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From "John Carrino (Commented) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-4811) Support reverse Scan
Date Wed, 23 Nov 2011 16:55:39 GMT

    [ https://issues.apache.org/jira/browse/HBASE-4811?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13155961#comment-13155961
] 

John Carrino commented on HBASE-4811:
-------------------------------------

Digging a littler deeper it appears that this was already planned when the V2 HFile format
was written.  In the header of a block is the offset of the previous block of the same type.
 I think this is currently used to support efficient lookups when seeking to a location, but
could also be used easily for reverse scan.
                
> Support reverse Scan
> --------------------
>
>                 Key: HBASE-4811
>                 URL: https://issues.apache.org/jira/browse/HBASE-4811
>             Project: HBase
>          Issue Type: Improvement
>          Components: client
>    Affects Versions: 0.20.6
>            Reporter: John Carrino
>
> All the documentation I find about HBase says that if you want forward and reverse scans
you should just build 2 tables and one be ascending and one descending.  Is there a fundamental
reason that HBase only supports forward Scan?  It seems like a lot of extra space overhead
and coding overhead (to keep them in sync) to support 2 tables.  
> I am assuming this has been discussed before, but I can't find the discussions anywhere
about it or why it would be infeasible.

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