Building the Data Warehouse

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monitor data warehouse use

Figure 4.4 The support software needed to make storage overflow possible.

the modern rendition is a robotically controlled silo of storage where the human hand never touches the storage unit.

The alternate forms of storage are cheap, reliable, and capable of storing huge amounts of data, much more so than is feasible for storage on high-performance disk devices—the alternate of storage. In doing so, the alternate forms of storage as overflow for the data warehouse allow. In some cases, a query facility that can operate independently of the storage device is desirable. In this case when a user makes a query there is no prior knowledge of where the data resides. The query is issued, and the system then finds the data regardless of where it is.

While it is convenient for the end user to merely “go get the data,” there is a performance implication. If the end user frequently accesses data that is in alternate storage, the query will not run quickly, and many machine resources will be consumed in the servicing of the request. Therefore, the data architect is best advised to make sure that the data that resides in alternate storage is accessed infrequently.

There are several ways to ensure infrequently accessed data resides in alternate storage. A simple way is to place data in alternate storage when it reaches a certain age—say, 24 months. Another way is to place certain types of data in

alternate storage and other types in disk storage. Monthly summary of customer records may be placed in disk storage, while details that support the monthly summary are placed in alternate storage.

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