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From "A B (JIRA)" <j...@apache.org>
Subject [jira] Commented: (DERBY-3033) select query results in nullpointer exception in skipScan()
Date Mon, 24 Sep 2007 17:14:50 GMT

    [ https://issues.apache.org/jira/browse/DERBY-3033?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12529919
] 

A B commented on DERBY-3033:
----------------------------

> It's tricky because the optimizer overrides are specified on the query
> before it's been flattened, but I want to force a particular join order
> after flattening. 

Hmm...not sure if that's possible with current override support or not?

One thing that influences join order is the relative size of the tables in question.  I noticed
that for the original database, the row counts are:

  DSR: 3240
  ST: 20
  dispatcher_locks: 0

while in the database for "repro2" they are:

  DSR: 1005
  ST: 10003
  dispatcher_locs: 0

Notice how DSR is 15x as large as ST in the first case, while ST is 10x as large as DSR in
the second case.  Perhaps that has something to do with why the optimizer chooses different
join orders for the two repros...?

> select query results in nullpointer exception in skipScan()
> -----------------------------------------------------------
>
>                 Key: DERBY-3033
>                 URL: https://issues.apache.org/jira/browse/DERBY-3033
>             Project: Derby
>          Issue Type: Bug
>          Components: SQL
>    Affects Versions: 10.2.2.0
>         Environment: Windows XP, Java 5.0, JDBC, Derby 10.2.2.0
>            Reporter: Haolan Qin
>            Assignee: Bryan Pendleton
>         Attachments: bug4736.sql, d3033-sane-ij-session-10.3.1.5.txt, generatedActivation.txt,
noClosureOfNotExists.diff, query_plan.new, query_plan.old, queryPlanRS.txt, repro2.java, test.rar,
test.zip, viewer_10_1.zip
>
>
> The following error was repeatedly thrown when we tried to run a select query via JDBC.
Strangely, the exact same select query did not trigger any error when run from the command
line console. After we added an index, the error went away completely. 
> java.lang.NullPointerException
>  at org.apache.derby.impl.sql.execute.NoPutResultSetImpl.skipScan(Unknown Source)
>  at org.apache.derby.impl.sql.execute.TableScanResultSet.openCore(Unknown Source)
>  at org.apache.derby.impl.sql.execute.IndexRowToBaseRowResultSet.openCore(Unknown Source)
>  at org.apache.derby.impl.sql.execute.ProjectRestrictResultSet.openCore(Unknown Source)
>  at org.apache.derby.impl.sql.execute.JoinResultSet.openRight(Unknown Source)
>  at org.apache.derby.impl.sql.execute.JoinResultSet.openCore(Unknown Source)
>  at org.apache.derby.impl.sql.execute.ProjectRestrictResultSet.openCore(Unknown Source)
>  at org.apache.derby.impl.sql.execute.SortResultSet.openCore(Unknown Source)
>  at org.apache.derby.impl.sql.execute.ProjectRestrictResultSet.openCore(Unknown Source)
>  at org.apache.derby.impl.sql.execute.BasicNoPutResultSetImpl.open(Unknown Source)
>  at org.apache.derby.impl.sql.GenericPreparedStatement.execute(Unknown Source)
>  at org.apache.derby.impl.jdbc.EmbedStatement.executeStatement(Unknown Source)
>  at org.apache.derby.impl.jdbc.EmbedPreparedStatement.executeStatement(Unknown Source)
>  at org.apache.derby.impl.jdbc.EmbedPreparedStatement.execute(Unknown Source)
>  at org.apache.derby.impl.drda.DRDAStatement.execute(Unknown Source)
>  at org.apache.derby.impl.drda.DRDAConnThread.processCommands(Unknown Source)
>  at org.apache.derby.impl.drda.DRDAConnThread.run(Unknown Source)

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