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Oracle Essentials: Oracle9i, Oracle8i and Oracle8, Second Edition by Jonathan Stern, Robert Stackowiak, Rick Greenwald

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Moving Data Between Distributed Systems

The previous section discussed the use of multiple database servers acting together as part of a single logical database for users. The following situations call for the contents of a database to be duplicated and moved between systems:

  • When data available locally eliminates network bandwidth issues or contention for system resources

  • When mobile database users can take their databases with them and operate disconnected from the network

  • When redundant databases can help to deliver higher levels of reliability, as each database can be used as a backup for other databases

The biggest issue facing users of multiple identical or similar databases is how to keep the data on all of the servers in sync as the data is changed over time. As a user inserts, updates, or deletes data on one database, you will need to find some way to get this new data to the other databases. In addition, you will have to deal with the possible data-integrity issues that can crop up if the changes introduced by distributed users contend with each other.

Oracle offers a number of strategies to address this situation. The following sections discuss techniques for data and table movement among distributed systems.

Advanced Replication

The copying and maintaining of database tables among multiple Oracle databases on distributed systems is known as replication. Changes that are applied at any local site are propagated automatically to all of the remote sites. These changes ...

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