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Chapter 1. Introduction > Choosing a replication strategy - Pg. 5

available for over 15 years and is well tested and reliable. Some of the most critical public service applications in the United States are built using IDS and rely on HDR to provide uninterrupted service. It has performed nearly flawlessly even in some of the worst natural and man-made disasters of the past several years. Thousands of other customers use it as part of their business continuity plan to protect against everything from component failure to power or network outages as well as natural or man-made events. ER, while it also replicates data, was designed and is implemented to share data objects throughout the entire database server environment. Unlike HDR, ER replicates transactions after they have completed rather than as a part of the commit/rollback. ER was designed and is implemented to provide two major benefits: 1. Improve client application performance through localized database server connections. 2. Improve availability of data for all applications. If the local server is unavailable, a replicated copy of the data can be accessed through a remote server. The benefits HDR and ER provide do not come without a cost. Both replication technologies require additional hardware resources including servers, disk storage, network infrastructure, and so on. Additional monitoring and alarming is