讀懂執行計劃

讀懂執行計劃
讀懂執行計劃
查看執行計劃的方法ios

  1. Explain Plan For SQL
    • 不實際執行SQL語句,生成的計劃未必是真實執行的計劃
    • 必需要有plan_table
    是一種手段但不是最好的
  2. SQLPLUS AUTOTRACE
    • 除set autotrace traceonly explain外均實際執行SQL,但仍未必
    是真實計劃
    • 必需要有plan_table
  3. SQL TRACE
    • 須要啓用10046戒者SQL_TRACE
    • 通常用tkprof看的更清楚些,固然10046裏自己也有執行計劃信息
  4. V$SQL和V$SQL_PLAN
    • 能夠查詢到多個子遊標的計劃信息了,可是看起來比較費勁
  5. Enterprise Manager
    • 能夠圖形化顯示執行計劃,但並不是全部環境有EM可用
  6. 其餘第三方工具
    • 注意 PL/SQL developer之類工具F5看到的執行計劃未必是真實的

D:\instantclient_12_2>sqlplus scott/tiger@clonepdb_plugsql

SQL*Plus: Release 12.2.0.1.0 Production on Fri Jan 12 13:54:31 2018數據庫

Copyright (c) 1982, 2016, Oracle. All rights reserved.session

Last Successful login time: Fri Jan 12 2018 11:18:59 +08:00分佈式

Connected to:
Oracle Database 12c Enterprise Edition Release 12.2.0.1.0 - 64bit Productionide

SCOTT@clonepdb_plug>set linesize 180
SCOTT@clonepdb_plug>set pagesize 0
SCOTT@clonepdb_plug>alter session set STATISTICS_LEVEL = ALL;工具

Session altered.優化

SCOTT@clonepdb_plug>select * from emp where ename='SMITH';
7369 SMITH CLERK 7902 1980-12-17 00:00:00 800 20this

SCOTT@clonepdb_plug>select * from table(dbms_xplan.display_cursor(null,null,'allstats'));
SQL_ID cgf95c3k5mszx, child number 0

select * from emp where ename='SMITH'線程

Plan hash value: 3956160932


| Id | Operation | Name | Starts | E-Rows | A-Rows | A-Time | Buffers |

| 0 | SELECT STATEMENT | | 1 | | 1 |00:00:00.01 | 8 |
|* 1 | TABLE ACCESS FULL| EMP | 1 | 1 | 1 |00:00:00.01 | 8 |

Predicate Information (identified by operation id):

1 - filter("ENAME"='SMITH')

18 rows selected.

SCOTT@clonepdb_plug>

須要受權
grant select on v$session to scott;
grant select on v
$sql to scott;
grant select on v_$sqlplan to scott;
grant select on v
$sql_plan_statistics_all to scott;

  1. 基本字段(老是可用的)

Id 執行計劃中每個操做(行)的標識符。若是數字前面帶有星號,意味着將在隨後提供這行包含的謂詞信息
Operation 對應執行的操做。也叫行源操做
Name 操做的對象名稱
2.查詢優化器評估信息

Rows(E-Rows) 預估操做返回的記錄條數
Bytes(E-Bytes) 預估操做返回的記錄字節數
TempSpc 預估操做使用臨時表空間的大小
Cost(%CPU) 預估操做所需的開銷。在括號中列出了CPU開銷的百分比。注意這些值是經過執行計劃計算出來的。換句話說,父操做的開銷包含子操做的開銷
Time 預估執行操做所須要的時間(HH:MM:SS)
3.分區(僅當訪問分區表時下列字段可見)

Pstart 訪問的第一個分區。若是解析時不知道是哪一個分區就設爲KEY,KEY(I),KEY(MC),KEY(OR),KEY(SQ)
Pstop 訪問的最後一個分區。若是解析時不知道是哪一個分區就設爲KEY,KEY(I),KEY(MC),KEY(OR),KEY(SQ)
4.並行和分佈式處理(僅當使用並行或分佈式操做時下列字段可見)

Inst 在分佈式操做中,指操做使用的數據庫連接的名字
TQ 在並行操做中,用於從屬線程間通訊的表隊列
IN-OUT 並行或分佈式操做間的關係
PQ Distrib 在並行操做中,生產者爲發送數據給消費者進行的分配
5.運行時統計(當設定參數statistics_level爲all或使用gather_plan_statistics提示時,下列字段可見)

