메뉴 건너뛰기

Korea Oracle User Group

Guru's Articles

Explain the Explain Plan: Access Methods

명품관 2021.02.10 19:30 조회 수 : 293

원본 : https://sqlmaria.com/2021/01/12/explain-the-explain-plan-access-methods

 

 

Explain the Explain Plan: Access Methods

At the end of last year, I began a blog series on reading and interpreting Oracle execution plans. In this week’s post, I will tackle the aspect of execution plans that I get the most questions about, Access Methods.

What are Oracle Access Paths or Methods?

Access Methods or Access Paths are the techniques used by Oracle to access the data needed to answer a query. Access Methods can be divided into two categories; data accessed via a table scan or index access. You can find the individual Access Methods chosen by the Optimizer in the Operations column of an Execution table.

How Many Access Paths are available to the Optimizer?

Oracle supports nine different Access Methods today, as shown in the image below.

When will the Optimizer choose each of these methods, and what can I do to influence that decision?

To clearly explain how each of the Access Methods works and when it will be chosen, I’ve created a short video.

What if I don’t get the Access Method I want?

If the Access Method you see in an execution plan is not what you expect, check the cardinality estimates for that object are correct, and the join order allows the access method you desire. Remember, Optimizer transformations (the rewriting of your query to open up additional access methods) can also greatly impact the Access Method.

번호 제목 글쓴이 날짜 조회 수
공지 Guru's Article 게시판 용도 ecrossoug 2015.11.18 256
44 Explain the Explain Plan: Join Methods 명품관 2021.02.10 367
» Explain the Explain Plan: Access Methods 명품관 2021.02.10 293
42 Explain the Explain Plan: Cardinality Estimates 명품관 2021.02.09 274
41 Explaining the Explain Plan – How to Read and Interpret Execution Plans 명품관 2021.02.09 88
40 SQL Window Functions Cheat Sheet 명품관 2020.05.26 264
39 SQL Tuning Workshop 명품관 2020.02.20 2658
38 New initialization parameters, data dictionary views & dynamic performance views in Oracle Database 19c 명품관 2019.02.08 1592
37 More New Features in Oracle Database 19c 명품관 2019.02.08 1081
36 New Features of Performance Tuning in Oracle Database 19c 명품관 2019.02.08 682
35 New Features of RAC & ASM in Oracle 19c 명품관 2019.02.08 762
34 New Features of Data Guard in Oracle Database 19c 명품관 2019.02.08 592
33 New Features of Security in Oracle Database 19c 명품관 2019.02.08 3411
32 Patch conflicts 명품관 2019.02.07 737
31 New Features in Oracle Multitenant 19c 명품관 2019.02.07 645
30 New Features of Backup & Recovery in Oracle Database 19c 명품관 2019.02.07 238
29 New Features in Oracle Database 19c 명품관 2019.02.02 430
28 Different MOS Notes for xTTS PERL scripts – Use V4 scripts 명품관 2019.01.29 230
27 V$EVENT_NAME 뷰의 Name 컬럼에 정의된 event name에서 오는 오해 명품관 2017.03.08 238
26 Can I apply a BP on top of a PSU? Or vice versa? 명품관 2016.06.01 353
25 How to change the database name in 12c 명품관 2016.05.31 569
위로