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Date: Wed, 12 Apr 2006 00:30:25 +0100 (BST)
From: "Mike Matrigali (JIRA)" <derby-dev@db.apache.org>
To: derby-dev@db.apache.org
Subject: [jira] Updated: (DERBY-979) NullPointerException in store when
 using holdable resultset to get next tuple on a deleted table
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     [ http://issues.apache.org/jira/browse/DERBY-979?page=all ]

Mike Matrigali updated DERBY-979:
---------------------------------

    Component: Store

> NullPointerException in store when using holdable resultset to get next tuple on a deleted table
> ------------------------------------------------------------------------------------------------
>
>          Key: DERBY-979
>          URL: http://issues.apache.org/jira/browse/DERBY-979
>      Project: Derby
>         Type: Bug

>   Components: Store
>  Environment: All
>     Reporter: Andreas Korneliussen
>     Priority: Minor

>
> Derby uses table intent locks to prevent a table from being dropped while there is an open cursor on it.
> However, for holdable cursors, the lock is released after the commit. This allows a drop table command to drop the table.  The next call to ResultSet.next then get a NullPointerException from the store module.
> A potential fix, could be to handle this situation in store, and to give a meaningful error message.
> Transaction history:
> T1: select * from table1 
> T1: cursor.next()
> T1: commit
> T2: drop table table1
> T2: commit
> T3: cursor.next()..
> Result: T3 get NullPointerException.
> To reproduce: Add the following testcase to ConcurrencyTest.java (see DERBY-934) (hopefully someone commits those tests soon)
>   /**
>      * Test that as long as an cursor is open on a table, no
>      * other transaction can delete the table.
>      */
>     public void testTableIntentLockWithHoldableCursor() 
>         throws SQLException
>     {
>         con.setTransactionIsolation(Connection.TRANSACTION_READ_UNCOMMITTED);
>         con.setAutoCommit(true); 
>         Statement s = con.createStatement(ResultSet.TYPE_FORWARD_ONLY, 
>                                           ResultSet.CONCUR_UPDATABLE);
>         ResultSet rs = s.executeQuery("select * from t1");
>         rs.next();
>         updateTuple(rs);
>         con.commit();
>         
>         Connection con2 = getNewConnection();
>         con2.setTransactionIsolation(Connection.TRANSACTION_READ_COMMITTED);
>         
>         try {
>             PreparedStatement ps2 = con2.prepareStatement
>                 ("drop table t1");
>             ps2.executeUpdate();
>             con2.commit();
>                         
>             // .. WHAT happens ?
>             rs.next();
>             updateTuple(rs);
>         } catch (SQLException e) {
>             System.out.println(e.getMessage() + ":" + e.getSQLState());
>             printStackTrace(e);
>             assertEquals("Unexpected SQL state",  LOCK_TIMEOUT_SQL_STATE,
>                          e.getSQLState());
>         } finally {
>             con2.close();
>         }          
>     }
> java.lang.NullPointerException
>         at org.apache.derby.impl.store.access.conglomerate.OpenConglomerate.latchPageAndRepositionScan(OpenConglomerate.java:264)
>         at org.apache.derby.impl.store.access.conglomerate.GenericScanController.fetchRows(GenericScanController.java:613)
>         at org.apache.derby.impl.store.access.heap.HeapScan.fetchNext(HeapScan.java:207)
>         at org.apache.derby.impl.sql.execute.TableScanResultSet.getNextRowCore(TableScanResultSet.java:681)
>         at org.apache.derby.impl.sql.execute.BasicNoPutResultSetImpl.getNextRow(BasicNoPutResultSetImpl.java:474)
>         at org.apache.derby.impl.jdbc.EmbedResultSet.movePosition(EmbedResultSet.java:371)
>         at org.apache.derby.impl.jdbc.EmbedResultSet.next(EmbedResultSet.java:320)
>         at org.apache.derbyTesting.functionTests.tests.jdbcapi.ConcurrencyTest.testTableIntentLockWithHoldableCursor(ConcurrencyTest.java:877)
> ..
> The NullPointerException is wrapped in a SQLException, which just makes the bug more confusing for the user.

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