메뉴 건너뛰기

Korea Oracle User Group

Guru's Articles

원문 : https://sqlmaria.com/2020/10/27/explaining-the-explain-plan-how-to-read-and-interpret-execution-plans/

Explaining the Explain Plan – How to Read and Interpret Execution Plans

 

Examining the different aspects of an execution plan, from cardinality estimates to parallel execution, and understanding what information you should glean from it can be overwhelming even for the most experienced DBA.

That’s why I’ve put together a series of short videos that will walk you through each aspect of the plan and explain what information you can find there and what to do if the plan isn’t what you were expecting.

What is an Execution Plan?

The series starts at the very beginning with a comprehensive overview of what an execution plan is and what information is displayed in each section. After all, you can’t learn to interpret what is happening in a plan, until you know what a plan actually is.

How to Generate an Execution Plan?

Although multiple different tools will display an Oracle Execution Plan for you, there really are only two ways to generate the plan. You can use the Explain Plan command, or you can view the execution plan of a SQL statement currently in the Cursor Cache using the dictionary view V$SQL_Plan. This session covers both techniques for you and provides insights into what additional information you can get the Optimizer to share with you when you generate a plan. It also explains why you don’t always get the same plan with each approach, as I discussed in an earlier post.

How to use DBMS_XPLAN to FORMAT an Execution Plan

The FORMAT parameter within the DBMS_XPLAN.DISPLAY_CURSOR function is the best tool to show you detailed information about a what’s happened in an execution plan including the bind variable values used, the actual number of rows returned by each step, and how much time was spent on each step.  I’ve also covered a lot of the content in this video in a previous post.

Part 2 of the series covers Cardinality Estimates and what you can do to improve them!

Part 3 of the series covers access Methods and what you can do if you don’t get the access method you were expecting.

Part 4 of the series covers Join Methods and when you can expect each one and what to do if you don’t get the join method you were expecting.

Remember you can always get more information on the Oracle Optimizer on the Optimizer team’s blog.

 

번호 제목 글쓴이 날짜 조회 수
공지 Guru's Article 게시판 용도 ecrossoug 2015.11.18 600
44 Explain the Explain Plan: Join Methods 명품관 2021.02.10 730
43 Explain the Explain Plan: Access Methods 명품관 2021.02.10 945
42 Explain the Explain Plan: Cardinality Estimates 명품관 2021.02.09 614
» Explaining the Explain Plan – How to Read and Interpret Execution Plans 명품관 2021.02.09 487
40 SQL Window Functions Cheat Sheet 명품관 2020.05.26 436
39 SQL Tuning Workshop 명품관 2020.02.20 8152
38 New initialization parameters, data dictionary views & dynamic performance views in Oracle Database 19c 명품관 2019.02.08 1910
37 More New Features in Oracle Database 19c 명품관 2019.02.08 6583
36 New Features of Performance Tuning in Oracle Database 19c 명품관 2019.02.08 914
35 New Features of RAC & ASM in Oracle 19c 명품관 2019.02.08 944
34 New Features of Data Guard in Oracle Database 19c 명품관 2019.02.08 2000
33 New Features of Security in Oracle Database 19c 명품관 2019.02.08 5045
32 Patch conflicts 명품관 2019.02.07 965
31 New Features in Oracle Multitenant 19c 명품관 2019.02.07 739
30 New Features of Backup & Recovery in Oracle Database 19c 명품관 2019.02.07 427
29 New Features in Oracle Database 19c 명품관 2019.02.02 538
28 Different MOS Notes for xTTS PERL scripts – Use V4 scripts 명품관 2019.01.29 417
27 V$EVENT_NAME 뷰의 Name 컬럼에 정의된 event name에서 오는 오해 명품관 2017.03.08 367
26 Can I apply a BP on top of a PSU? Or vice versa? 명품관 2016.06.01 396
25 How to change the database name in 12c 명품관 2016.05.31 1932
위로