Oracle Database 19c 收集统计信息的最佳实践.pdf

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2019-06-20

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Best Practices for Gathering

Optimizer Statistics with Oracle

Database 19c

ORACLE WHITE PAPER / MARCH 13, 2019

2 WHITE PAPER / Best Practices for Gathering Optimizer Statistics with Oracle Database 19c

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 part one of this series, Understanding

Optimizer Statistics with Oracle Database 19c, 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 quality of statistics

 Gathering statistics more quickly

 When not to gather statistics

 Gathering other types of statistics

DISCLAIMER

This document in any form, software or printed matter, contains proprietary information that is the

exclusive property of Oracle. Your access to and use of this confidential material is subject to the

terms and conditions of your Oracle software license and service agreement, which has been

executed and with which you agree to comply. This document and information contained herein may

not be disclosed, copied, reproduced or distributed to anyone outside Oracle without prior written

consent of Oracle. This document is not part of your license agreement nor can it be incorporated

into any contractual agreement with Oracle or its subsidiaries or affiliates.

This document is for informational purposes only and is intended solely to assist you in planning for

the implementation and upgrade of the product features described. It is not a commitment to deliver

any material, code, or functionality, and should not be relied upon in making purchasing decisions.

The development, release, and timing of any features or functionality described in this document

remains at the sole discretion of Oracle.

Due to the nature of the product architecture, it may not be possible to safely include all features

described in this document without risking significant destabilization of the code.

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