Database system configured for automatic failover with no data loss
First Claim
1. An automatic failover configuration comprising:
- configuration participants including a primary database system that produces redo data, a standby database system that receives the redo data, and an observer;
a messaging system for sending and receiving messages among the participants, and in each participant, a copy of configuration state of the automatic failover configuration that specifies one of a plurality of configuration states, the messages being used to propagate a most recent configuration state among the participants.
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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.
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Citations
18 Claims
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1. An automatic failover configuration comprising:
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configuration participants including a primary database system that produces redo data, a standby database system that receives the redo data, and an observer;
a messaging system for sending and receiving messages among the participants, and in each participant, a copy of configuration state of the automatic failover configuration that specifies one of a plurality of configuration states, the messages being used to propagate a most recent configuration state among the participants. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14)
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15. A method of preventing automatic failover from resulting in divergence among database systems in an automatic failover configuration, the automatic failover configuration having
participants including a first database system, a second database system, and an observer, in each participant, a persistent copy of a configuration state value that specifies one of a plurality of configuration states of the automatic failover configuration and the method being performed during a transition from one of the plurality of configuration states to another thereof and, and having the steps performed in a participant of the participants of: -
determining that another participant has persisted the configuration state value for the other configuration state; and
thereupon persisting the configuration state value for the other configuration state. - View Dependent Claims (16, 17, 18)
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Specification