db-derby-dev mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From "Kathey Marsden (JIRA)" <derby-...@db.apache.org>
Subject [jira] Updated: (DERBY-642) SELECT MAX doesn't use indices optimally
Date Fri, 28 Jul 2006 23:59:18 GMT
     [ http://issues.apache.org/jira/browse/DERBY-642?page=all ]

Kathey Marsden updated DERBY-642:
---------------------------------

    Fix Version/s:     (was: 10.2.0.0)

removing from 10.2. see:
http://www.nabble.com/10.2-High-Value-Fix-Candidates-and-Fix-Version-Adjustments-tf2007999.html

> SELECT MAX doesn't use indices optimally
> ----------------------------------------
>
>                 Key: DERBY-642
>                 URL: http://issues.apache.org/jira/browse/DERBY-642
>             Project: Derby
>          Issue Type: Improvement
>          Components: Store, Performance
>    Affects Versions: 10.2.0.0
>            Reporter: Knut Anders Hatlen
>            Priority: Minor
>
> I tried running SELECT MAX on an indexed column in a big (8 GB)
> table. It took 12 minutes, which is about 12 minutes more than I
> expected.
> After a bit of investigation, I found out that a full index scan was
> performed because all the rows referenced from the rightmost B-tree
> node were actually deleted.
> Possible improvements:
>   1. Implement backwards scan in the B-trees (this is also suggested
>      in the comments in BTreeMaxScan).
>   2. Go up to the parent node and down to the next leaf node on the
>      left side, and continue until a valid max value is found. In
>      Derby, traversing up in a B-tree is not allowed, but would it be
>      ok to go up if the latches were kept on the higher-level nodes in
>      the tree? Of course, this would have negative impact on
>      concurrency.
>   3. Right-to-left traversal on the leaf level is possible (using
>      ControlRow.getLeftSibling()), but will throw an exception if the
>      page cannot be latched without waiting. It is therefore possible
>      to try a right-to-left search for the max value, and only fall
>      back to the left-to-right approach if a conflict arises.

-- 
This message is automatically generated by JIRA.
-
If you think it was sent incorrectly contact one of the administrators: http://issues.apache.org/jira/secure/Administrators.jspa
-
For more information on JIRA, see: http://www.atlassian.com/software/jira

        

Mime
View raw message