I've been playing with async notifications lately, and I've found a
small problem: when several notifications are issued at once (for
example within a transaction) normally only one of those gets to the
client. The rest of the notifications are not received until
something happens on the connection, for example a query or another
notification. I'm using the latest CVS, updated yesterday. I've
looked over the code, and there's nothing obvious. I think that this
has to do with java's handling of sockets, as the C example that deals
with notifications works fine. It seems that some packages are
"stuck" in the socket, but my knowledge of sockets is very limited. A
possible workarround would be to issue the simplest possible query or
message to the backend when a notification is found, to see if anymore
notifications are "stuck". This would generate a little bit of extra
traffic, but only when there is a notification. Here is a small test
case showing what's happening:
public class TestAsync extends TestCase {
Connection conn2,conn1;
public void testAsync() {
String user = "andres";
String pass = "";
String url = "jdbc:postgresql://127.0.0.1/template1";
try {
Class.forName("org.postgresql.Driver");
} catch (ClassNotFoundException cnf) {
fail("Data Base Driver not Found: " + cnf.getMessage());
}
try {
conn1 = DriverManager.getConnection(url, user, pass);
conn2 = DriverManager.getConnection(url, user, pass);
conn2.setAutoCommit(true);
Statement stmt2 = conn2.createStatement();
stmt2.execute("LISTEN test1");
stmt2.execute("LISTEN test2");
stmt2.execute("LISTEN test3");
PGConnection pgconn = (PGConnection) conn2;
Statement stmt1=conn1.createStatement();
stmt1.execute("NOTIFY test1;");
stmt1.execute("NOTIFY test2;");
stmt1.execute("NOTIFY test3;");
conn1.commit();
PGNotification[] nots = pgconn.getNotifications();
assertEquals(3,nots.length);
} catch (SQLException sqle) {
fail("SQLException sql" + sqle.getLocalizedMessage());
}
}
I'm running a 7.4 backend, but I don't think that's the problem. But
if someone thinks I'm doing something wrong, please let me know!!
thanks to all of the people that have worked on PostreSQL
Andres Olarte
