.  Tests are nice.
                
> 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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