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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 Tue, 18 Sep 2007 15:31:43 GMT

    [ https://issues.apache.org/jira/browse/DERBY-3033?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12528416
] 

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

> I played around with the skipScan repro case and confirmed Kathey's suspicion
> about BaseActivation.getColumnFromRow

Thank you for your continued investigation of this issue, Bryan.  It's great to have an idea
of the codepath in question here.  Have you had the time/inclination to look into the cause
of the null value in row[rsNumber]?  I realize that's easy to say and quite hard to do, but
I was just wondering if you've looked at it, or if you have the time and plans to do so?

In particular, I'm referring to the code comment that Kathey mentioned:

  "NoPutResultSetImpl.clearOrderableCache attempts to prefetch invariant values
   into a cache. This fails in some deeply nested joins."

I think the core question here is *why* does "this fail in some deeply nested joins"?  That
sounds awfully suspicious.  It seems that either a) the "failure" is acceptable and the comments
need to be updated, in which case Kathey's "quick fix" of checking for the null value would
be appropriate; or b) the "failure" is a bug and in order to solve this issue, that failure
should (ideally) be fixed...

Would you agree?

> 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
>         Attachments: bug4736.sql, d3033-sane-ij-session-10.3.1.5.txt, query_plan.new,
query_plan.old, 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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