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Sybase Enterprise Data Studio Feature Guide

Chapter 2: Enterprise Data Studio: The Building Blocks

Data Replication

Data Replication

In Enterprise Data Studio, Sybase offers two replication technologies: Replication Server and SQL Remote.

• Replication Server provides the robust, detailed replication required by complex, distributed enterprises where a high volume of replicated messages and heterogeneous architectures are common.
• SQL Remote delivers two-way replication between laptop or desktop computers and company databases. It brings replication to smaller enterprises and, when used with Replication Server, extends replication options at larger ones.

The functions and components described in this section are:

• Replication Server Technology - Replication Server and Replication Agent for Adaptive Server Anywhere
• SQL Remote Technology - SQL Remote

Replication Server Technology

Replication Server is an Open Server application that provides reliable, fast replication among databases on a network. It maintains data integrity and consistency across multiple databases and copies data to and from Adaptive Server and several non-Sybase, LAN-based and mainframe data servers.

Using Replication Server, you can ensure that users will always have access to data by creating a warm standby copy of critical databases. Then, should networks or systems fail, you can switch to the warm standby database with little or no interruption in service.

Replication Server uses a publish-and-subscribe model for replicating data across the network. Users "publish" data that is available in a primary database, and other users "subscribe" to the data for delivery in a replicate database. Users can replicate both data changes (update, insert, and delete operations) and stored procedures using this method.

Replicating tables on local data servers provides clients with local access to enterprise data, which results in improved performance and greater data availability.

Distributed database systems allow client applications to access data on multiple database servers throughout an enterprise¾even geographically dispersed enterprises. Replication Server ensures that data on replicate databases stays updated.

Replication Agents

Each site from which data is replicated (primary site) requires a replication agent. A replication agent captures transactions marked for replication and sends them to Replication Server for distribution.

As shown in Figure 2-8, Adaptive Server provides its own replication agent, RepAgent. RepAgent is an Adaptive Server thread that can be managed from Sybase Central.

Figure 2-8: RepAgent thread is part of Adaptive Server Enterprise

If you are replicating from a non-Sybase database, you must either install a Sybase replication agent that is specific for that database, or create such a replication agent. These replication agents are separate processes. See Figure 2-9.

Figure 2-9: Use a replication agent to replicate from a non-Sybase database

Enterprise Data Studio provides these standalone replication agents:

• Replication Agent for Adaptive Server Anywhere
• Replication Agent for Informix
• Replication Agent for Oracle

  Note: You can also use Replication Server to replicate data from DB2, IMS, and VSAM mainframe databases. Third-party replication agents for these databases are available from Sybase.

A Typical Installation

A typical installation (see Figure 2-10) may consist of many LANs and one or more WANs. Transactions marked for replication at the primary database are sent to the Replication Server. The Replication Server delivers the data to other Replication Servers or directly to subscribing databases.

Figure 2-10: A typical Replication Server replication system

Replicating Data Using Heterogeneous Data Servers

Replication Server supports heterogeneous data servers, allowing you to replicate data to and from both Sybase and non-Sybase data servers. Sybase open interoperability lets you:

• Replicate data using existing servers and databases without having to convert them
• Add data servers and databases as your enterprise grows and changes

To replicate data to and from heterogeneous data servers, you need:

• Data servers
• A replication agent for each database from which you replicate data
• A DirectConnect data access server for each database to which you replicate data
• Optionally, CIS (in Adaptive Server or OmniConnect) to perform datatype translations when replicating into Informix or Oracle databases. Include OmniConnect or Adaptive Server between Replication Server and DirectConnect.

Figure 2-11 shows an example of bidirectional replication using Replication Servers and heterogeneous data servers.

Figure 2-11: An example of bidirectional replication using non-Sybase data servers

SQL Remote Technology

SQL Remote brings two-way data replication to large numbers of databases on laptop or desktop computers. Using a laptop database, users can enter data locally while receiving updates from a corporate database that may be part of an enterprise replication system using Replication Server.

SQL Remote replication technology is message-based and requires no direct server-to-server connection¾occasional connections such as e-mail or a periodic dial-up link are sufficient. Each message carries its destination address so a direct connection is unnecessary. If your system allows it, you also can use file sharing as a simple method for replication.

Supported message systems are:

• SMTP/POP - Intranet e-mail protocol
• Microsoft Message Application Programming Interface (MAPI) - A message system used in Microsoft products and in cc:Mail release 8 and later
• Vendor Independent Messaging (VIM) - A message system used in Lotus Notes and some versions of Lotus cc:Mail.

SQL Remote is particularly economical with resources. In addition to a database¾Sybase Adaptive Server or Sybase Adaptive Server Anywhere¾the only software needed at each site is the SQL Remote Message Agent, which sends and receives the replication messages, and a message system. See Figure 2-12. If you use the file-sharing method, you do not need a Message Agent.

Figure 2-12: A typical SQL Remote replication system