Re: No exception with concurrent updates

Dear all,

I wrote (extremely) simple programme in Java (jsdk1.4.2) to examine the
PostgreSQL's (v7.2.4, I know, rather obsolete) handling of concurrent
updates and I'm confused with the fact that the server (running on a remote
machine with Red Hat Linux 6.0) does not give me any kind of exception when
I execute the following code on the client machine running Win 2000. While
running the programme in the debug mode the excution just hangs when the
UPDATE query of the transaction2() is executed. Using setQueryTimeout()
won't help much since it is available as of 7.3 version, isn't it. I set
autocommit off and specify TRANSACTION_SERIALIZABLE on the Connection
objects. I'm using the pg73jdbc3.jar and NetBeans 3.5.

/*
* ConcurencyTest.java
* Created on 09 July 2004, 15:39
*/
import java.sql.*;

public class ConcurrencyTest
{
Connection con1, con2;

public ConcurrencyTest()
{
/*
ConnectionManager object creates Connection and the
GetConnection() method returns the reference. Value of
128 specifies the JDBC connection (rather than ODBC).
*/
con1 = new ConnectionManager(128).GetConnection();
con2 = new ConnectionManager(128).GetConnection();

transaction1();
transaction2();

try
{
con2.commit();
con1.commit();
//con1.close();
//con2.close();
}
catch (SQLException sqle)
{
System.out.println("Could not close the connection");
}

}

public void transaction1()
{
try
{
con1.commit();
Statement sta1 = con1.createStatement();
sta1.setQueryTimeout(5);

rs_1 = sta1.executeQuery("SELECT * FROM Orderline WHERE ol_o_id
= 1 AND ol_d_id = 1 AND ol_w_id = 1 AND ol_number = 4");

while (rs_1.next())
System.out.println(rs_1.getInt(8) + "\tT1");
rs_1.close();

sta1.executeUpdate("UPDATE Orderline SET ol_quantity = 10 WHERE
ol_o_id = 1 AND ol_d_id = 1 AND ol_w_id = 1 AND ol_number = 4");

sta1.close();
}
catch (SQLException sqle)
{
System.out.println("Error in Transaction 1: " + sqle);
}

}

public void transaction2()
{
try
{
con2.commit();
Statement sta2 = con2.createStatement();
sta2.setQueryTimeout(5);

ResultSet rs_2 = sta2.executeQuery("SELECT * FROM Orderline
WHERE ol_o_id = 1 AND ol_d_id = 1 AND ol_w_id = 1 AND ol_number = 4");
while (rs_2.next())
System.out.println(rs_2.getInt(8) + "\tT2");
rs_2.close();


sta2.executeUpdate("UPDATE Orderline SET ol_quantity = 20 WHERE
ol_o_id = 1 AND ol_d_id = 1 AND ol_w_id = 1 AND ol_number = 4");

sta2.close();
}
catch (SQLException sqle)
{
System.out.println("Error in Transaction 2: " + sqle);

}

}

public static void main(String args[])
{
new ConcurrencyTest();
}
}

Vladimir,

Have you read how concurrency works in postgresql ?

Dave
On Wed, 2004-07-14 at 12:59, Vladimir Stankovic wrote:
> Dear all,
>
> I wrote (extremely) simple programme in Java (jsdk1.4.2) to examine the
> PostgreSQL's (v7.2.4, I know, rather obsolete) handling of concurrent
> updates and I'm confused with the fact that the server (running on a remote
> machine with Red Hat Linux 6.0) does not give me any kind of exception when
> I execute the following code on the client machine running Win 2000. While
> running the programme in the debug mode the excution just hangs when the
> UPDATE query of the transaction2() is executed. Using setQueryTimeout()
> won't help much since it is available as of 7.3 version, isn't it. I set
> autocommit off and specify TRANSACTION_SERIALIZABLE on the Connection
> objects. I'm using the pg73jdbc3.jar and NetBeans 3.5.
>
> /*
> * ConcurencyTest.java
> * Created on 09 July 2004, 15:39
> */
> import java.sql.*;
>
> public class ConcurrencyTest
> {
> Connection con1, con2;
>
> public ConcurrencyTest()
> {
> /*
> ConnectionManager object creates Connection and the
> GetConnection() method returns the reference. Value of
> 128 specifies the JDBC connection (rather than ODBC).
> */
> con1 = new ConnectionManager(128).GetConnection();
> con2 = new ConnectionManager(128).GetConnection();
>
> transaction1();
> transaction2();
>
> try
> {
> con2.commit();
> con1.commit();
> //con1.close();
> //con2.close();
> }
> catch (SQLException sqle)
> {
> System.out.println("Could not close the connection");
> }
>
> }
>
> public void transaction1()
> {
> try
> {
> con1.commit();
> Statement sta1 = con1.createStatement();
> sta1.setQueryTimeout(5);
>
> rs_1 = sta1.executeQuery("SELECT * FROM Orderline WHERE ol_o_id
> = 1 AND ol_d_id = 1 AND ol_w_id = 1 AND ol_number = 4");
>
> while (rs_1.next())
> System.out.println(rs_1.getInt(8) + "\tT1");
> rs_1.close();
>
> sta1.executeUpdate("UPDATE Orderline SET ol_quantity = 10 WHERE
> ol_o_id = 1 AND ol_d_id = 1 AND ol_w_id = 1 AND ol_number = 4");
>
> sta1.close();
> }
> catch (SQLException sqle)
> {
> System.out.println("Error in Transaction 1: " + sqle);
> }
>
> }
>
> public void transaction2()
> {
> try
> {
> con2.commit();
> Statement sta2 = con2.createStatement();
> sta2.setQueryTimeout(5);
>
> ResultSet rs_2 = sta2.executeQuery("SELECT * FROM Orderline
> WHERE ol_o_id = 1 AND ol_d_id = 1 AND ol_w_id = 1 AND ol_number = 4");
> while (rs_2.next())
> System.out.println(rs_2.getInt(8) + "\tT2");
> rs_2.close();
>
>
> sta2.executeUpdate("UPDATE Orderline SET ol_quantity = 20 WHERE
> ol_o_id = 1 AND ol_d_id = 1 AND ol_w_id = 1 AND ol_number = 4");
>
>
> sta2.close();
> }
> catch (SQLException sqle)
> {
> System.out.println("Error in Transaction 2: " + sqle);
>
> }
>
> }
>
> public static void main(String args[])
> {
> new ConcurrencyTest();
> }
> }
>
>
>
>
>
> ---------------------------(end of broadcast)---------------------------
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> joining column's datatypes do not match
>
>
>
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>
>
--
Dave Cramer
519 939 0336
ICQ # 14675561