Starts 指定操做執行的次數
A-Rows 操做返回的真實記錄數
A-Time 操做執行的真實時間(HH:MM:SS.FF)
6.I/O 統計(當設定參數statistics_level爲all或使用gather_plan_statistics提示時,下列字段可見)

Buffers 執行期間進行的邏輯讀操做數量
Reads 執行期間進行的物理讀操做數量
Writes 執行期間進行的物理寫操做數量
7.內存使用統計

OMem 最優執行所需內存的預估值
1Mem 一次經過(one-pass)執行所需內存的預估值
0/1/M 最優/一次經過/屢次經過(multipass)模式操做執行的次數
Used-Mem 最後一次執行時操做使用的內存量
Used-Tmp 最後一次執行時操做使用的臨時空間大小。這個字段必須擴大1024倍才能和其餘衡量內存的字段一致(好比,32k意味着32MB)
Max-Tmp 操做使用的最大臨時空間大小。這個字段必須擴大1024倍才能和其餘衡量內存的字段一致(好比,32k意味着32MB)

SCOTT@clonepdb_plug>explain plan for
2 select * from emp e,dept d
3 where e.deptno=d.deptno
4 and e.ename='SMITH';

Explained.

SCOTT@clonepdb_plug>select from table(dbms_xplan.display(null,null,'advanced'));
Plan hash value: 3625962092 -----是指執行計劃轉成的hash值,和執行效率無關,執行計劃的惟一標示
/
執行計劃部分*/

| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |

| 0 | SELECT STATEMENT | | 1 | 59 | 4 (0)| 00:00:01 |
| 1 | NESTED LOOPS | | 1 | 59 | 4 (0)| 00:00:01 |
| 2 | NESTED LOOPS | | 1 | 59 | 4 (0)| 00:00:01 |
| 3 | TABLE ACCESS FULL | EMP | 1 | 39 | 3 (0)| 00:00:01 |
|
4 | INDEX UNIQUE SCAN | PK_DEPT | 1 | | 0 (0)| 00:00:01 |
| 5 | TABLE ACCESS BY INDEX ROWID| DEPT | 1 | 20 | 1 (0)| 00:00:01 |

Query Block Name / Object Alias (identified by operation id): --這部分顯示的爲查詢塊名和對象別名

3 - SEL$1 / E@SEL$1 -E@SEL$1,對應到執行計劃中的操做ID爲3上,即在表E上的查詢,E爲別名,下面類同 SEL$爲select 的縮寫,位於塊1,相應的還有DEL$,INS$,UPD$等
4 - SEL$1 / D@SEL$1
5 - SEL$1 / D@SEL$1

Outline Data --提綱部分,這部分將執行計劃中的圖形化方式以文本形式來呈現,即轉換爲提示符方式

/+
BEGIN_OUTLINE_DATA
NLJ_BATCHING(@"SEL$1" "D"@"SEL$1") --指示優化器以嵌套循環關聯預提取的方式訪問表
USE_NL(@"SEL$1" "D"@"SEL$1") --使用USE_NL提示,即嵌套循環
LEADING(@"SEL$1" "E"@"SEL$1" "D"@"SEL$1") --指明前導表
INDEX(@"SEL$1" "D"@"SEL$1" ("DEPT"."DEPTNO"))-指明對於D上的訪問方式爲使用索引
FULL(@"SEL$1" "E"@"SEL$1") --指明對於E上的訪問方式爲全表掃描 br/>OUTLINE_LEAF(@"SEL$1")
ALL_ROWS
DB_VERSION('12.2.0.1')
OPTIMIZER_FEATURES_ENABLE('12.2.0.1')
IGNORE_OPTIM_EMBEDDED_HINTS
END_OUTLINE_DATA
/

Predicate Information (identified by operation id):--謂詞信息部分,在執行計劃中ID帶有星號的每一行均對應到下面中的一行

3 - filter("E"."ENAME"='SMITH')
4 - access("E"."DEPTNO"="D"."DEPTNO")

