Indexing strategy

 

There are two approaches to index creation: proactive and reactive. As the name implies proactive index creation involves anticipating which columns will be most often used for selection, joining, grouping and ordering; and then building indexes over those columns. In the reactive approach, indexes are created based on optimizer feedback, query implementation plan, and system performance measurements.

It is useful to initially build indexes based on the database model and application(s) and not any particular query. As a starting point, consider designing basic indexes based on the following criteria:

• Primary and foreign key columns based on the database model

• Commonly used local selection columns, including columns that are dependent, such as an automobile's make and model

• Commonly used join columns not considered primary or foreign key columns

• Commonly used grouping columns

• Reactive approach to tuning
  To perform reactive tuning, build a prototype of the proposed application without any indexes and start running some queries or build an initial set of indexes and start running the application to see what gets used and what does not. Even with a smaller database, the slow running queries will become obvious very quickly.

• Proactive approach to tuning
  Typically you will create an index for the most selective columns and create statistics for the least selective columns in a query. By creating an index, the optimizer knows that the column is selective and it also gives the optimizer the ability to use that index to implement the query.

 

Parent topic:

Creating an index strategy

 

Related information

Indexing and statistics strategies for DB2 UDB for iSeries