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Oracle之SQL优化专题01-查看SQL执行计划的方法

2018-04-01 22:05  AlfredZhao  阅读(...)  评论(...编辑  收藏

在我2014年总结的“SQL Tuning 基础概述”中,其实已经介绍了一些查看SQL执行计划的方法,但是不够系统和全面,所以本次SQL优化专题,就首先要系统的介绍一下查看SQL执行计划的方法。
本文示例SQL为:

--set lines 1000 pages 1000
select a.empno, a.ename, b.dname, a.job, a.sal from emp a, dept b where a.deptno = b.deptno and empno = 7788;

1.explain plan for SQL;

通过explain plan for命令查看SQL的执行计划,这种方法SQL并不真实执行,一般适用于上线前的SQL预审,尤其对DML语句,由于SQL不执行,不用担心对生产数据造成影响。这种方法查看的执行计划有Predicate Information,无Statistics,查看到的执行计划不一定真实,第三方工具PL/SQL Developer中F5查看执行计划也是调用的这个方法。 使用explain plan for命令查看SQL的执行计划:
explain plan for 
select a.empno, a.ename, b.dname, a.job, a.sal from emp a, dept b where a.deptno = b.deptno and empno = 7788;

select * from table(dbms_xplan.display);

示例如下:

JINGYU@jyzhao1 >explain plan for 
  2  select a.empno, a.ename, b.dname, a.job, a.sal from emp a, dept b where a.deptno = b.deptno and empno = 7788;

Explained.

Elapsed: 00:00:00.01
JINGYU@jyzhao1 >select * from table(dbms_xplan.display);

PLAN_TABLE_OUTPUT
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Plan hash value: 1123238657

---------------------------------------------------------------------------
| Id  | Operation          | Name | Rows  | Bytes | Cost (%CPU)| Time     |
---------------------------------------------------------------------------
|   0 | SELECT STATEMENT   |      |     1 |    74 |     6   (0)| 00:00:01 |
|*  1 |  HASH JOIN         |      |     1 |    74 |     6   (0)| 00:00:01 |
|*  2 |   TABLE ACCESS FULL| EMP  |     1 |    52 |     3   (0)| 00:00:01 |
|   3 |   TABLE ACCESS FULL| DEPT |     4 |    88 |     3   (0)| 00:00:01 |
---------------------------------------------------------------------------

Predicate Information (identified by operation id):
---------------------------------------------------

   1 - access("A"."DEPTNO"="B"."DEPTNO")
   2 - filter("EMPNO"=7788)

Note
-----
   - dynamic sampling used for this statement (level=2)

20 rows selected.

Elapsed: 00:00:00.03
JINGYU@jyzhao1 >

2.set autotrace

通过set autotrace查看SQL的执行计划,这种方法SQL真实执行(除set autot trace exp针对select语句也不执行,但对DML语句还是会执行的),这种方法查看的执行计划有Predicate Information,有Statistics,查看的执行计划是准确的(注意:如果SQL中包含有绑定变量,那么用该方法所获取到的执行计划,也有可能不是真实的)。但由于SQL需要真实执行,所以对于有绑定变量值的SQL,还需要输入对应的变量值才可以执行,比较麻烦。 使用set autotrace查看SQL的执行计划:
set autotrace on
select a.empno, a.ename, b.dname, a.job, a.sal from emp a, dept b where a.deptno = b.deptno and empno = 7788;
set autotrace off

示例如下:

JINGYU@jyzhao1 >set autotrace on
JINGYU@jyzhao1 >select a.empno, a.ename, b.dname, a.job, a.sal from emp a, dept b where a.deptno = b.deptno and empno = 7788;

     EMPNO ENAME      DNAME          JOB              SAL
---------- ---------- -------------- --------- ----------
      7788 SCOTT      RESEARCH       ANALYST         3000

Elapsed: 00:00:00.01

Execution Plan
----------------------------------------------------------
Plan hash value: 1123238657

