Oracle之SQL优化专题01-查看SQL执行计划的方法
2018-04-01 22:05
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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:
1.explain plan for
2.set autotrace
3.dbms_xplan
3.1 dbms_xplan.display_cursor(null,null,'allstats last')
3.2 dbms_xplan.display_cursor('&sql_id',null,'advanced')
3.3 dbms_xplan.display_awr('&sql_id')
4.awrsqrpt
5.10046 event
reference
使用explain plan for命令查看SQL的执行计划:
示例如下:
使用set autotrace查看SQL的执行计划:
示例如下:
使用dbms_xplan.display_cursor(null,null,'allstats last')查看SQL的执行计划:
示例如下:
使用dbms_xplan.display_cursor('&sql_id',null,'advanced')查看SQL的执行计划:
示例如下:
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:
这样结果就只会显示CURSOR_CHILD_NO=0的执行计划。
使用dbms_xplan.display_awr('&sql_id')查看SQL的执行计划:
示例如下:
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:
使用awrsqrpt查看SQL的执行计划:
@?/rdbms/admin/awrsqrpt
这种执行计划的显示结果如下图:
使用10046 event查看SQL的执行计划:
示例如下:
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)
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
2.set autotrace
3.dbms_xplan
3.1 dbms_xplan.display_cursor(null,null,'allstats last')
3.2 dbms_xplan.display_cursor('&sql_id',null,'advanced')
3.3 dbms_xplan.display_awr('&sql_id')
4.awrsqrpt
5.10046 event
reference
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。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。相关文章推荐
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