Column Projection Information (identified by operation id):--執行時每一步驟所返回的列,下面的不一樣步驟返回了不一樣的列

1 - (#keys=0) "E"."EMPNO"[NUMBER,22], "E"."ENAME"[VARCHAR2,10],
"E"."JOB"[VARCHAR2,9], "E"."MGR"[NUMBER,22], "E"."HIREDATE"[DATE,7],
"E"."SAL"[NUMBER,22], "E"."COMM"[NUMBER,22], "E"."DEPTNO"[NUMBER,22],
"D"."DEPTNO"[NUMBER,22], "D"."DNAME"[VARCHAR2,14], "D"."LOC"[VARCHAR2,13]
2 - (#keys=0) "E"."EMPNO"[NUMBER,22], "E"."ENAME"[VARCHAR2,10],
"E"."JOB"[VARCHAR2,9], "E"."MGR"[NUMBER,22], "E"."HIREDATE"[DATE,7],
"E"."SAL"[NUMBER,22], "E"."COMM"[NUMBER,22], "E"."DEPTNO"[NUMBER,22],
"D".ROWID[ROWID,10], "D"."DEPTNO"[NUMBER,22]
3 - "E"."EMPNO"[NUMBER,22], "E"."ENAME"[VARCHAR2,10], "E"."JOB"[VARCHAR2,9],
"E"."MGR"[NUMBER,22], "E"."HIREDATE"[DATE,7], "E"."SAL"[NUMBER,22],
"E"."COMM"[NUMBER,22], "E"."DEPTNO"[NUMBER,22]
4 - "D".ROWID[ROWID,10], "D"."DEPTNO"[NUMBER,22]
5 - "D"."DNAME"[VARCHAR2,14], "D"."LOC"[VARCHAR2,13]

Note--註釋與描述部分,下面的描述中給出了本次SQL語句使用了動態採樣功能

  • this is an adaptive plan

64 rows selected.

SCOTT@clonepdb_plug>select /+ gather_plan_statistics / * from emp e,dept d
2 where e.deptno=d.deptno
3 and e.ename='SMITH';
--注意此處增長了提示gather_plan_statistics而且該語句被執行 等同於alter session set STATISTICS_LEVEL = ALL;
7369 SMITH CLERK 7902 1980-12-17 00:00:00 800 20 20 RESEARCH
DALLAS

SCOTT@clonepdb_plug>select * from table(dbms_xplan.display_cursor(null,null,'iostats last'));--使用display_cursor獲取實際的執行計劃
SQL_ID 0wb0wwb3621n2, child number 0 --這部分給出了SQL語句的SQL_ID,子游標號以及原始的SQL語句

select /+ gather_plan_statistics / * from emp e,dept d
where e.deptno=d.deptno and e.ename='SMITH'

Plan hash value: 3625962092


| Id | Operation | Name | Starts | E-Rows | A-Rows | A-Time | Buffers |

| 0 | SELECT STATEMENT | | 1 | | 1 |00:00:00.01 | 9 |
| 1 | NESTED LOOPS | | 1 | 1 | 1 |00:00:00.01 | 9 |
| 2 | NESTED LOOPS | | 1 | 1 | 1 |00:00:00.01 | 8 |
| 3 | TABLE ACCESS FULL | EMP | 1 | 1 | 1 |00:00:00.01 | 7 |
|
4 | INDEX UNIQUE SCAN | PK_DEPT | 1 | 1 | 1 |00:00:00.01 | 1 |
| 5 | TABLE ACCESS BY INDEX ROWID| DEPT | 1 | 1 | 1 |00:00:00.01 | 1 |

Predicate Information (identified by operation id):

3 - filter("E"."ENAME"='SMITH')
4 - access("E"."DEPTNO"="D"."DEPTNO")

Note

  • this is an adaptive plan
    28 rows selected.