---------------------------------------------------------------------------
| Id  | Operation          | Name | Rows  | Bytes | Cost (%CPU)| Time     |
---------------------------------------------------------------------------
|   0 | SELECT STATEMENT   |      |     1 |    74 |     6   (0)| 00:00:01 |
|*  1 |  HASH JOIN         |      |     1 |    74 |     6   (0)| 00:00:01 |
|*  2 |   TABLE ACCESS FULL| EMP  |     1 |    52 |     3   (0)| 00:00:01 |
|   3 |   TABLE ACCESS FULL| DEPT |     4 |    88 |     3   (0)| 00:00:01 |
---------------------------------------------------------------------------

Predicate Information (identified by operation id):
---------------------------------------------------

   1 - access("A"."DEPTNO"="B"."DEPTNO")
   2 - filter("EMPNO"=7788)

Note
-----
   - dynamic sampling used for this statement (level=2)


Statistics
----------------------------------------------------------
          7  recursive calls
          0  db block gets
         15  consistent gets
          0  physical reads
          0  redo size
        814  bytes sent via SQL*Net to client
        520  bytes received via SQL*Net from client
          2  SQL*Net roundtrips to/from client
          0  sorts (memory)
          0  sorts (disk)
          1  rows processed

JINGYU@jyzhao1 >set autotrace off
JINGYU@jyzhao1 >

3.dbms_xplan

dbms_xplan下面有很多函数可以调用,其中最常用的是display_cursor和display_awr函数,下面依次介绍。

3.1 dbms_xplan.display_cursor(null,null,'allstats last')

通过dbms_xplan.display_cursor(null,null,'allstats last')查看SQL的执行计划,SQL会真实执行(对应的缺点不再赘述),这种方法查看的执行计划有Predicate Information,无Statistics,查看的执行计划是准确的,并且有每一步真实处理行数和时间。 使用dbms_xplan.display_cursor(null,null,'allstats last')查看SQL的执行计划:
--需要确认statistics_level设置为ALL,否则SQL语句第一个关键字后就需要加上/*+ gather_plan_statistics */,我习惯用前者
show parameter statistics_level(一般数据库默认是TYPICAL)
alter session set statistics_level = ALL;
select a.empno, a.ename, b.dname, a.job, a.sal from emp a, dept b where a.deptno = b.deptno and empno = 7788;
select * from table(dbms_xplan.display_cursor(null,null,'allstats last'));

示例如下:

JINGYU@jyzhao1 >alter session set statistics_level = ALL;

Session altered.

JINGYU@jyzhao1 >select a.empno, a.ename, b.dname, a.job, a.sal from emp a, dept b where a.deptno = b.deptno and empno = 7788;

     EMPNO ENAME      DNAME          JOB              SAL
---------- ---------- -------------- --------- ----------
      7788 SCOTT      RESEARCH       ANALYST         3000

JINGYU@jyzhao1 >select * from table(dbms_xplan.display_cursor(null,null,'allstats last'));

PLAN_TABLE_OUTPUT
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
SQL_ID  39dv3d8jkzyuw, child number 1
-------------------------------------
select a.empno, a.ename, b.dname, a.job, a.sal from emp a, dept b where
a.deptno = b.deptno and empno = 7788

Plan hash value: 1123238657

----------------------------------------------------------------------------------------------------------------
| Id  | Operation          | Name | Starts | E-Rows | A-Rows |   A-Time   | Buffers |  OMem |  1Mem | Used-Mem |
----------------------------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT   |      |      1 |        |      1 |00:00:00.01 |       7 |       |       |          |
|*  1 |  HASH JOIN         |      |      1 |      1 |      1 |00:00:00.01 |       7 |  1214K|  1214K|  762K (0)|
|*  2 |   TABLE ACCESS FULL| EMP  |      1 |      1 |      1 |00:00:00.01 |       3 |       |       |          |
|   3 |   TABLE ACCESS FULL| DEPT |      1 |      4 |      4 |00:00:00.01 |       4 |       |       |          |
----------------------------------------------------------------------------------------------------------------

Predicate Information (identified by operation id):
---------------------------------------------------

   1 - access("A"."DEPTNO"="B"."DEPTNO")
   2 - filter("EMPNO"=7788)

Note
-----
   - dynamic sampling used for this statement (level=2)


26 rows selected.

