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https://issues.apache.org/jira/browse/DERBY-884?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13030737#comment-13030737
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Dag H. Wanvik commented on DERBY-884:
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2) sounds like a good solution to me. I'd prefer that over 1) if it doesn't get
too complex, I think. I agree it might be too
costly to impose locking the previous row for inserts in the more common
non-serializable modes..better pay the complexity in the backwards scan.
> allow and use backward scans on indexes.
> ----------------------------------------
>
> Key: DERBY-884
> URL: https://issues.apache.org/jira/browse/DERBY-884
> Project: Derby
> Issue Type: Improvement
> Components: SQL, Store
> Affects Versions: 10.1.3.1
> Reporter: Mike Matrigali
> Priority: Minor
>
> Improve the access interface to support backward scans, currently only
> forward scans are supported.
> Improve the btree implementation to support backward scans. The structure
> could support this, the work just has not been done. With
> row level locking, concurrent tree splitting, and current assumptions
> throughout the access method that scans go top/down, left to right the
> work to do a backward scan is harder than doing a forward scan. Also
> once the store portion is done, there would be necessary changes to:
> optimizer, execution engine, and scan interface to allow the backward
> scan. This would be a hard first project.
> Improve the optimizer to understand derby indexes now support backward scans.
> Improve the execution engine to use the new backward scan interfaces to
> execute backward scans.
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