    SCOTT@clonepdb_plug>select * from table(dbms_xplan.display_cursor('6h1msdzb5hj7s',null,'ADVANCED peeked_binds ALLSTATS'));
    SQL_ID 6h1msdzb5hj7s, child number 0

    select /+ gather_plan_statistics / * from emp e,dept d
    where e.deptno=d.deptno and rownum<20 and ename like
    '%I%'

Plan hash value: 2662388210


| Id | Operation | Name | Starts | E-Rows |E-Bytes| Cost (%CPU)| E-Time | A-Rows | A-Time | Buffers | OMem | 1Mem | O/1/M |

| 0 | SELECT STATEMENT | | 1 | | | 4 (100)| | 4 |00:00:00.02 | 15 | | | |
| 1 | COUNT STOPKEY | | 1 | | | | | 4 |00:00:00.02 | 15 | | | |
|
2 | HASH JOIN | | 1 | 1 | 59 | 4 (0)| 00:00:01 | 4 |00:00:00.02 | 15 | 1055K| 1055K| 1/0/0|
|* 3 | TABLE ACCESS FULL| EMP | 1 | 1 | 39 | 3 (0)| 00:00:01 | 4 |00:00:00.01 | 7 | | | |
| 4 | TABLE ACCESS FULL| DEPT | 1 | 1 | 20 | 1 (0)| 00:00:01 | 3 |00:00:00.01 | 8 | | | |

Query Block Name / Object Alias (identified by operation id):

1 - SEL$1
3 - SEL$1 / E@SEL$1
4 - SEL$1 / D@SEL$1

Outline Data

/+
BEGIN_OUTLINE_DATA
FULL(@"SEL$1" "D"@"SEL$1")
USE_HASH(@"SEL$1" "D"@"SEL$1")br/>IGNORE_OPTIM_EMBEDDED_HINTS
OPTIMIZER_FEATURES_ENABLE('12.2.0.1')
DB_VERSION('12.2.0.1')
ALL_ROWS
OUTLINE_LEAF(@"SEL$1")
FULL(@"SEL$1" "E"@"SEL$1")
LEADING(@"SEL$1" "E"@"SEL$1" "D"@"SEL$1")
END_OUTLINE_DATA
/

Predicate Information (identified by operation id):

1 - filter(ROWNUM<20)
2 - access("E"."DEPTNO"="D"."DEPTNO")
3 - filter(("ENAME" LIKE '%I%' AND "ENAME" IS NOT NULL))

Column Projection Information (identified by operation id):

1 - "E"."DEPTNO"[NUMBER,22], "D"."DEPTNO"[NUMBER,22], "E"."EMPNO"[NUMBER,22], "ENAME"[VARCHAR2,10], "E"."JOB"[VARCHAR2,9],
"E"."MGR"[NUMBER,22], "E"."HIREDATE"[DATE,7], "E"."SAL"[NUMBER,22], "E"."COMM"[NUMBER,22], "D"."LOC"[VARCHAR2,13],
"D"."DEPTNO"[NUMBER,22], "D"."DNAME"[VARCHAR2,14], "D"."LOC"[VARCHAR2,13], "D"."DNAME"[VARCHAR2,14]
2 - (#keys=1) "E"."DEPTNO"[NUMBER,22], "D"."DEPTNO"[NUMBER,22], "E"."EMPNO"[NUMBER,22], "ENAME"[VARCHAR2,10], "E"."JOB"[VARCHAR2,9],
"E"."MGR"[NUMBER,22], "E"."HIREDATE"[DATE,7], "E"."SAL"[NUMBER,22], "E"."COMM"[NUMBER,22], "D"."LOC"[VARCHAR2,13],
"D"."DEPTNO"[NUMBER,22], "D"."DNAME"[VARCHAR2,14], "D"."LOC"[VARCHAR2,13], "D"."DNAME"[VARCHAR2,14]
3 - "E"."EMPNO"[NUMBER,22], "ENAME"[VARCHAR2,10], "E"."JOB"[VARCHAR2,9], "E"."MGR"[NUMBER,22], "E"."HIREDATE"[DATE,7],
"E"."SAL"[NUMBER,22], "E"."COMM"[NUMBER,22], "E"."DEPTNO"[NUMBER,22]
4 - "D"."DEPTNO"[NUMBER,22], "D"."DNAME"[VARCHAR2,14], "D"."LOC"[VARCHAR2,13]

Note

  • this is an adaptive plan

66 rows selected.

SCOTT@clonepdb_plug>

讀懂執行計劃
讀懂執行計劃
讀懂執行計劃
讀懂執行計劃

讀懂執行計劃
讀懂執行計劃

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