Abstract: Techniques used in an automatic failover configuration having a primary database system, a standby database system, and an observer for preventing divergence among the primary and standby database systems while increasing the availability of the primary database system. In the automatic failover configuration, the primary database system remains available even in the absence of both the standby and the observer as long as the standby and the observer become absent sequentially. The failover configuration further permits automatic failover only when the observer is present and the standby and the primary are synchronized and inhibits state changes during failover. The database systems and the observer have copies of failover configuration state and the techniques include techniques for propagating the most recent version of the state among the databases and the observer and techniques for using carefully-ordered writes to ensure that state changes are propagated in a fashion which prevents divergence.

Abstract: A system, method, and computer program product communicate data dictionary information of database objects through a redo stream in the form of metadata, which provides the association between the internal numbers used by a database schema to identify database objects and the corresponding user-defined names of the database objects, in the redo stream itself, so that the association information may be easily and quickly used in the analysis of the redo stream of the database transactions. A method of communicating data dictionary information of database objects through a redo stream comprises the steps of performing a change to a first database data table, logging redo information representing the change to the first database data table to a redo stream, and logging information relating to internal identifier mapping information associated with the first database data table to the redo stream.

Abstract: The present invention is directed to a method and mechanism for encoding multiple virtual tables into one or more source tables. An aspect of the invention is directed to the access of a virtual table virtual table without requiring separate entries for the virtual table in the meta-data of a database system. Another aspect of the invention is directed to a virtual table that has different column signatures than its underlying source table(s).

Abstract: A method of change data captured is disclosed, in which modifications made to on-line transaction processing (OLTP) tables (e.g. inserts, updates, and deletes) are maintained in a database object, referred to as a change table. The change data in the change table is then made available to analysis applications in a controlled manner, such as in accordance with a publication-subscription model.

Abstract: A method of logical database snapshot for log-based replication in described that need not incur a quiescence of an operational database. Baselines for the overall snapshot operation and for each table replication are recorded in such a way that subsequent log-based replication can distinguish which redo records to apply and which to discard. The baselines may be recorded as system change numbers negotiated according to a distributed protocol for synchronizing a sequence number, and records from the redo log are applied on the logical standby system based on the recorded system change numbers.