JINGYU@jyzhao1 >

3.2 dbms_xplan.display_cursor('&sql_id',null,'advanced')

通过dbms_xplan.display_cursor('&sql_id',null,'advanced')查看SQL的执行计划,这种方法查看的执行计划有Predicate Information,无Statistics,SQL是数据库中之前真实执行过的,对应执行计划是之前SQL真实执行过的执行计划,是准确的。使用这种方法的前提是需要SQL的cursor没有被刷出shared pool,否则查不到结果。 使用dbms_xplan.display_cursor('&sql_id',null,'advanced')查看SQL的执行计划:
--查询sql_id
select sql_id, sql_text from v$sql where sql_text like 'select a.empno%';
39dv3d8jkzyuw
--根据查询的sql_id查看执行计划
select * from table(dbms_xplan.display_cursor('&sql_id',null,'advanced'));
--附:函数DISPLAY_CURSOR的参数说明
FUNCTION DISPLAY_CURSOR RETURNS DBMS_XPLAN_TYPE_TABLE
 Argument Name                  Type                    In/Out Default?
 ------------------------------ ----------------------- ------ --------
 SQL_ID                         VARCHAR2                IN     DEFAULT
 CURSOR_CHILD_NO                NUMBER(38)              IN     DEFAULT
 FORMAT                         VARCHAR2                IN     DEFAULT

示例如下:

JINGYU@jyzhao1 >select * from table(dbms_xplan.display_cursor('&sql_id',null,'advanced'));
Enter value for sql_id: 39dv3d8jkzyuw
old   1: select * from table(dbms_xplan.display_cursor('&sql_id',null,'advanced'))
new   1: select * from table(dbms_xplan.display_cursor('39dv3d8jkzyuw',null,'advanced'))

PLAN_TABLE_OUTPUT
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
SQL_ID  39dv3d8jkzyuw, child number 0
-------------------------------------
select a.empno, a.ename, b.dname, a.job, a.sal from emp a, dept b where
a.deptno = b.deptno and empno = 7788

Plan hash value: 1123238657

---------------------------------------------------------------------------
| Id  | Operation          | Name | Rows  | Bytes | Cost (%CPU)| Time     |
---------------------------------------------------------------------------
|   0 | SELECT STATEMENT   |      |       |       |     6 (100)|          |
|*  1 |  HASH JOIN         |      |     1 |    74 |     6   (0)| 00:00:01 |
|*  2 |   TABLE ACCESS FULL| EMP  |     1 |    52 |     3   (0)| 00:00:01 |
|   3 |   TABLE ACCESS FULL| DEPT |     4 |    88 |     3   (0)| 00:00:01 |
---------------------------------------------------------------------------

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

   1 - SEL$1
   2 - SEL$1 / A@SEL$1
   3 - SEL$1 / B@SEL$1

Outline Data
-------------

  /*+
      BEGIN_OUTLINE_DATA
      IGNORE_OPTIM_EMBEDDED_HINTS
      OPTIMIZER_FEATURES_ENABLE('11.2.0.4')
      DB_VERSION('11.2.0.4')
      ALL_ROWS
      OUTLINE_LEAF(@"SEL$1")
      FULL(@"SEL$1" "A"@"SEL$1")
      FULL(@"SEL$1" "B"@"SEL$1")
      LEADING(@"SEL$1" "A"@"SEL$1" "B"@"SEL$1")
      USE_HASH(@"SEL$1" "B"@"SEL$1")
      END_OUTLINE_DATA
  */

