Space costs of indexes

The first cost of an index is disk space. The presence of an index can add many pages to a dbspace; it is easy to have as many index pages as row pages in an indexed table. Additionally, in an environment where multiple languages are used, indexes created for each language require additional disk space.

When you consider space costs, also consider whether increasing the page size of a standard or temporary dbspace is beneficial in your environment. If you want a longer key length than is available for the default page size, you can increase the page size. If you increase the page size, the size must be an integral multiple of the default page size, not greater than 16K bytes.

You might not want to increase the page size if your application contains small sized rows. Increasing the page size for an application that randomly accesses small rows might decrease performance. In addition, a page lock on a larger page will lock more rows, reducing concurrency in some situations.

You can save disk space by compressing detached B-tree indexes, consolidating free space in the index, and returning the free space to the dbspace.

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