If you are still considering the use of TP monitors, you likely have one of these scenarios:
• Migration of legacy applications (usually originally written using CICS and COBOL for a mainframe) to CICS on Unix or Windows NT
• When mobile database users can take their databases with them and operate dis- connected 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 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 can include updates to data or changes to the database schema. Replication is frequently implemented to provide faster access for local users at remote sites or to provide a disaster-recovery site in the event of loss of a primary site. Oracle’s Advanced Repli-cation features support both asynchronous replication and synchronous replication. Oracle also supports heterogeneous replication to DB2 through its Replication Ser-vices, bundled in the Mainframe Integration Gateways.
Conflicts can occur when more than one site updates the same data element during the same replication interval. Changes are propagated using deferred remote proce-dure calls (RPCs) based on events or at points in time when connectivity is available or communications costs are minimal.
Several conflict-resolution routines provided with Enterprise Edition can be automat-ically used to resolve replication conflicts. An administrator can simply choose which conflict-resolution strategy he wishes to use for a particular replication. For updates that may affect a column or groups of columns, standard resolution choices include the following:
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