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From "Dag H. Wanvik (Updated) (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (DERBY-3823) NullPointerException in stress.multi test
Date Thu, 06 Oct 2011 03:20:30 GMT

     [ https://issues.apache.org/jira/browse/DERBY-3823?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Dag H. Wanvik updated DERBY-3823:
---------------------------------

    Attachment: d3823-1.diff

Uploading a trial patch to EmbedPreparedStatement#getMetaData which changes the logic to detect
if a prepared statement has been/is the the process of being recompiled as we are trying to
get the metadata. It should avoid the race condition in the existign code where it can happen
that we try to get the ps's activation class while it is being recompiled (hence is null temporarily).

Even if with the patch, we get a consistent picture of the ps's current activation class and
result description (my hope), I am not sure I understand how this approach is always correct:
We are trying to get metadata for a result set. If the prepared statement has been invalidated
(i.e. recompiled), I wonder if the ResultDescription will still necessarily be correct for
that result set? Perhaps it will, since if the some change were to occur to the table that
would change the column information, presumably, such changes would block on the fact that
the result set was still open (?). At least on embedded that seems reasonable assumption.
On client/server I think we can possible close the result set as a result of prefetching rows,
so I am not sure if this always holds. But maybe the retrieval of the metadata happens before
the time the result set is closed.. Can anyone shed light on this?

In any case, I will try to run the test for some time with the new patch and see what happens...

                
> NullPointerException in stress.multi test
> -----------------------------------------
>
>                 Key: DERBY-3823
>                 URL: https://issues.apache.org/jira/browse/DERBY-3823
>             Project: Derby
>          Issue Type: Bug
>          Components: Network Server
>    Affects Versions: 10.3.3.1, 10.7.1.1, 10.8.1.2
>            Reporter: Kathey Marsden
>              Labels: derby_triage10_5_2
>         Attachments: d3823-1.diff, derby.log
>
>
> I saw the following NPE in stress.multi running on 10.3 with derbyclient.
> java.lang.NullPointerException
>         at org.apache.derby.impl.jdbc.EmbedPreparedStatement.getMetaData(Unknown
>  Source)
>         at org.apache.derby.impl.drda.DRDAConnThread.writeSQLDARD(Unknown Source
> )
>         at org.apache.derby.impl.drda.DRDAConnThread.processCommands(Unknown Sou
> rce)
>         at org.apache.derby.impl.drda.DRDAConnThread.run(Unknown Source)
> Cleanup action completed

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