Without Application Continuity in place, database recovery does not mask outages to applications and end users.
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Restrictions and Other Considerations for Application ContinuityĪpplication Continuity attempts to mask many recoverable database outages (when replay is successful) from applications and users by restoring the database session: the full session, including all states, cursors, variables, and the last transaction if there is one.Īpplication Continuity addresses the problem that arises when an application is trying to access the database and the database session becomes unavailable due to an unplanned or planned outage (timeout, network outage, instance failure, repair, configuration change, patch apply, and so on). Potential Side Effects of Application Continuity This chapter assumes that you are familiar with the major relevant concepts and techniques of the technology or product environment in which you are using Application Continuity, such as Oracle WebLogic Server, Oracle RAC, or Oracle Active Data Guard (Oracle ADG).Īpplication Continuity Operation and Usage Introduced in Oracle Database 12 c Release 1 (12.1.0.1), Application Continuity strengthens the fault tolerance of systems and applications that use an Oracle database.Ĭurrently, the terms "Application Continuity" and the named feature "Application Continuity for Java" are synonymous, for purposes of this chapter. Recoverable errors when replay has encountered a restriction (see Section 26.4, "Restrictions and Other Considerations for Application Continuity"), such as use of concrete classes in the application, or when replay has not been able to restore the client-visible state to that on which the client may have made decisions so far. (Application Continuity applies only to recoverable errors.) Nonrecoverable errors, such as invalid input data. However, applications still must include error handling for these cases: If the request can continue, the database and the database session must be in the right state.Īpplication Continuity, however, does this work for the application developer, thus masking many outages in a safe way.Īpplication Continuity improves developer productivity by attempting to mask outages that can be masked. Nontransactional database session state that the application needs to operate is lost. If a COMMIT has been issued, the COMMIT message is not durable.Ĭhecking a lost request is no guarantee that it will not COMMIT after being checked. The state at the client remains at present time, with entered data, returned data, and variables cached.
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Without Application Continuity, it can be almost impossible for an application to mask outages in a safe way, for reasons that include the following: With Application Continuity, the end user experience is improved by masking many outages, planned and unplanned, without the application developer needing to attempt to recover the request. After a successful replay, the application can continue where that database session left off, instead of having users left in doubt not knowing what happened to their funds transfers, flight bookings, and so on, and avoiding the need to reboot mid-tier machines to recover from logon storms.
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The request can contain transactional and nontransactional work. Application Continuity is a feature that enables the replay, in a nondisruptive and rapid manner, of a request against the database after a recoverable error that makes the database session unavailable.