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DB2® Universal Database for OS/390® Version 7.1 Certification Guide by Susan Lawson, Richard Yevich

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Data Maintenance

The physical distribution of the data stored in tables has a significant effect on the performance of applications using those tables. The way the data is stored in a table is affected by the update, insert, and delete operations on the table. For example, a delete operation may leave empty pages of data that may not be reused later. Also, updates to variable-length columns may result in the new column value's not fitting in the same data page. This can cause the row to be moved to a different page and so produce internal gaps or unused space in the table. As a consequence, DB2 may have to read more physical pages to retrieve the information required by the application.

These scenarios are almost unavoidable. However, as the ...

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