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.

Name	Default	Description
Data Source -or- Server -or-Nodename		The name or network address of the instance of the Recital Database Server which to connect to.
Directory		The target directory on the remote server where data to be accessed resides. This is ignored when a Database is specified.
Encrypt -or- Encryption	false	When true, DES3 encryption is used for all data sent between the client and server.
Initial Catalog -or- Database		The name of the database on the remote server.
Password -or- Pwd		The password used to authenticate access to the remote server.
User ID		The user name used to authenticate access to the remote server.
Connection Pooling -or- Pool	false	Enable connection pooling to the server. This provides for one connection to be shared.
Logging	false	Provides for the ability to log all server requests for debugging purposes
Rowid	true	When Rowid is true (the default) a column will be post-fixed to each SELECT query that is a unique row identifier. This is used to provide optimised UPDATE and DELETE operations. If you use the RecitalSqlGrid, RecitalSqlForm, or RecitalSqlGridForm components then this column is not visible but is used to handle updates to the underlying data source.
Logfile		The name of the logfile for logging
Gateway		Opens an SQL gateway(Connection) to a foreign SQL data source on the remote server. Using Gateways, you can transparently access the following local or remote data sources: Recital Oracle ODBC (Server-side ODBC data sources) JDBC (Server-side JDBC data sources) ADO (Use this to connect to SQL Server and other Native Windows OLEDB data sources) MySQL PostgreSQL The gateway can be specified in several formats: servertype@nodename:username/password-database e.g. oracle@nodename:username/password-database mysql@nodename:username/password-database postgresql@nodename:username/password-database -or- odbc:odbc_data_source_name_on_server oledb:oledb_connection_string_on_server jdbc:jdbc_driver_path_on_server;jdbc:Recital:args

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();
}

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DRBD:
DRBD (Distributed Replicated Block Device) forms the storage redundancy portition of a HA cluster setup. Explained in basic terms DRBD provides a means of achieving RAID 1 behavoir over a network, where whole block devices are mirrored accross the network.

To start off you will need 2 indentically sized raw drives or partitions. Many how-to's on the internet assume the use of whole drives, of course this will be better performance, but if you are simply getting familar with the technology you can repartition existing drives to allow for two eqaully sized raw partitions, one on each of the systems you will be using.

There are 3 DRBD replication modes:
• Protocol A: Write I/O is reported as completed as soon as it reached local disk and local TCP send buffer
• Protocol B: Write I/O is reported as completed as soon as it reached local disk and remote TCP buffer cache
• Protocol C: Write I/O is reported as completed as soon as it reached both local and remote disks.

If we were installing the HA cluster on a slow LAN or if the geogrphical seperation of the systems involved was great, then I recommend you opt for asyncronous mirroring (Protocol A) where the notifcation of a completed write operation occurs as soon as the local disk write is performed. This will greatly improve performance.

As we are setting up our HA cluster connected via a fast LAN, we will be using DRBD in fully syncronous mode, protocol C.
Protocol C involves the file system on the active node only being notified that the write operation was finished when the block is written to both disks of the cluster. Protocol C is the most commonly used mode of DRBD.

/etc/drbd.conf

global { usage-count yes; }
common { syncer { rate 10M; } }
resource r0 {
protocol C;
net {
max-buffers 2048;
ko-count 4;
}
on bailey {
device    /dev/drbd0;
disk      /dev/sda4;
address   192.168.1.125:7789;
meta-disk internal;
}
on giskard {
device    /dev/drbd0;
disk      /dev/sda3;
address   192.168.1.127:7789;
meta-disk internal;
}
}

drbd.conf explained:

Global section, usage-count. The DRBD project keeps statistics about the usage of DRBD versions. They do this by contacting a HTTP server each time a new DRBD version is installed on a system. This can be disabled by setting usage-count no;.

