In this article Barry Mavin, CEO and Chief Software Architect for Recital, details on how to use the Client Drivers provided with the Recital Database Server to work with local or remote server-side JDBC data sources.

Overview

The Recital Universal .NET Data Provider provides connectivity to the Recital Database Server running on any supported platform (Windows, Linux, Unix, OpenVMS) using the RecitalConnection object.

The Recital Universal JDBC Driver provides the same functionality for java applications.

The Recital Universal ODBC Driver provides the same functionality for applications that use ODBC.

Each of the above Client Drivers use a connection string to describe connections parameters.

The basic format of a connection string consists of a series of keyword/value pairs separated by semicolons. The equals sign (=) connects each keyword and its value.

The following table lists the valid names for keyword/values.

To connect to a server-side JDBC data source, you ue the gateway=value key/value pair in the following way.

gateway=jdbc:jdbc_driver_path_on_server;jdbc:Recital:args

You can find examples of connection strings for most ODBC and OLE DB data sources by clicking here.

Example in C# using the Recital Universal .NET Data Provider:

////////////////////////////////////////////////////////////////////////
// include the references below
using System.Data;
using Recital.Data;

////////////////////////////////////////////////////////////////////////
// The following code example creates an instance of a DataAdapter that 
// uses a Connection to the Recital Database Server, and a gateway to
// Recital Southwind database. It then populates a DataTable 
// in a DataSet with the list of customers via the JDBC driver. 
// The SQL statement and Connection arguments passed to the DataAdapter 
// constructor are used to create the SelectCommand property of the
// DataAdapter.
public DataSet SelectCustomers()
{
	string gateway = "jdbc:/usr/java/lib/RecitalJDBC/Recital/sql/RecitalDriver;"+
			"jdbc:Recital:Data Source=localhost;database=southwind";       
	RecitalConnection swindConn = new
			RecitalConnection("Data Source=localhost;gateway=\""+gateway+"\");
	RecitalCommand selectCMD = new
			RecitalCommand("SELECT CustomerID, CompanyName FROM Customers", swindConn);
	selectCMD.CommandTimeout = 30;
	RecitalDataAdapter custDA = new RecitalDataAdapter();    
	custDA.SelectCommand = selectCMD;    
	swindConn.Open();    
	DataSet custDS = new DataSet();
	custDA.Fill(custDS, "Customers");    
	swindConn.Close();
	return custDS;
}

Example in Java using the Recital Universal JDBC Driver:

////////////////////////////////////////////////////////////////////////
// standard imports required by the JDBC driver
import java.sql.*;
import java.io.*;
import java.net.URL;
import java.math.BigDecimal;
import Recital.sql.*;

////////////////////////////////////////////////////////////////////////
// The following code example creates a Connection to the Recital 
// Database Server, and a gateway to the Recital Southwind database. 
// It then retrieves all the customers via the JDBC driver.
public void SelectCustomers()
{
    // setup the Connection URL for JDBC
    String gateway = "jdbc:/usr/java/lib/RecitalJDBC/Recital/sql/RecitalDriver;"+
			"jdbc:Recital:Data Source=localhost;database=southwind";       
    String url = "jdbc:Recital:Data Source=localhost;gateway=\""+gateway+"\";

    // load the Recital Universal JDBC Driver
    new RecitalDriver();

    // create the connection
    Connection con = DriverManager.getConnection(url);

    // create the statement
    Statement stmt = con.createStatement();

    // perform the SQL query
    ResultSet rs = stmt.executeQuery("SELECT CustomerID, CompanyName FROM Customers");

    // fetch the data
    while (rs.next()) 
    {
        String CompanyID = rs.getString("CustomerID");
        String CompanyName = rs.getString("CompanyName");
        // do something with the data...
    }
    
    // Release the statement
    stmt.close();

    // Disconnect from the server
    con.close();
}

Occasionally as a Linux administrator you will be in the situation where working on a remote server and you are left with no option but to force a reboot the system. This may be for a number of reasons, but where I have found it most frequent is when working on Linux clusters in a remote location.

When the "reboot" or "shutdown" commands are executed daemons are gracefully stopped and storage volumes unmounted.
This is usually accomplished via scripts in the /etc/init.d directory which will wait for each daemon to shut down gracefully before proceeding on to the next one. This is where a situation can develop where your Linux server fails to shutdown cleanly leaving you unable to administer the system until it is inspected locally. This is obviously not ideal so the answer is to force a reboot on the system where you can guarantee that the system will power cycle and come back up. The method will not unmount file systems nor sync delayed disk writes, so use this at your own discretion.

To force the kernel to reboot the system we will be making use of the magic SysRq key.

The magic_SysRq_key provides a means to send low level instructions directly to the kernel via the /proc virtual file system.

To enable the use of  the magic SysRq option type the following at the command prompt:

    echo 1 > /proc/sys/kernel/sysrq

Then to reboot the machine simply enter the following:

    echo b > /proc/sysrq-trigger

Voilà! Your system will instantly reboot.
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MQCURMSGS()

Syntax

Description

Example

mqdes=mqopen("/myqueue")
if (mqdes < 0)
   messagebox(strerror()+",errno="+alltrim(str(error())))
   return
endif
do while (mqcurmsgs(mqdes) > 0)
   mstr=mqreceive(mqdes)
   if (empty(mstr))
      messagebox(strerror()+",errno="+alltrim(str(error())))
      return
   endif
   messagebox(mstr)
end do
mqclose(mqdes)