In this article Barry Mavin, CEO and Chief Software Architect for Recital, details how to use the Client Drivers provided with the Recital Database Server to work with local or remote server-side OLE DB 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 equal sign (=) connects each keyword and its value.

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

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

gateway=oledb:oledb_connection_string_on_server

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
// the SQL server Northwind database. It then populates a DataTable 
// in a DataSet with the list of customers. 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 = "oledb:Provider=sqloledb;Initial Catalog=Northwind;
		Data Source=localhost;Integrated Security=SSPI";
	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 SQL server Northwind database. 
// It then retrieves all the customers.
public void SelectCustomers()
{
    // setup the Connection URL for JDBC
	String gateway = "oledb:Provider=sqloledb;Initial Catalog=Northwind;
		Data Source=localhost;Integrated Security=SSPI";
	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();
}

If when your attempt to create device meta-data fails this is drbd preventing you from corrupting a file system present on the target partition.

$ drbdadm create-md drbd0

v08 Magic number not found
md_offset 30005817344
al_offset 30005784576
bm_offset 30004867072

Found ext2 filesystem which uses 190804004 kB
current configuration leaves usable 29301628 kB

Device size would be truncated, which
would corrupt data and result in
'access beyond end of device' errors.
You need to either
 * use external meta data (recommended)
 * shrink that filesystem first
 * zero out the device (destroy the filesystem)
Operation refused.

Command 'drbdmeta /dev/drbd0 v08 /dev/sda4 internal create-md' terminated with exit code 40
drbdadm aborting

Once you have confirmed that the file system present on the target partition is no longer required at the prompt type the following:

Replace /dev/sdaX with the block device you are targeting.

dd if=/dev/zero of=/dev/sdaX bs=1M count=128

Once this has completed the drbdadm create-md drbd0 command will complete with a "success."

$ drbdadm create-md drbd0
v08 Magic number not found
v07 Magic number not found
v07 Magic number not found
v08 Magic number not found
Writing meta data...
initialising activity log
NOT initialized bitmap
New drbd meta data block successfully created.
success
$

VMware products, such as ESX, Workstation, Server, and Fusion, come with a built-in VNC server to access guests.

This allows you to connect to the guest without having a VNC server installed in the guest - useful if a server doesn't exist for the guest or if you need access some time when a server would not work (say during the boot process). It's also good in conjunction with Headless Mode.

The VNC server is set up on a per-VM basis, and is disabled by default. To enable it, add the following lines to the .vmx:

RemoteDisplay.vnc.enabled = "TRUE" 
RemoteDisplay.vnc.port = "5901"

You can set a password with RemoteDisplay.vnc.key; details for how to calculate the obfuscated value given a plaintext password are in Compute hashed password for use with RemoteDisplay.vnc.key.

If you want more than one VM set up in this manner, make sure they have unique port numbers. To connect, use a VNC client pointing at host-ip-address:port. If you connect from a different computer, you may have to open a hole in the OS X firewall. If you use Leopard's Screen Sharing.app on the same computer as Fusion, don't use port 5900 since Screen Sharing refuses to connect to that.

try
  open database southwind
catch
  die("Cannot open database, please try later.")
endtry