The common seciton contains configurations inhereted by all resources defined.
Setting the syncronisation rate, this is accoimplished by going to the syncer section and then assigning a value to the rate setting. The syncronisation rate refers to rate in which the data is being mirrored in the background. The best setting for the syncronsation rate is related to the speed of the network with which the DRBD systems are communicating on. 100Mbps ethernet supports around 12MBps, Giggabit ethernet somewhere around 125MBps.

in the configuration above, we have a resource defined as r0, the nodes are configured in the "on" host subsections.
"Device" configures the path of the logical block device that will be created by DRBD
"Disk" configures the block device that will be used to store the data.
"Address" configures the IP address and port number of the host that will hold this DRBD device.
"Meta-disk" configures the location where the metadata about the DRBD device will be stored.
You can set this to internal and DRBD will use the physical block device to store the information, by recording the metadata within the last sections of the disk.
Once you have created your configuration file, you must conduct the following steps on both the nodes.

Create device metadata.

$ drbdadm create-md r0
v08 Magic number not found
Writing meta data...
initialising activity log
NOT initialized bitmap
New drbd meta data block sucessfully created.
success

Attach the backing device.
$ drbdadm attach r0

Set the syncronisation parameters.
$ drbdadm syncer r0

Connect it to the peer.
$ drbdadm connect r0

Run the service.
$ service drbd start

Heartbeat:

Heartbeat provides the IP redundancy and the service HA functionailty.
On the failure of the primary node the VIP is assigned to the secondary node and the services configured to be HA are started on the secondary node.

Heartbeat configuration:

/etc/ha/ha.conf

## /etc/ha.d/ha.cf on node1
## This configuration is to be the same on both machines
## This example is made for version 2, comment out crm if using version 1
// replace the node variables with the names of your nodes.

crm no
keepalive 1
deadtime 5
warntime 3
initdead 20
bcast eth0
auto_failback yes
node bailey
node giskard

/etc/ha.d/authkeys
// The configuration below set authentication off, and encryption off for the authentication of nodes and their packets.
//Note make sure the authkeys file has the correct permisisions chmod 600

## /etc/ha.d/authkeys
auth 1
1 crc

/etc/ha.d/haresources
//192.168.1.40 is the VIP (Virtual IP) assigned to the cluster.
//the "smb" in the configuration line represents the service we wish to make HA
// /devdrbd0 represents the resource name you configured in the drbd.conf

## /etc/ha.d/haresources
## This configuration is to be the same on both nodes

bailey 192.168.1.40 drbddisk Filesystem::/dev/drbd0::/drbdData::ext3 smb

This article examines the advantages of using databases and looks at how to create databases for new and existing applications.

Overview

file which contains information, including full path details, about all the files that belong to that particular database. Opening a database gives an application access to all that database's files - operating system and data dictionary protection and security permitting - in whichever directory on the system they reside and database commands can target the files as a single unit.

NOTE: The word 'database' has often been used in Xbase products to refer to an individual '.dbf' file. In this article these are referred to as 'tables' and a database may contain many tables.

Advantages

Recital has always offered developers the maximum in flexibility in the design and deployment of their applications. The SET DEFAULT and SET PATH commands along with the ability to access files via their full Operating System path name has allowed data and code to be created and stored in any required location. Such flexibility does however put the onus on the developer to manage all elements of the application and ensure that maintenance tasks cover all files. The introduction of the database commands retains the established developer-driven design, but provides functionality to facilitate the access and maintenance of the components of that design. The functionality offered is in three main areas:

• Facilitate data access
• Facilitate the storage and extraction of information about the files in an application
• Facilitate the maintenance of the files in an application

These three areas are looked at in more detail in the sections below.

Data Access

The immediate effect of using a database is that all the database's tables and associated files (indexes, dictionaries, memo files) are accessible with the issue of a single command, the OPEN DATABASE command.

