Best Practices for Gathering Optimizer Statistics with Oracle Database 12c (White Paper)

Oracle White Paper
Best Practices for Gathering Optimizer Statistics with Oracle Database 12c

Introduction

The Oracle Optimizer examines all of the possible plans for a SQL statement and picks the one with the lowest cost, where cost represents the estimated resource usage for a given plan. In order for the Optimizer to accurately determine the cost for an execution plan it must have information about all of the objects (table and indexes) accessed in the SQL statement as well as information about the system on which the SQL statement will be run.
This necessary information is commonly referred to as Optimizer statistics.
Understanding and managing Optimizer statistics is key to optimal SQL execution. Knowing when and how to gather statistics in a timely manner is critical to maintaining acceptable performance. This whitepaper is the second of a two part series on Optimizer statistics. The first part of this series, Understanding Optimizer Statistics, focuses on the concepts of statistics and will be referenced several times in this paper as a source of additional
information. 
This paper will discuss in detail, when and how to gather statistics for the most common scenarios seen in an Oracle Database. The topics are

• How to gather statistics
• When to gather statistics
• Improving the efficiency of gathering statistics
• When not to gather statistics
• Gathering other types of statistics

http://www.oracle.com/technetwork/database/bi-datawarehousing/twp-bp-for-stats-gather-12c-1967354.pdf