Caching

The Caching pattern describes how to avoid expensive reacquisition of resources by not releasing the resources immediately after their use. The resources retain their identity, are kept in some fast-access storage, and are re-used to avoid having to acquire them again. Note: This pattern appeared in a heavily reworked and updated version in the book Pattern-Oriented Software Architecture — Patterns for Resource Management published by Wiley [POSA3]. Example Consider a network management system (NMS) that needs to monitor the state of many network elements (NEs). The NMS is typically implemented as a three-tier system. End-users interact with the system using the presentation layer-typically a GUI. The middle-tier comprising the business logic interacts with the persistence layer and is also responsible for communicating with the physical NEs. Since a typical network consists of thousands of NEs, it is very expensive to set up persistent connections between the middle-tier, the application server, and all the NEs. On the other hand, an end-user can select any of the NEs using the GUI to get details of the NE. The NMS must be responsive to the user request and hence should