[jira] [Commented] (HBASE-4811) Support reverse Scan

["stack (Commented) (JIRA)" <ji...@apache.org>]

    [ 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:
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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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