Production redeployment is a facility in WebLogic that provides the ability to temporarily have multiple versions of the same web application of web service active at the same time.  

Sometimes, changes in application functionality require redeployment of the application. In the theoretical case of instantaneous responses from applications, we could argue that the roll out of a new version of an application is akin to the flip-of-the-switch: request A is handled by version X, the switch is flipped to bring version X+1 live and the next request B is taken care of by the new version. This, however, is not the reality. Requests take longer to process than no time at all. Besides, requests live in the context of a session – this applies to database as well as application server. This means that replacing version X with a new version X+1 in a throw-the-switch manner would not only potentially interrupt pending non-zero duration requests but would also – and far more harmfully – destroy all pending sessions. This would definitely not constitute zero-downtime application upgrade.

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