Building the Data Warehouse

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Figure 5.4 Still more technological requirements for the data warehouse.

One of the effects of the lock manager is that it consumes a fair amount of resources, even when data is not being updated. Merely turning the lock manager on requires overhead. Therefore, to streamline the data warehouse environment, being able to selectively turn the lock manager off and on is necessary.

Index-Only Processing

A fairly standard database management system feature is the ability to do index-only processing. On many occasions, it is possible to service a request by simply looking in an index (or indexes)—without going to the primary source of data. This is, of course, much more efficient. Not all DBMSs, though, are intelligent enough to know that a request can be satisfied in the index.

Technology that is optimal for the data warehouse environment looks for data in the indexes exclusively if such a request can be formulated and/or allow the query user to specify that such an index query has been specified. The DBMS technology must offer the DSS end user the option of specifying that if an index query can be executed, the query be satisfied in that manner.

Fast Restore

A simple but important technological feature of the data warehouse environment is the ability to quickly restore a data warehouse table from non-DASD storage. When a restore can be done from secondary storage, enormous savings may be possible. Without the ability to restore data quickly from secondary storage, the standard practice is to double the amount of DASD and use one-half of the DASD as a recovery/restore repository.

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