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From "Daniel John Debrunner (JIRA)" <j...@apache.org>
Subject [jira] Commented: (DERBY-3498) Performance sensitive to FROM order list in three way join with GROUP BY
Date Wed, 05 Mar 2008 20:13:42 GMT

    [ https://issues.apache.org/jira/browse/DERBY-3498?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12575486#action_12575486

Daniel John Debrunner commented on DERBY-3498:

Indexes and constraints are created before the load in this case.

> Performance sensitive to FROM order list in three way join with GROUP BY
> ------------------------------------------------------------------------
>                 Key: DERBY-3498
>                 URL: https://issues.apache.org/jira/browse/DERBY-3498
>             Project: Derby
>          Issue Type: Bug
>          Components: Performance, SQL
>            Reporter: Daniel John Debrunner
>            Priority: Minor
> The Order Entry system test has this query in Checks.testCondition2():
>                         MAX(O.O_ID),MAX(N.NO_O_ID) FROM NEWORDERS N, 
>                         DISTRICT D, ORDERS O WHERE D.D_W_ID=O.O_W_ID 
>                         AND D.D_W_ID = N.NO_W_ID AND D.D_ID = O.O_D_ID 
>                         AND D.D_ID = N.NO_D_ID GROUP BY 
>                         D.D_ID,D.D_W_ID,D.D_NEXT_O_ID
> Changing the FROM list to put DISTRICT first reduced the running time from ~138seconds
to ~105 and a similar reduction on another machine.
> (with a 1 warehouse database)
> Beyond that, the query seems to take too long. 10 rows will be returned and for each
district row (returned row) the MAX() values in the select list should just be a max lookup
in the primary key for the ORDERS and NEWORDERS table. The primary key for these tables is
> Thus it should be a scan of the 10 row DISTRICT table with 20 index lookups, hard to
see how that should table 100 seconds.
> One can see this by using the java-system-mini-codeline-jars target.

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