// Open the database
> open database southwind
// List the database tables
> list tables

Tables in Database southwind:
 Name                Source
 categories		/usr/recital/data/southwind/categories.dbf
 customers		/usr/recital/data/southwind/customers.dbf
 employees		/usr/recital/data/southwind/employees.dbf
 example		/usr/recital/data/southwind/example.dbf
 order_details	/usr/recital/data/southwind/order_details.dbf
 orders			/usr/recital/data/southwind/orders.dbf
 productsbyname	/usr/recital/data/southwind/productsbyname.dbf
 products		/usr/recital/data/southwind/products.dbf
 shippers		/usr/recital/data/southwind/shippers.dbf
 suppliers		/usr/recital/data/southwind/suppliers.dbf
 cisamdemo		/usr/recital/data/southwind/cisamdemo.dbf

> use example

In the case of the sample southwind database that ships with Recital products on all platforms and is shown above, this effect can be achieved in other ways (SET PATH or SET DEFAULT), since its files all reside in the southwind directory. The database advantage comes when the database catalog contains files from multiple directories, e.g.

// Open the database
> open database myapp
// List the database tables
> list tables

Tables in Database myapp:
  Name                Source
  zipcodes		/usr/myapp/data/lookups/zipcodes.dbf
  customers		/usr/myapp/data/current/customers.dbf
  archive03		/usr/myapp/data/archive/archive03.dbf
  archive04		/usr/myapp/data/archive/archive04.dbf
  users			/usr/allapps/data/users.dbf
  menus		/usr/myapp/data/system/menus.dbf

// Open a table
> use users

The OPEN DATABASE command requires only the database name to be specified, not the complete path of a directory as with SET PATH or SET DEFAULT. Databases are searched for in the sub-directories of the directory defined in the DB_DATADIR environment variable or symbol. DB_DATADIR is set in the system wide configuration file.

#---------------------------------------------------
# location of directories and important files
#---------------------------------------------------
DB_DATADIR="${ROI_ROOT}data/"     ;export DB_DATADIR

NOTE: DB_DATADIR is read from these files at startup to determine the home directory for databases. Updates to DB_DATADIR once a Recital process is running do not change this setting. The OPEN DATABASE command and certain other database commands allow a '?' to be specified in place of a database name. In this case the 'Select a file' dialog is displayed, listing the available files in the DB_DATADIR directory.

Click image to display full size

Fig 1: Recital Terminal Developer OPEN DATABASE ? command.

This functionality is also supported by the PACK DATABASE, REBUILD DATABASE and REINDEX DATABASE commands.

Databases can also simplify data access for Recital Client Drivers using the Recital Database Server: instead of specifying a starting directory, only a database name is required. The database can handle files from multiple directories and associate tables with their single index files.

Recital Universal .NET Data Provider

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

/////////////////////////////////////////
// sample code to call a Stored Procedure
public int CallStoredProcedure()
{
    string source = "Data Source=localhost;" +
	                "Database=southwind;" +
			"uid=?;"+
			"pwd=?";
						
	RecitalConnection conn = new RecitalConnection(source);
	...

Recital Universal JDBC Driver

import java.sql.*;
import java.io.*;
import java.net.URL;
import java.math.BigDecimal;
import Recital.sql.*;

public class jdbc_test {

  public static void main(String argv[]) {
    int i;
    ResultSet rs;
    ResultSetMetaData rsmd;

    System.out.println("Recital JDBC driver verification.");
	
    for (int ii=0; ii<1; ++ii) {
      try {
        //----------------------------------------------------------
        //-- Load the Client Driver for the
        //-- Recital Universal Application Server
        //----------------------------------------------------------
        System.out.println("Loading Recital JDBC driver.");
        new RecitalDriver();
        //-----------------------------------------------------------
        //-- The standard format of the connection URL is as follows:
        //-----------------------------------------------------------
        String url = "jdbc:Recital:" +
                     "SERVERNAME=?;" +
                     "DATABASE=jdbc_test;" +
                     "USERNAME=?;" +
                     "PASSWORD=?;" +
                     "ENCRYPTION=false";
...

Windows Recital Universal ODBC Driver

Click image to display full size

Fig 2: Recital Universal ODBC Driver DSN setup using a database.

