bdfd1m0eDatabase Administration

Duplicating Data to Improve Performance

Because duplicating data can improve retrieval speeds, you may choose to reintroduce some data duplication in the tables you have been working on.

Note:
Data should be duplicated for performance reasons only. Data duplication can result in extra updating, which in turn requires more I/O processing. You must ensure that the extra I/O processing for updating does not outweigh the I/O processing saved through the duplication itself. Because I/O processing can represent a major part of the lifetime of a transaction lifetime, it is important to minimize I/O processing.

Data duplication can also lead to inconsistent data being held. However, some data fields are more suitable for duplication than others. There is less risk of data inconsistency if you duplicate fields whose values do not change often. For example, a passenger's name is unlikely to change whereas seat availability changes with every seat sold.

You must balance these factors against the potential improvement in retrieval speeds.

In the examples that follow, you can see how selected duplication of data can improve the performance of your database.