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Date: Tue, 6 Jul 2010 16:21:52 -0400 (EDT)
From: "Jonathan Ellis (JIRA)" <jira@apache.org>
To: commits@cassandra.apache.org
Subject: [jira] Commented: (CASSANDRA-1042) ColumnFamilyRecordReader returns
 duplicate rows
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    [ https://issues.apache.org/jira/browse/CASSANDRA-1042?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12885670#action_12885670 ] 

Jonathan Ellis commented on CASSANDRA-1042:
-------------------------------------------

the "correct" order when tokens are involved is ring order

(when start_key is used instead of start_token, you can't have a wrapping range so it should be moot)

> ColumnFamilyRecordReader returns duplicate rows
> -----------------------------------------------
>
>                 Key: CASSANDRA-1042
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-1042
>             Project: Cassandra
>          Issue Type: Bug
>          Components: Hadoop
>    Affects Versions: 0.6
>            Reporter: Joost Ouwerkerk
>            Assignee: Jeremy Hanna
>             Fix For: 0.6.4
>
>         Attachments: 1042-0_6.txt, Cassandra-1042-0_6-branch.patch.txt, CASSANDRA-1042-trunk.patch.txt, cassandra.tar.gz, duplicate_keys.rtf
>
>
> There's a bug in ColumnFamilyRecordReader that appears when processing a single split (which happens in most tests that have small number of rows), and potentially in other cases.  When the start and end tokens of the split are equal, duplicate rows can be returned.
> Example with 5 rows:
> token (start and end) = 53193025635115934196771903670925341736
> Tokens returned by first get_range_slices iteration (all 5 rows):
>  16955237001963240173058271559858726497
>  40670782773005619916245995581909898190
>  99079589977253916124855502156832923443
>  144992942750327304334463589818972416113
>  166860289390734216023086131251507064403
> Tokens returned by next iteration (first token is last token from
> previous, end token is unchanged)
>  16955237001963240173058271559858726497
>  40670782773005619916245995581909898190
> Tokens returned by final iteration  (first token is last token from
> previous, end token is unchanged)
>  [] (empty)
> In this example, the mapper has processed 7 rows in total, 2 of which
> were duplicates.

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