Managing Index Usage
Overview
To manage indexes effectively, it is
important to know
-
how SAS decides whether to use an index and which index to use
-
how to determine whether SAS is using an index
-
how to control whether SAS uses an index, or which index it uses.
Understanding How SAS Decides Whether to Use an Index
By default, each time
you submit a query (or other SAS program) that contains a WHERE expression,
SAS decides whether to use an index, or to read all the observations
in the data file sequentially. To make this decision, SAS does the
following:
-
Identifies an available index or indexes.
-
Estimates the number of rows that would be qualified. If multiple indexes are available, SAS selects the index that it ...
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