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From "stack (Commented) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-4811) Support reverse Scan
Date Tue, 22 Nov 2011 20:52:40 GMT

    [ https://issues.apache.org/jira/browse/HBASE-4811?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13155426#comment-13155426
] 

stack commented on HBASE-4811:
------------------------------

bq. Is there a fundamental reason that HBase only supports forward Scan?

Yes.  All the data is sorted in one direction only and all Scan objects are written to go
in the data's 'natural' direction.  There is no native support for going backwards whether
its reading from files 'backwards' or getting a view on our MemStore that gives a reverse-sort-view.

To make it work, you'd have to write a bunch of code and you'd be always going against the
grain.

It used to come up the odd time in the early days but versions on the above args would usually
quiet them.

If you need more detail, ask.
                
> 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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