Predicate Information (identified by operation id):
---------------------------------------------------

   1 - access("A"."DEPTNO"="B"."DEPTNO")
   2 - filter("EMPNO"=7788)

Column Projection Information (identified by operation id):
-----------------------------------------------------------

   1 - (#keys=1) "EMPNO"[NUMBER,22], "A"."ENAME"[VARCHAR2,10],
       "A"."JOB"[VARCHAR2,9], "A"."SAL"[NUMBER,22], "B"."DNAME"[VARCHAR2,14]
   2 - "EMPNO"[NUMBER,22], "A"."ENAME"[VARCHAR2,10],
       "A"."JOB"[VARCHAR2,9], "A"."SAL"[NUMBER,22], "A"."DEPTNO"[NUMBER,22]
   3 - "B"."DEPTNO"[NUMBER,22], "B"."DNAME"[VARCHAR2,14]

Note
-----
   - dynamic sampling used for this statement (level=2)

SQL_ID  39dv3d8jkzyuw, child number 1
-------------------------------------
select a.empno, a.ename, b.dname, a.job, a.sal from emp a, dept b where
a.deptno = b.deptno and empno = 7788

Plan hash value: 1123238657

---------------------------------------------------------------------------
| Id  | Operation          | Name | Rows  | Bytes | Cost (%CPU)| Time     |
---------------------------------------------------------------------------
|   0 | SELECT STATEMENT   |      |       |       |     6 (100)|          |
|*  1 |  HASH JOIN         |      |     1 |    74 |     6   (0)| 00:00:01 |
|*  2 |   TABLE ACCESS FULL| EMP  |     1 |    52 |     3   (0)| 00:00:01 |
|   3 |   TABLE ACCESS FULL| DEPT |     4 |    88 |     3   (0)| 00:00:01 |
---------------------------------------------------------------------------

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

   1 - SEL$1
   2 - SEL$1 / A@SEL$1
   3 - SEL$1 / B@SEL$1

Outline Data
-------------

  /*+
      BEGIN_OUTLINE_DATA
      IGNORE_OPTIM_EMBEDDED_HINTS
      OPTIMIZER_FEATURES_ENABLE('11.2.0.4')
      DB_VERSION('11.2.0.4')
      ALL_ROWS
      OUTLINE_LEAF(@"SEL$1")
      FULL(@"SEL$1" "A"@"SEL$1")
      FULL(@"SEL$1" "B"@"SEL$1")
      LEADING(@"SEL$1" "A"@"SEL$1" "B"@"SEL$1")
      USE_HASH(@"SEL$1" "B"@"SEL$1")
      END_OUTLINE_DATA
  */

Predicate Information (identified by operation id):
---------------------------------------------------

   1 - access("A"."DEPTNO"="B"."DEPTNO")
   2 - filter("EMPNO"=7788)

Column Projection Information (identified by operation id):
-----------------------------------------------------------

   1 - (#keys=1) "EMPNO"[NUMBER,22], "A"."ENAME"[VARCHAR2,10],
       "A"."JOB"[VARCHAR2,9], "A"."SAL"[NUMBER,22], "B"."DNAME"[VARCHAR2,14]
   2 - "EMPNO"[NUMBER,22], "A"."ENAME"[VARCHAR2,10],
       "A"."JOB"[VARCHAR2,9], "A"."SAL"[NUMBER,22], "A"."DEPTNO"[NUMBER,22]
   3 - "B"."DEPTNO"[NUMBER,22], "B"."DNAME"[VARCHAR2,14]

Note
-----
   - dynamic sampling used for this statement (level=2)

SQL_ID  39dv3d8jkzyuw, child number 2
-------------------------------------
select a.empno, a.ename, b.dname, a.job, a.sal from emp a, dept b where
a.deptno = b.deptno and empno = 7788

