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Date: Wed, 20 May 2009 12:12:45 -0700 (PDT)
From: "Jun Rao (JIRA)" <jira@apache.org>
To: cassandra-commits@incubator.apache.org
Subject: [jira] Commented: (CASSANDRA-172) A improved and more general
 version of get_slice
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    [ https://issues.apache.org/jira/browse/CASSANDRA-172?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12711300#action_12711300 ] 

Jun Rao commented on CASSANDRA-172:
-----------------------------------

The code you added doesn't work either. Suppose you have following:
insert (col1, val1, 1)
flush
delete(col1, 2)

and version 1 is iterated first, liveColumns is 1, which is incorrect.

In general, I don't think that you can write any code that works correctly by just increasing liveColumn. This is because you could see an obsolete version first and need be prepared to take it back later. You can fix the problem by having logic for both increasing and decreasing liveColumn. Then, the code is no longer much simpler than the my version. 


> A improved and more general version of get_slice
> ------------------------------------------------
>
>                 Key: CASSANDRA-172
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-172
>             Project: Cassandra
>          Issue Type: New Feature
>            Reporter: Jun Rao
>            Assignee: Jun Rao
>             Fix For: 0.4
>
>         Attachments: 172-addendum-SF.patch, 172-addendum.patch, get_slice_from.patchv1, get_slice_from.patchv2, get_slice_from.patchv3
>
>
> Today, get_slice has to scan through all columns in every memtable and sstable to get a slice of columns. This becomes inefficient when the number of columns in a row is large. We need a more efficient API.

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