Database replication is the process of sharing data or database design changes between databases in different locations without having to copy the entire database. Replication involves copying a database so that two or more copies of a single database remain synchronized. The original database is called a Design Master and each copy of the database is called a replica. Together, the Design Master and the replicas make up a replica set. There is only one Design Master in a replica set. The Design Master is the only member of the replica set where you can make design changes to the objects in the database. Each member of the replica set contains a common set of replicable objects, such as tables, queries, forms, reports, macros, or modules. Each member of the replica set can also contain nonreplicated — or local — objects.
Synchronization is the process of ensuring that every copy of the database contains the same objects and data. When you synchronize the replicas in a replica set only the data that has changed is updated. You can also synchronize changes made to the design of the objects in the Design Master.
If you design your applications for multiple users, database replication, in the appropriate circumstances, can improve the way your users share data. By using database replication, you can make copies of a database so that two or more users can work on their own copy of the database at the same time and each user’s changes are passed on to other members of the replica set through synchronization.
Implementing Database Replication
Microsoft Jet Replication Architecture
Synchronization Conflicts and Errors
Advanced Design Considerations
You can use the code examples in this chapter to help you understand the concepts discussed, or you can modify them and use them in your own applications.
The code examples are located in the JetBook\Samples subfolder on the companion CD-ROM. The code examples for Microsoft Access 97 are in JetSamples.mdb, and the corresponding code examples for Microsoft Visual Basic version 5.0 and other applications that support Visual Basic for Applications are referenced in JetSamples.vbp. Both JetSamples.mdb and JetSamples.vbp use tables and queries in NorthwindTables.mdb, also located in the JetBook\Samples subfolder.
To use the code examples, copy the sample files to your hard disk. Be sure to copy NorthwindTables.mdb as well so that you can use the code examples to work with data.
The companion CD-ROM also includes three databases that you can use to study database replication. These samples are located in the JetBook\Samples\Replicas subfolder. The databases include SampleDesignMaster.mdb, the Design Master for the replica set; SampleReplica.mdb, a replica created from the Design Master; and SamplePartialReplica.mdb, a partial replica created from the Design Master.
See Also For more information about copying and using the code examples from the companion CD-ROM, see “Using the Companion CD-ROM” in the Preface.