Oracle Distributed Systems

Chapter 11. Basic Replication

The origin of Oracle’s replication technology is the read-only snapshot feature, which shipped with the first Oracle7 release. Read-only snapshots, also known as basic replication, are essentially tables that hold the result set of a query on a remote database. We usually configure the snapshot to refresh the result set at a predetermined interval so that the data is current.

About Read-Only Snapshots

Read-only snapshots provide a means to access remote data without requiring a constant network connection. They are intended to maintain local instances of data that the remote master site maintains.

Examples of the appropriate use of read-only snapshots include the following:

• A regional sales office has a snapshot of the PRODUCT_PRICES table which the headquarters site maintains. The snapshot is refreshed once a month, when prices change.

• A retailer’s data warehouse performs a snapshot of the DAILY_REGISTER_RECEIPTS table as part of the nightly data extraction process.

• A billing system performs a snapshot of the CUSTOMER_ADDRESS table prior to each invoice run so that the bills are mailed to the correct addresses.

• A salesperson with a laptop connects to the master sales database and refreshes a snapshot of the subset of the CUSTOMER_LEAD table corresponding to her sales region.

Notice that in each case the snapshot is refreshed at an interval that ensures accurate business processing and that the master site “owns” the data—that is, only the master site can ...