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