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https://issues.apache.org/jira/browse/DERBY-3498?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12575482#action_12575482
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army edited comment on DERBY-3498 at 3/5/08 12:10 PM:
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I notice that run/Populate.java has a parameter "createConstraintsBeforeLoad"
which defaults to "true", meaning that all indexes are created BEFORE data is
loaded. Is that parameter overridden by the "junit-system-mini-codeline-jars"
target? If not, then it's possible that the statistics for the tables are
completely wrong (known issue in Derby when indexes are created before data is
loaded), which could cause the optimizer to pick a bad plan.
If keeping "createConstraintsBeforeLoad()" is important to the test, then it
might be good to add some calls to compress the tables after the load
completes, so that the stats are updated accordingly. That might (hopefully)
help things a bit...
was (Author: army):
I notice that run/Populate.java has a parameter
"createConstraintsBeforeLoad" which defaults to "true", meaning that all
indexes are created BEFORE data is loaded. Is that parameter overridden by the
"junit-system-mini-codeline-jars" target?
> 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():
> SELECT D.D_ID, D.D_W_ID,D.D_NEXT_O_ID,
> 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 W_ID, D_ID, O_ID.
> 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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