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Date: Tue, 26 Jun 2012 01:42:44 +0000 (UTC)
From: "Jieshan Bean (JIRA)" <jira@apache.org>
To: issues@hbase.apache.org
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Subject: [jira] [Commented] (HBASE-6200) KeyComparator.compareWithoutRow can
 be wrong when families have the same prefix
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    [ https://issues.apache.org/jira/browse/HBASE-6200?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13401094#comment-13401094 ] 

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

bq.So if I read that right 1.000.000 KV compares take 100ms without the patch and 121ms with the patch. 
1,000,000 times called the below method(Will compare 2 times in each call), to be exact:
{noformat}
  private void assertKVLessWithoutRow(KeyValue.KeyComparator c, int common, KeyValue less,
      KeyValue greater) {
    int cmp = c.compareIgnoringPrefix(common, less.getBuffer(), less.getOffset()
        + KeyValue.ROW_OFFSET, less.getKeyLength(), greater.getBuffer(),
        greater.getOffset() + KeyValue.ROW_OFFSET, greater.getKeyLength());
    assertTrue(cmp < 0);
    cmp = c.compareIgnoringPrefix(common, greater.getBuffer(), greater.getOffset()
        + KeyValue.ROW_OFFSET, greater.getKeyLength(), less.getBuffer(),
        less.getOffset() + KeyValue.ROW_OFFSET, less.getKeyLength());
    assertTrue(cmp > 0);
  }
{noformat}

Thanks, Lars & Ted.
                
> 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-v2.patch, HBASE-6200-90.patch, HBASE-6200-92-v2.patch, HBASE-6200-92.patch, HBASE-6200-94-v2.patch, HBASE-6200-94.patch, HBASE-6200-trunk-v2.patch, HBASE-6200-trunk.patch, PerformanceTestCase-6200-94.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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