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From "Dag H. Wanvik (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (DERBY-884) allow and use backward scans on indexes.
Date Mon, 09 May 2011 13:51:03 GMT

    [ https://issues.apache.org/jira/browse/DERBY-884?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13030737#comment-13030737
] 

Dag H. Wanvik commented on DERBY-884:
-------------------------------------

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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