Plan hash value: 1123238657

---------------------------------------------------------------------------
| Id  | Operation          | Name | Rows  | Bytes | Cost (%CPU)| Time     |
---------------------------------------------------------------------------
|   0 | SELECT STATEMENT   |      |       |       |     6 (100)|          |
|*  1 |  HASH JOIN         |      |     1 |    74 |     6   (0)| 00:00:01 |
|*  2 |   TABLE ACCESS FULL| EMP  |     1 |    52 |     3   (0)| 00:00:01 |
|   3 |   TABLE ACCESS FULL| DEPT |     4 |    88 |     3   (0)| 00:00:01 |
---------------------------------------------------------------------------

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

   1 - SEL$1
   2 - SEL$1 / A@SEL$1
   3 - SEL$1 / B@SEL$1

Outline Data
-------------

  /*+
      BEGIN_OUTLINE_DATA
      IGNORE_OPTIM_EMBEDDED_HINTS
      OPTIMIZER_FEATURES_ENABLE('11.2.0.4')
      DB_VERSION('11.2.0.4')
      ALL_ROWS
      OUTLINE_LEAF(@"SEL$1")
      FULL(@"SEL$1" "A"@"SEL$1")
      FULL(@"SEL$1" "B"@"SEL$1")
      LEADING(@"SEL$1" "A"@"SEL$1" "B"@"SEL$1")
      USE_HASH(@"SEL$1" "B"@"SEL$1")
      END_OUTLINE_DATA
  */

Predicate Information (identified by operation id):
---------------------------------------------------

   1 - access("A"."DEPTNO"="B"."DEPTNO")
   2 - filter("EMPNO"=7788)

Column Projection Information (identified by operation id):
-----------------------------------------------------------

   1 - (#keys=1) "EMPNO"[NUMBER,22], "A"."ENAME"[VARCHAR2,10],
       "A"."JOB"[VARCHAR2,9], "A"."SAL"[NUMBER,22], "B"."DNAME"[VARCHAR2,14]
   2 - "EMPNO"[NUMBER,22], "A"."ENAME"[VARCHAR2,10],
       "A"."JOB"[VARCHAR2,9], "A"."SAL"[NUMBER,22], "A"."DEPTNO"[NUMBER,22]
   3 - "B"."DEPTNO"[NUMBER,22], "B"."DNAME"[VARCHAR2,14]

Note
-----
   - dynamic sampling used for this statement (level=2)


177 rows selected.

JINGYU@jyzhao1 >

由于上面没有指定CURSOR_CHILD_NO,所以全部都会显示出来,当然也可以指定某个CURSOR_CHILD_NO,比如说:

select * from table(dbms_xplan.display_cursor('&sql_id',0,'advanced'));

这样结果就只会显示CURSOR_CHILD_NO=0的执行计划。

3.3 dbms_xplan.display_awr('&sql_id')

通过dbms_xplan.display_awr('&sql_id')查看SQL的执行计划,这种方法查看的执行计划无Predicate Information,无Statistics,查看的执行计划是准确的。如果对应SQL没有被抓取到AWR中,就查不到结果。 使用dbms_xplan.display_awr('&sql_id')查看SQL的执行计划:
--查询sql_id
39dv3d8jkzyuw
--根据查询的sql_id查看执行计划
select * from table(dbms_xplan.display_awr('&sql_id'));
--附:函数DISPLAY_AWR的参数说明
FUNCTION DISPLAY_AWR RETURNS DBMS_XPLAN_TYPE_TABLE
 Argument Name                  Type                    In/Out Default?
 ------------------------------ ----------------------- ------ --------
 SQL_ID                         VARCHAR2                IN
 PLAN_HASH_VALUE                NUMBER(38)              IN     DEFAULT
 DB_ID                          NUMBER(38)              IN     DEFAULT
 FORMAT                         VARCHAR2                IN     DEFAULT

示例如下:

JINGYU@jyzhao1 >select * from table(dbms_xplan.display_awr('&sql_id'));
Enter value for sql_id: 39dv3d8jkzyuw

