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From "Daniel John Debrunner (JIRA)" <derby-...@db.apache.org>
Subject [jira] Commented: (DERBY-421) starting an XA transaction resets the isolation level set with SET CURRENT ISOLATION
Date Mon, 01 Aug 2005 21:36:37 GMT
    [ http://issues.apache.org/jira/browse/DERBY-421?page=comments#action_12317372 ] 

Daniel John Debrunner commented on DERBY-421:
---------------------------------------------

State information is kept in BrokeredConnection for this reason (comment in BrokeredConnection)
	/**
		Maintain state as seen by this Connection handle, not the state
		of the underlying Connection it is attached to.
	*/

To expand on that, an application getting a Connection C from an XADataSource/XAConnection
can use C in local mode or in global mode. The application can set  C's state with various
setXXX calls, and thus the applcation has expectation of what the state is. When C is connected
to a local transaction, the state of the connection needs to match any state set by the application.
When C is attached an existing  global transaction the C's state needs to match that of the
exsiting transaction, not the state as expected by the application. Then when reverting to
local mode,  the state needs to be reset as the application expects it.
Here's a simple example.

c.setReadOnly(true);
// do some local work

// now attach to an existing global transaction
c.isReadOnly(); // returns false as the transaction has included modifications

// now detach from the global transaction

// This is the critical point
c..isReadOnly();  // needs to return true because that's what the application is expecting

Thus the BrokeredConnection maintains the state that it needs to set on the new local underlying
EmbedConnection object to ensure its state is in sync with the application's expectation.
This is also because the Derby embedded implementation always creates a new EmbedConnection
object when switching from global to local.

> starting an XA transaction resets the isolation level set with SET CURRENT ISOLATION
> ------------------------------------------------------------------------------------
>
>          Key: DERBY-421
>          URL: http://issues.apache.org/jira/browse/DERBY-421
>      Project: Derby
>         Type: Sub-task
>     Reporter: Kathey Marsden

>
> When an XA Transaction is started the isolation level set with SET CURRENT ISOLATION
gets reset to CS.
> Embedded setTransactionIsolation  does not have this problem but this problem is the
root cause of DERBY-414 because client implements setTransactionIsolation by sending SET CURRENT
ISOLATION
> $ java TestSetCurrentIsolation
> Database product: Apache Derby
> Database version: 10.2.0.0 alpha
> Driver name:      Apache Derby Embedded JDBC Driver
> Driver version:   10.2.0.0 alpha
> SET CURRENT ISOLATION = UR
> CURRENT ISOLATION: UR
> getTransactionIsolation:TRANSACTION_READ_UNCOMMITTED:1
> Isolation level after xa start
> CURRENT ISOLATION: CS
> getTransactionIsolation:TRANSACTION_READ_COMMITTED:2
> $
> import java.sql.*;
> import javax.sql.*;
> import javax.transaction.xa.*;
> public class TestSetCurrentIsolation
> {
>     public static void main(String[] args) throws Throwable
>     {
>         try
>         {
>              final org.apache.derby.jdbc.EmbeddedXADataSource ds =
>              new org.apache.derby.jdbc.EmbeddedXADataSource();
>              ds.setDatabaseName("C:\\drivers\\derby\\databases\\SCHEDDB");
>              ds.setUser("dbuser1");
>              ds.setPassword("******");
>             XAConnection xaConn = ds.getXAConnection();
>             Connection conn = xaConn.getConnection();
>             conn.setAutoCommit(true);
>             System.out.println("Database product: " + conn.getMetaData().getDatabaseProductName());
>             System.out.println("Database version: " + conn.getMetaData().getDatabaseProductVersion());
>             System.out.println("Driver name:      " + conn.getMetaData().getDriverName());
>             System.out.println("Driver version:   " + conn.getMetaData().getDriverVersion());
>             Statement stmt = conn.createStatement();
>             System.out.println("SET CURRENT ISOLATION = UR");
>             stmt.executeUpdate("SET CURRENT ISOLATION = UR");
>             showIsolationLevel(conn);
>             conn.setAutoCommit(false);
>             XAResource xaRes = xaConn.getXAResource();
>             Xid xid = new TestXid(1,(byte) 32, (byte) 32);
>             xaRes.start(xid, XAResource.TMNOFLAGS);
>             System.out.println("Isolation level after xa start");
>             showIsolationLevel(conn);
>             
>             xaRes.end(xid, XAResource.TMSUCCESS);
>             xaRes.rollback(xid);
>             conn.close();
>             xaConn.close();
>         }
>         catch (SQLException sqlX)
>         {
>             System.out.println("Error on thread 1.");
>             do sqlX.printStackTrace();
>             while ((sqlX = sqlX.getNextException()) != null);
>         }
>         catch (Throwable th)
>         {
>             System.out.println("Error on thread 1.");
>             do th.printStackTrace();
>             while ((th = th.getCause()) != null);
>         }
>     }
> 	/**
> 	 * @param conn
> 	 * @throws SQLException
> 	 */
> 	private static void showIsolationLevel(Connection conn) throws SQLException {
> 		PreparedStatement ps = conn.prepareStatement("VALUES CURRENT ISOLATION");
> 		ResultSet rs = ps.executeQuery();
> 		//ResultSet rs = conn.createStatement().executeQuery("VALUES CURRENT ISOLATION");
> 		rs.next();
> 		System.out.println("CURRENT ISOLATION: " +  rs.getString(1));
> 		System.out.println("getTransactionIsolation:" + 
> 					getIsoLevelName(conn.getTransactionIsolation()));						
> 	}
> 	
> 	public static String getIsoLevelName(int level)
> 	{
> 		switch (level) {
> 			case java.sql.Connection.TRANSACTION_REPEATABLE_READ:
> 				return "TRANSACTION_REAPEATABLE_READ:" + level;
> 					
> 			case java.sql.Connection.TRANSACTION_READ_COMMITTED:
> 				return "TRANSACTION_READ_COMMITTED:" + level;
> 			case java.sql.Connection.TRANSACTION_SERIALIZABLE:
> 				return "TRANSACTION_SERIALIZABLE:" + level;
> 			case java.sql.Connection.TRANSACTION_READ_UNCOMMITTED:
> 				return "TRANSACTION_READ_UNCOMMITTED:" + level;
> 		}
> 		return "UNEXPECTED_ISO_LEVEL";
> 	}
> }

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