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From Pavel Bortnovskiy <pbortnovs...@jefferies.com>
Subject NPE
Date Mon, 10 Dec 2012 17:23:37 GMT
Hello:

While testing my application, which uses Derby in memory-only mode, I get NPE inside Derby
under "mysterious" circumstances.
At this point, I can't even figure out what's triggering it and where this could happen, but
let me preempt my troubleshooting with some stack traces. Perhaps someone, with good knowledge
of Derby's code, may offer some explanation. Here are some stack traces:

Mon Dec 10 12:12:36 EST 2012 Thread[DatabasePublisher[WRITER],5,main] (XID = 235), (SESSIONID
= 5), (DATABASE = memory:test), (DRDAID = null), Failed Statement is: select * from READER
java.lang.NullPointerException
       at org.apache.derby.impl.store.access.conglomerate.GenericScanController.reopenAfterEndTransaction(Unknown
Source)
       at org.apache.derby.impl.store.access.conglomerate.GenericScanController.fetchRows(Unknown
Source)
       at org.apache.derby.impl.store.access.heap.HeapScan.fetchNextGroup(Unknown Source)
       at org.apache.derby.impl.sql.execute.BulkTableScanResultSet.reloadArray(Unknown Source)
       at org.apache.derby.impl.sql.execute.BulkTableScanResultSet.getNextRowCore(Unknown
Source)
       at org.apache.derby.impl.sql.execute.ProjectRestrictResultSet.getNextRowCore(Unknown
Source)
       at org.apache.derby.impl.sql.execute.ScrollInsensitiveResultSet.getNextRowFromSource(Unknown
Source)
       at org.apache.derby.impl.sql.execute.ScrollInsensitiveResultSet.getNextRowCore(Unknown
Source)
       at org.apache.derby.impl.sql.execute.BasicNoPutResultSetImpl.getNextRow(Unknown Source)
       at org.apache.derby.impl.jdbc.EmbedResultSet.movePosition(Unknown Source)
       at org.apache.derby.impl.jdbc.EmbedResultSet.next(Unknown Source)
       at QueryResults$1.hasNext(QueryResults.java:268)
       at DatabasePublisher.process(DatabasePublisher.java:318)
       at java.lang.Thread.run(Thread.java:662)

or

2012-12-10 12:12:36,537 [DatabasePublisher[WRITER]] ERROR QueryResults  - Unable to execute
ResultSet.next() for Statement ""select * from READER" [DERBY]"
java.sql.SQLException: Java exception: ': java.lang.NullPointerException'.
       at org.apache.derby.impl.jdbc.SQLExceptionFactory40.getSQLException(Unknown Source)
       at org.apache.derby.impl.jdbc.Util.newEmbedSQLException(Unknown Source)
       at org.apache.derby.impl.jdbc.Util.javaException(Unknown Source)
       at org.apache.derby.impl.jdbc.TransactionResourceImpl.wrapInSQLException(Unknown Source)
       at org.apache.derby.impl.jdbc.TransactionResourceImpl.handleException(Unknown Source)
       at org.apache.derby.impl.jdbc.EmbedConnection.handleException(Unknown Source)
       at org.apache.derby.impl.jdbc.ConnectionChild.handleException(Unknown Source)
       at org.apache.derby.impl.jdbc.EmbedResultSet.closeOnTransactionError(Unknown Source)
       at org.apache.derby.impl.jdbc.EmbedResultSet.movePosition(Unknown Source)
       at org.apache.derby.impl.jdbc.EmbedResultSet.next(Unknown Source)
       at QueryResults$1.hasNext(QueryResults.java:268)
       at DatabasePublisher.process(DatabasePublisher.java:318)
       at java.lang.Thread.run(Thread.java:662)
Caused by: java.sql.SQLException: Java exception: ': java.lang.NullPointerException'.
       at org.apache.derby.impl.jdbc.SQLExceptionFactory.getSQLException(Unknown Source)
       at org.apache.derby.impl.jdbc.SQLExceptionFactory40.wrapArgsForTransportAcrossDRDA(Unknown
Source)
       ... 14 more
Caused by: java.lang.NullPointerException
       at org.apache.derby.impl.store.access.conglomerate.GenericScanController.reopenAfterEndTransaction(Unknown
Source)
       at org.apache.derby.impl.store.access.conglomerate.GenericScanController.fetchRows(Unknown
Source)
       at org.apache.derby.impl.store.access.heap.HeapScan.fetchNextGroup(Unknown Source)
       at org.apache.derby.impl.sql.execute.BulkTableScanResultSet.reloadArray(Unknown Source)
       at org.apache.derby.impl.sql.execute.BulkTableScanResultSet.getNextRowCore(Unknown
Source)
       at org.apache.derby.impl.sql.execute.ProjectRestrictResultSet.getNextRowCore(Unknown
Source)
       at org.apache.derby.impl.sql.execute.ScrollInsensitiveResultSet.getNextRowFromSource(Unknown
Source)
       at org.apache.derby.impl.sql.execute.ScrollInsensitiveResultSet.getNextRowCore(Unknown
Source)
       at org.apache.derby.impl.sql.execute.BasicNoPutResultSetImpl.getNextRow(Unknown Source)
       ... 6 more


One more thing I can share is that this seems to also be a timing problem - if the code is
executed slowly, line-by-line in the debugger, then this problem doesn't occur. But if run
at full speed, then these exceptions are thrown. The problem is not intermittent and easily
reproduced 100% of the time on my end.

Any thoughts would be greatly appreciated.

Pavel.

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