PLAN_TABLE_OUTPUT
------------------------------------------------------------------------------
SQL_ID 39dv3d8jkzyuw
--------------------
select a.empno, a.ename, b.dname, a.job, a.sal from emp a, dept b where
a.deptno = b.deptno and empno = 7788

Plan hash value: 1123238657

---------------------------------------------------------------------------
| Id  | Operation          | Name | Rows  | Bytes | Cost (%CPU)| Time     |
---------------------------------------------------------------------------
|   0 | SELECT STATEMENT   |      |       |       |     6 (100)|          |
|   1 |  HASH JOIN         |      |     1 |    74 |     6   (0)| 00:00:01 |
|   2 |   TABLE ACCESS FULL| EMP  |     1 |    52 |     3   (0)| 00:00:01 |
|   3 |   TABLE ACCESS FULL| DEPT |     4 |    88 |     3   (0)| 00:00:01 |
---------------------------------------------------------------------------

Note
-----
   - dynamic sampling used for this statement (level=2)


20 rows selected.

JINGYU@jyzhao1 >

也可以加参数显示更多的信息,比如可以显示出Outline Data,但没有Predicate Information,没有Statistics:

JINGYU@jyzhao1 >select * from table(dbms_xplan.display_awr('&sql_id',NULL,NULL,'advanced'));
Enter value for sql_id: 39dv3d8jkzyuw

PLAN_TABLE_OUTPUT
------------------------------------------------------------------------------
SQL_ID 39dv3d8jkzyuw
--------------------
select a.empno, a.ename, b.dname, a.job, a.sal from emp a, dept b where
a.deptno = b.deptno and empno = 7788

Plan hash value: 1123238657

---------------------------------------------------------------------------
| Id  | Operation          | Name | Rows  | Bytes | Cost (%CPU)| Time     |
---------------------------------------------------------------------------
|   0 | SELECT STATEMENT   |      |       |       |     6 (100)|          |
|   1 |  HASH JOIN         |      |     1 |    74 |     6   (0)| 00:00:01 |
|   2 |   TABLE ACCESS FULL| EMP  |     1 |    52 |     3   (0)| 00:00:01 |
|   3 |   TABLE ACCESS FULL| DEPT |     4 |    88 |     3   (0)| 00:00:01 |
---------------------------------------------------------------------------

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

   1 - SEL$1
   2 - SEL$1 / A@SEL$1
   3 - SEL$1 / B@SEL$1

Outline Data
-------------

  /*+
      BEGIN_OUTLINE_DATA
      IGNORE_OPTIM_EMBEDDED_HINTS
      OPTIMIZER_FEATURES_ENABLE('11.2.0.4')
      DB_VERSION('11.2.0.4')
      ALL_ROWS
      OUTLINE_LEAF(@"SEL$1")
      FULL(@"SEL$1" "A"@"SEL$1")
      FULL(@"SEL$1" "B"@"SEL$1")
      LEADING(@"SEL$1" "A"@"SEL$1" "B"@"SEL$1")
      USE_HASH(@"SEL$1" "B"@"SEL$1")
      END_OUTLINE_DATA
  */

Note
-----
   - dynamic sampling used for this statement (level=2)


44 rows selected.

JINGYU@jyzhao1 >

4.awrsqrpt

通过awrsqrpt查看SQL的执行计划,这种方式是导出SQL的awr报告,这种方法查看的执行计划无Predicate Information,但有Statistics,并且同时包含SQL单次和整体的统计信息,查看的执行计划是准确的。 使用awrsqrpt查看SQL的执行计划: @?/rdbms/admin/awrsqrpt
Specify the Begin and End Snapshot Ids
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Enter value for begin_snap: 240
Begin Snapshot Id specified: 240

