Oracle Distributed Systems

Types of Replication

No single replication methodology can meet all of the various business requirements listed earlier. Oracle’s four basic types of replication are described in Table 9.1.

Table 9-1. Types of Replication

Replication Type	Description	Example
Read-only snapshots	A master table is copied to one or more databases. Changes in the master table are reflected in the snapshot tables whenever the snapshot refreshes. The snapshot site determines the frequency of the refreshes; data is pulled.	A company may maintain its master product price list in a table at headquarters; regional sales offices or retail sites each have a snapshot of the price list in their local databases.
Updateable snapshots	Similar to read-only snapshots, except that the snapshot sites are able to modify the data and send their changes back to the master. The snapshot site determines the frequency of the refreshes and the frequency with which updates are sent back to the master.	A table of customer leads resides at headquarters. Sales staff with laptop computers visit prospective clients and enter notes about their meetings. When the sales staff dials in to the headquarters database every evening, their notes are uploaded, and they receive any updates that may have occurred since their last data refresh.
Multi-master replication	A table is copied to one or more databases, and each database has the ability to insert, update, or delete records from it. Modifications are pushed to the other database at an interval ...