Microsoft SQL Server 2014 Unleashed
by Ray Rankins, Paul Bertucci, Chris Gallelli, Alex T. Silverstein
Estimating Access Path Cost
After the selectivity of each of the SARGs, OR clauses, and join conditions is determined, the next phase of optimization is estimating the access path cost of each search or join expression. The Query Optimizer attempts to identify the total cost of various access paths to the data and determine which path results in the lowest cost to return the matching rows for an expression.
The primary cost of an access path, especially for single-table queries, is the number of logical I/Os required to retrieve the data. Using the available statistics and the information stored in SQL Server regarding the average number of rows per page and the number of pages in the table, the Query Optimizer estimates the number of logical ...
Become an O’Reilly member and get unlimited access to this title plus top books and audiobooks from O’Reilly and nearly 200 top publishers, thousands of courses curated by job role, 150+ live events each month,
and much more.
Read now
Unlock full access