Enter value for end_snap: 244
End   Snapshot Id specified: 244



Specify the SQL Id
~~~~~~~~~~~~~~~~~~
Enter value for sql_id: 39dv3d8jkzyuw
SQL ID specified:  39dv3d8jkzyuw
...
Report written to awrsqlrpt_1_240_244.html

这种执行计划的显示结果如下图:

5.10046 event

通过10046 event的跟踪文件查看SQL的执行计划,这种方法查看的执行计划是准确的,语句中函数,递归调用都会被详细列出,但没有谓词信息,而且这种方法获取执行计划比较麻烦。 使用10046 event查看SQL的执行计划:
alter session set events '10046 trace name context forever, level 12';
select a.empno, a.ename, b.dname, a.job, a.sal from emp a, dept b where a.deptno = b.deptno and empno = 7788;
alter session set events '10046 trace name context off';
--使用tkprof美化10046 event的跟踪文件,使其更易读:
tkprof jyzhao1_ora_14139.trc jyzhao1_ora_14139.txt sys=no

示例如下:

JINGYU@jyzhao1 >alter session set events '10046 trace name context forever, level 12';

Session altered.

JINGYU@jyzhao1 >select a.empno, a.ename, b.dname, a.job, a.sal from emp a, dept b where a.deptno = b.deptno and empno = 7788;

     EMPNO ENAME      DNAME          JOB              SAL
---------- ---------- -------------- --------- ----------
      7788 SCOTT      RESEARCH       ANALYST         3000

JINGYU@jyzhao1 >alter session set events '10046 trace name context off';

Session altered.

--使用tkprof美化10046 event的跟踪文件相关内容如下:

SQL ID: 39dv3d8jkzyuw Plan Hash: 1123238657

select a.empno, a.ename, b.dname, a.job, a.sal 
from
 emp a, dept b where a.deptno = b.deptno and empno = 7788


call     count       cpu    elapsed       disk      query    current        rows
------- ------  -------- ---------- ---------- ---------- ----------  ----------
Parse        1      0.01       0.02          0          8          0           0
Execute      1      0.00       0.00          0          0          0           0
Fetch        2      0.00       0.00          0          7          0           1
------- ------  -------- ---------- ---------- ---------- ----------  ----------
total        4      0.01       0.02          0         15          0           1

Misses in library cache during parse: 1
Optimizer mode: ALL_ROWS
Parsing user id: 91  
Number of plan statistics captured: 1

Rows (1st) Rows (avg) Rows (max)  Row Source Operation
---------- ---------- ----------  ---------------------------------------------------
         1          1          1  HASH JOIN  (cr=7 pr=0 pw=0 time=274 us cost=6 size=74 card=1)
         1          1          1   TABLE ACCESS FULL EMP (cr=3 pr=0 pw=0 time=67 us cost=3 size=52 card=1)
         4          4          4   TABLE ACCESS FULL DEPT (cr=4 pr=0 pw=0 time=15 us cost=3 size=88 card=4)


Elapsed times include waiting on following events:
  Event waited on                             Times   Max. Wait  Total Waited
  ----------------------------------------   Waited  ----------  ------------
  SQL*Net message to client                       2        0.00          0.00
  SQL*Net message from client                     2        6.55          6.56
********************************************************************************

关于阅读这个tkprof美化后文件的方法可以参考MOS文档:

  • TKProf Interpretation (9i and above) (文档 ID 760786.1)

reference

关于这个“Oracle之SQL优化专题”的系列,缘起是听了公司SQL优化专家团队的分享内容,自己想通过实际操作理解并逐渐测试完善,在我个人之前的职业生涯规划中一直都偏重于运维方向的DBA,对SQL优化方面了解的很少,兴趣也不高,是SQL优化专家团队的这次分享让我觉得SQL优化也是很有趣的,所以下决心从今天起单独开一个专题,自己也能逐渐系统的学习相关知识并记录下来。初步考虑该系列后续内容同时还会参考崔华的《基于Oracle的SQL优化》一书。最后感谢SQL优化专家团队的leader勇哥和其团队所有成员,是你们的这次分享让我有了做这个专题的动力。