Database Procedure Libraries

A database can have an associated procedure library, which is automatically opened when the database is opened. This way, any procedures required by the database's data files are always available. The procedure library should reside in the database's directory and be named dbc_xxx_library.prg, where 'xxx' is the name of the database. When the OPEN DATABASE command is issued, a check is made for the database procedure library and a SET PROCEDURE TO dbc_xxx_library.prg ADDITIVE issued automatically. The procedure library is in turn closed when the CLOSE DATABASES command is issued. This is particularly convenient for client/server database access.

Database Events

Issuing the OPEN DATABASE or CLOSE DATABASES command also fires a database event. Database events, like triggers for tables and forms, can have programs associated with them. The OPEN DATABASE command fires the DBC_OPENDATA event and will run a program called db_opendata.prg if one exists in the database's directory. Similarly, the CLOSE DATABASES command fires the DBC_CLOSEDATA event and runs the db_closedata.prg program. Both of these events also allow the current open or close operation to be abandoned if the associated program returns a logical false (.F.).

Information

Databases, specifically database catalogs, are an excellent place to store information about the files required by a particular application. Instead of having to search through application code to determine which tables are being used and what index keys they have, this information can be viewed in the database catalog. Database catalogs are themselves Recital tables and can be viewed and/or updated in the same way as any other Recital table. There is also a series of commands to provide information about the currently open database. DISPLAY/LIST DATABASE The DISPLAY DATABASE and LIST DATABASE commands display the database name and path, followed by the equivalent of LIST STRUCTURE INDEX and LIST DICTIONARY for each table in the database, e.g.

> open database southwind
> display database

Database Name:  southwind
Database Path:  /usr/recital-9.0/data/southwind/

Structure for database : categories.dbf
Number of data records : 8
Date of creation : 05/12/2004
Date of last update : 05/12/2004
Database encrypted : False


Field	Field Name		Type			Width	Dec	Description
    1	CATEGORYID	Numeric       	10			Category ID
    2	CATEGORYNAME	Character     	15			Category Name
    3	DESCRIPTION	Memo           	8			Description
    4	PICTURE		Memo           	8			Picture
** Total **                       42
Production DBX file: categories.dbx
  Master Index TAG: CATEGORYID
  Key: categoryid
  Type: Binary
  Len: 8
...

DISPLAY DATABASE shows the data one screen at a time, whereas LIST DATABASE is ideal for output to a file.

> open database southwind
> list database to file info.txt

DISPLAY/LIST TABLES

LIST TABLES, as we have seen above, lists all the tables from the database, giving each table's name and path. DISPLAY TABLES shows the information one screen at a time.

Maintenance

Using a database can simplify the maintenance of an application's programs, tables and indexes. Multiple files, possibly in different directories, can be targeted by a single database command.

COMPILE DATABASE

The COMPILE DATABASE command can be used to issue a COMPILE command for all program files listed in the database catalog.

// Open the database
open database myapp

// Compile all the database's programs
compile database

NOTE: Program files are added to a database using the SQL CREATE PROCEDURE command.

PACK DATABASE

The PACK DATABASE command issues a PACK command for every table in the database catalog. The PACK command is used to permanently remove any records that have been marked for deletion using the DELETE command.

// Open the database
open database southwind
// Pack all the database's tables
pack database

REINDEX DATABASE

The REINDEX DATABASE command rebuilds all the tag and single indexes in the catalog. This is the equivalent of an INDEX ON <key> TO | TAG <index> for each catalogued index key.

// Open the database
open database southwind
// Rebuild all the database's indexes
reindex database

NOTE: Using a database helps protect against a table being opened without its associated single index files also being opened. Any single index files that are included in the database catalog will automatically be opened when their table is opened via the database. If a single index appears in the database catalog, but the physical file no longer exists, it will be removed from the catalog when its associated table is next opened. All indexes, tagged indexes or single indexes, created while the database is open, are added automatically to the database catalog.

REBUILD DATABASE

The REBUILD DATABASE command is used to PACK, rebuild the index tags and refresh the contents of the database catalog file.

