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https://issues.apache.org/jira/browse/DERBY-4971?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12981755#action_12981755
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Knut Anders Hatlen commented on DERBY-4971:
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It looks like the problem here is that the optimizer is slow, not that it picks
a bad plan. Most of the time is spent preparing the statement. The time spent
executing it (or re-executing an already prepared statement) is similar for the
two:
When optimizer chooses join order:
ij version 10.7
ij> connect 'jdbc:derby:rita.derby;user=rita';
ij> elapsedtime on;
ij> prepare ps as '
SELECT journey.transport_company AS journey_transport_provider,
(...)
FROM
movement AS dispatched
(...)
ELAPSED TIME = 45034 milliseconds
ij> execute ps;
(...)
1 row selected
ELAPSED TIME = 2084 milliseconds
ij> execute ps;
(...)
1 row selected
ELAPSED TIME = 693 milliseconds
ij> execute ps;
(...)
1 row selected
ELAPSED TIME = 353 milliseconds
Fixed join order:
ij version 10.7
ij> connect 'jdbc:derby:rita.derby;user=rita';
ij> elapsedtime on;
ij> prepare ps as '
SELECT journey.transport_company AS journey_transport_provider,
(...)
FROM -- DERBY-PROPERTIES joinOrder = FIXED
movement AS dispatched
(...)
ELAPSED TIME = 3684 milliseconds
ij> execute ps;
(...)
1 row selected
ELAPSED TIME = 2325 milliseconds
ij> execute ps;
(...)
1 row selected
ELAPSED TIME = 485 milliseconds
ij> execute ps;
(...)
1 row selected
ELAPSED TIME = 380 milliseconds
(...)
1 row selected
ELAPSED TIME = 291 milliseconds
> Query runs 10 times more slowly with optimizer turned ON
> --------------------------------------------------------
>
> Key: DERBY-4971
> URL: https://issues.apache.org/jira/browse/DERBY-4971
> Project: Derby
> Issue Type: Bug
> Components: SQL
> Affects Versions: 10.7.1.1
> Reporter: Chris Wilson
> Attachments: optimizer-off.sql, optimizer-on.sql, rita.derby.zip
>
>
> Derby takes 10 times as long to execute the attached query on the attached
> database when the optimizer is allowed to choose its own join order.
> chris@fen-desktop2(tmp)$ cat ij
> #!/bin/sh
> DERBY_DIR=/home/chris/.m2/repository/org/apache/derby
> DERBY_VER=10.7.1.1
> DERBY_JAR=$DERBY_DIR/derby/$DERBY_VER/derby-$DERBY_VER.jar
> TOOLS_JAR=$DERBY_DIR/derbytools/$DERBY_VER/derbytools-$DERBY_VER.jar
> java -cp $DERBY_JAR:$TOOLS_JAR $OPTIONS org.apache.derby.tools.ij "$@"
> chris@fen-desktop2(tmp)$ time ./ij optimizer-on.sql
> ij version 10.7
> ij> connect 'jdbc:derby:;databaseName=/tmp/rita.derby;user=rita';
> ij> SELECT journey.transport_company AS journey_transport_provider, ...
> 1 row selected
> ij> quit;
> real 0m47.459s
> user 0m47.067s
> sys 0m0.344s
> chris@fen-desktop2(tmp)$ time ./ij optimizer-off.sql
> ...
> real 0m3.913s
> user 0m4.100s
> sys 0m0.148s
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