Enabling Native Connection Load Balancing in JDBC
Native connection load balancing helps spread the overhead caused by client connections on the hosts in the Vertica database. Both the server and the client must enable native connection load balancing in order for it to have an effect. If both have enabled it, then when the client initially connects to a host in the database, the host picks a host to handle the client connection from a list of the currently up hosts in the database, and informs the client which host it has chosen.
If the initially-contacted host did not choose itself to handle the connection, the client disconnects, then opens a second connection to the host selected by the first host. The connection process to this second host proceeds as usual—if SSL is enabled, then SSL negotiations begin, otherwise the client begins the authentication process. See About Native Connection Load Balancing in the Administrator's Guide for details.
To enable native load balancing on your client, set the ConnectionLoadBalance connection parameter to true. The following example demonstrates connecting to the database several times with native connection load balancing enabled and fetching the name of the node handling the connection from the V_MONITOR.CURRENT_SESSION system table.
import java.sql.*;
import java.util.Properties;
import java.sql.*;
import java.util.Properties;
public class JDBCLoadingBalanceExample {
public static void main(String[] args) {
Properties myProp = new Properties();
myProp.put("user", "dbadmin");
myProp.put("password", "example_password123");
myProp.put("loginTimeout", "35");
myProp.put("ConnectionLoadBalance", "1");
Connection conn;
for (int x=1; x <= 4; x++) {
try {
System.out.print("Connect attempt #" + x + "...");
conn = DriverManager.getConnection(
"jdbc:vertica://node01.example.com:5433/vmart", myProp);
Statement stmt = conn.createStatement();
// Set the load balance policy to round robin before testing the database's load balancing.
stmt.execute("SELECT SET_LOAD_BALANCE_POLICY('ROUNDROBIN');");
// Query system to table to see what node we are connected to. Assume a single row
// in response set.
ResultSet rs = stmt.executeQuery("SELECT node_name FROM v_monitor.current_session;");
rs.next();
System.out.println("Connected to node " + rs.getString(1).trim());
conn.close();
} catch (SQLTransientConnectionException connException) {
// There was a potentially temporary network error
// Could automatically retry a number of times here, but
// instead just report error and exit.
System.out.print("Network connection issue: ");
System.out.print(connException.getMessage());
System.out.println(" Try again later!");
return;
} catch (SQLInvalidAuthorizationSpecException authException) {
// Either the username or password was wrong
System.out.print("Could not log into database: ");
System.out.print(authException.getMessage());
System.out.println(" Check the login credentials and try again.");
return;
} catch (SQLException e) {
// Catch-all for other exceptions
e.printStackTrace();
}
}
}
}
Running the above example produces the following output:
Connect attempt #1...Connected to node v_vmart_node0002 Connect attempt #2...Connected to node v_vmart_node0003 Connect attempt #3...Connected to node v_vmart_node0001 Connect attempt #4...Connected to node v_vmart_node0002