The Oracle Replication Server

Alan Downing

Oracle Corporation

Abstract

Although a research topic since the early 80's, only recently have commercial database companies released asynchronous replication products. This talk overviews the architecture and capabilities of Oracle's asynchronous replication facilities including peer-to-peer row-level replication, master-slave snapshot replication, and procedural replication. Oracle's asynchronous replication provides immediate, local access to data, and allows systems to function autonomously even when the network or other systems in the distributed environment fail. Oracle's peer-to-peer replication facilitates a variety of replication models including primary site ownership of data, dynamic ownership of data, and shared ownership of data. Shared ownership of data is supported by automatic detection of conflicting updates and by invoking application-level conflict resolution routines. Oracle's architecture uses PL/SQL stored procedures, triggers, and "deferred" remote procedure calls. While peer-to-peer replication supports only full-table replication, snapshot replication allows subsets of master tables to be replicated. With masters able to resolve conflicts, updatable snapshots can update their local copies and then asynchronously propagate their updates to the master when the snapshots are refreshed. Because a set of snapshots can be consistently refreshed, referential integrity constraints can be maintained across master tables. Procedural replication allows calls to remote procedures to be queued and asynchronously invoked. Procedural replication allows efficient replication of bulk updates.