Introducing DataExchange
Understanding DataExchange and Its Capabilities
The following topics introduce you to DataExchange, its editions, and its components:
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DataExchange Technical Overview
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DataExchange Editions
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DataExchange Components
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Where to Install DataExchange
DataExchange Technical Overview
DataExchange is the PSQL database replication solution. It copies data between two or more PSQL databases to maintain warm backup systems, drive data into reporting servers, or synchronize multiple remote databases.
The DataExchange technology works by capturing and sharing changes from one PSQL database to other databases in a DataExchange replication network. The PSQL Engine is augmented with DataExchange, which adds two software components to a PSQL database, the Replication Event Handler and the replication engine.
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The Replication Event Handler (REH) plugs directly into the PSQL database engine. Specifically, the REH is a set of DLLs that operate within the database engine, so if the database is running, the replication event handler is running as well. The database engine activates the REH when there is a change event (insert, update, delete). The REH then makes note of the event in one of its private control tables.
Note The Replication Event Handler is available for both 32 and 64-bit platforms.
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The replication engine is a separate process that performs the actual replication task. It reads the control tables to determine what records have changed since the last replication session. It then groups these changes into packets and shares them with the other replication engines participating in a DataExchange replication network. These other engines then apply the updates to their own databases. The replication process occurs either continuously, at scheduled intervals, or on demand. The replication engine does not require constant network connectivity, so DataExchange is suitable for scenarios with intermittent connectivity, like remote users with dialup connections.
DataExchange focuses on the two types of data replication:
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Providing continuous access to data (Real-Time Backup)
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Synchronizing multiple databases (Data Synchronization)
While both capabilities are useful, one typically surfaces as the primary driver for implementing data replication technology in a specific environment.
Notification Agent
The notification agent, or agent for short, is another component installed by DataExchange. Its purpose is to send email if a replication failure occurs. The agent requires the basic Simple Mail Transfer Protocol (SMTP) to communicate with a mail server.
Note that the agent is installed only if the machine contains the PSQL Server product. The agent is not available if you install DataExchange on a machine with the PSQL Workgroup product.
For more information, see dxagent.
Replication-Specific Files
DataExchange adds its own tables on the machine where replication executes. It uses two types of tables: system configuration and replication control. Configuration tables record information such as the databases being replicated, the sites to which data is replicated, and replication schedules.
Control tables shadow data files and track the replication state of each record in the data. Each data table or file has a control table counterpart. Similarly, each data record has a companion control table record. Through the control tables, the replication engine determines what records need to be replicated when.
DataExchange tables for replication configuration and control can reside with the files to be replicated or separately in their own database. The choice of location depends on your replication needs.
DataExchange Editions
DataExchange is available in two editions: Real-Time Backup and Data Synchronization. The following table compares the two editions.
Feature
Edition
 
Real-Time Backup
Data Synchronization
1-way replication
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2-way replication
 
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Real-Time Backup Edition
DataExchange Real-Time Backup Edition is optimized for maintaining a backup server. It pairs high performance with minimal installation and maintenance. This edition supports 1-way replication between a primary server and a backup server.
Real-Time Backup solutions can be on-site or off-site, depending on your needs. Onsite backups ensure your data is protected from hardware failures. Protecting your data means that data recovery time is reduced and downtime is minimal. Solutions that implement an offsite backup server gain protection to your data against catastrophic loss, such as fire, flood or theft.
Data Synchronization Edition
DataExchange Data Synchronization Edition is optimized for more complex replication scenarios. This edition supports multiple participating databases and data flowing in multiple directions.
The real-time data replication offered in Data Synchronization ensures all users see the same up-to-the-minute information. The ability to configure flexible topologies allows data flows to match the business organization.
DataExchange Components
DataExchange consists of the following primary components:
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Replication engine – Used for distributing and applying captured database changes
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Replication Event Handler (REH) – Used for recording or monitoring database change events
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DataExchange Agent – Used to provide notification in the event of a replication failure
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DataExchange utilities – Used to perform the tasks necessary for replication, such as design and activation
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DataExchange documentation – Provides concepts, instructions, and examples
DataExchange Utilities
DataExchange utilities help you configure and manage the replication process.
Utility Name
Capabilities
Deployment Wizard
Set up a replication network between a First Site and one or more Partner Sites. For examples of its use, see Replication Deployment.
Manager
Set up replication schedules and control user access.
Monitoring tool
Monitor data replication, configure replication sessions, and set logging options.
Activation tool
Enable a database to participate in replication and establish the database as belonging to a site on the replication network.
Deactivation tool
Remove a database from the list of those available for replication. If you want to delete a replicated database from physical storage, you must deactivate it first.
For more information, see Using the DataExchange Utilities and Services.
Documentation
DataExchange User's Guide includes conceptual and procedural information related to installation and configuration and design and deployment of a replication network. This guide covers both the Real-Time Backup and the Data Synchronization editions of the product. Many procedures for the two editions are identical or nearly so. Where differences occur, they are noted for your particular edition.
Where to Install DataExchange
DataExchange must be installed on the same computer as the PSQL Server, Vx Server, or Workgroup engine. See also Preparing to Install DataExchange.