// Rebuild the database
rebuild database southwind

Creating and populating a database

Databases are created using the CREATE DATABASE command.

// Create new database
create database newdb

The CREATE DATABASE creates a sub-directory in the DB_DATADIR and initializes the new database's catalog file. The catalog file is given the same basename as the database and is a Recital table with a '.cat' file extension. It has a production index file with a '.cax' file extension and a memo file with a '.cam' file extension.

// Open the database
open database newdb

With the database open, the catalog file table is opened in the highest available workarea and is given an alias name of its basename preceded by an underscore, e.g. '_newdb'. Any new tables or indexes that are created will be automatically added into the catalog and form part of the database. 'Free' tables can also be manually added into a database using the SQL ADD TABLE command.

// config.db
set sql on
set sql to vfp
// end of config.db

// Create a 'free' table, with no database open
create table free1 (field1 char(10), field2 date)
// Open the database
open database newdb
add table free1

As the application runs, 'myapp' in the example above, each table that is opened is added to the database catalog. Indexes that are opened are added in the same way. Using SET AUTOCATALOG OFF, inclusion in the catalog can be restricted. Once all required areas of the application have been catalogued, the application can be updated to make use of the database commands.

Converting an existing application

The AUTOCATALOG commands can be used to automatically create a database catalog based on an existing application. The SET AUTOCATALOG TO >database< command will create the database if it does not already exist.

// Database must be closed during autocatalog process
close databases
// Specify the database
set autocatalog to myappdb
// Start the autocatalog process
set autocatalog on
do myapp
// The autocatalog process can be toggled off to exclude 
// certain parts of the application if required
// set autocatalog off

Exporting a database

The BACKUP DATABASE and RESTORE DATABASE commands have been added to simplify the process of moving applications between binary incompatible platforms. Binary files such as tables, memo files and data dictionaries must be exported to ASCII format to allow them to be transferred from one platform to another where the platforms have different binary ordering. For example, this is the case when moving files between a SUN Sparc Solaris machine and an Intel Linux machine. The BACKUP DATABASE and RESTORE DATABASE commands are extensions of the BUILD and INSTALL commands: where BUILD and INSTALL operate on a specified list of tables, BACKUP DATABASE and RESTORE DATABASE automatically handle an entire database.

// Open the database
open database southwind
// Export the database to ASCII format
backup database

The BACKUP DATABASE command goes through the database catalog, exporting each file into an ASCII format that can be handled by the RESTORE DATABASE command. The files are created in a directory with the same name as the database. This directory is a sub-directory of the directory specified in the environment variable DB_BACKUPDIR and is created automatically. By default, DB_BACKUPDIR is the 'backup' sub-directory of the Recital home directory.

// Query the DB_BACKUPDIR environment variable setting
> ? getenv([DB_BACKUPDIR])
/usr/recital/backup

Like DB_DATADIR, DB_BACKUPDIR is set in the system-wide configuration file and is read at startup to determine the home directory for database backups. Updates to DB_BACKUPDIR once a Recital process is running do not change this setting.

# profile.db/uas extract
#---------------------------------------------------
# location of directories and important files
#---------------------------------------------------
DB_BACKUPDIR="${ROI_ROOT}backup/"     ;export DB_BACKUPDIR

Once the BACKUP DATABASE command has completed, the files can be transferred to another platform, for example from Intel SCO OpenServer to IBM AIX and the RESTORE DATABASE command used to recreate the database.

// Export the database to ASCII format
// Note: the BACKUP DATABASE command operates
// on the active or specified database
$ db
> backup database southwind
> quit

// 'tar' up the files for transfer
$ cd /usr/recital/backup
$ tar cvf southwind.tar ./southwind

// Transfer the tar archive to DB_BAKUPDIR on the 
// target machine, then extract the files
$ pwd
/usr/recital/backup
$ tar xvf southwind.tar

// Rebuild the database on the target platform
// The database is automatically created 
// as a sub-directory of DB_DATADIR
$ db
> restore database southwind