sql執行計划：把SQL語句拆分為每個的操作步驟組合，按照一定的順序執行得出結果，查看並看懂執行計划是調優的關鍵步驟
查看執行計划的方法
- DBMS_XPLAN包
- sql*plus AUTO trace
- V$SQL_PLAN、DBA_HIST_SQL_PLAN
- ?/rdbms/admin/awrsqrpt.sql
- 工具類：toad、pl/SQL DEV
- 跟蹤dump：10046,10053
大多數人比較喜歡用工具直接看，以下來說明這些方式的不同用處
一、DBMS_XPLAN包
10g以后可以查看AWR中的語句執行計划，也可以查看當前內存中游標的執行計划。
主要有以下五個方法：
-
DISPLAY- 格式化並顯示plan table中內容，類似工具的F5（EXPLAIN PLAN FOR …） -
DISPLAY_AWR-格式和顯示存儲在AWR中的SQL語句的執行計划。數據來源: DBA_HIST_SQL_PLAN,DBA_HIST_SQLTEXT -
DISPLAY_CURSOR-格式和顯示任何加載游標執行計划的內容。數據來源：V$SQL_PLAN和V$SQL_PLAN_STATISTICS_ALL -
DISPLAY_SQL_PLAN_BASELINE- 顯示一個或多個執行計划的SQL語句通過SQL handle 標識 。數據來源：DBA_SQL_PLAN_BASELINES -
DISPLAY_SQLSET- 格式和顯示存儲在sql調優集中的執行計划內容。數據來源：ALL_SQLSET_STATEMENTS、ALL_SQLSET_PLANS
最常用的DISPLAY_AWR和DISPLAY_CURSOR，來闡述具體的調用方式，顯示的內容
（一）、DISPLAY_CURSOR
顯示當前shared pool->library cache中的執行計划
DBMS_XPLAN.DISPLAY_CURSOR( sql_id IN VARCHAR2 DEFAULT NULL, cursor_child_no IN NUMBER DEFAULT 0, format IN VARCHAR2 DEFAULT 'TYPICAL');
| 參數 | 說明（常用說明） |
| sql_id | SQL的唯一標識，取SELECT SQL_ID FROM V$SQL，為null的情況下，取上一條語句的執行計划 |
| cursor_child_no | 子游標的id號，為null，取出全部子游標的執行計划 |
| format | 輸出格式化 默認TYPICAL ADVANCED +PEEKED_BINDS ALLSTATS |
例子查看
#默認格式輸出select * from table(dbms_xplan.display_cursor('bjqjt2dfvya84',null))
SQL_ID bjqjt2dfvya84, child number 0
-------------------------------------
select * from emp where empno=7521
Plan hash value: 2949544139
--------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
--------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | | | 1 (100)| |
| 1 | TABLE ACCESS BY INDEX ROWID| EMP | 1 | 38 | 1 (0)| 00:00:01 |
|* 2 | INDEX UNIQUE SCAN | PK_EMP | 1 | | 0 (0)| |
--------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
2 - access("EMPNO"=7521)
＃格式化為ADVANCED +PEEKED_BINDS
select * from table(dbms_xplan.display_cursor('bjqjt2dfvya84',null,'ADVANCED +PEEKED_BINDS'))
SQL_ID bjqjt2dfvya84, child number 0
-------------------------------------
select * from emp where empno=7521
Plan hash value: 2949544139
--------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
--------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | | | 1 (100)| |
| 1 | TABLE ACCESS BY INDEX ROWID| EMP | 1 | 38 | 1 (0)| 00:00:01 |
|* 2 | INDEX UNIQUE SCAN | PK_EMP | 1 | | 0 (0)| |
--------------------------------------------------------------------------------------
Query Block Name / Object Alias (identified by operation id):
-------------------------------------------------------------
1 - SEL$1 / EMP@SEL$1
2 - SEL$1 / EMP@SEL$1
Outline Data
-------------
/*+
BEGIN_OUTLINE_DATA
IGNORE_OPTIM_EMBEDDED_HINTS
OPTIMIZER_FEATURES_ENABLE('11.2.0.3')
DB_VERSION('11.2.0.3')
OPT_PARAM('optimizer_dynamic_sampling' 0)
ALL_ROWS
OUTLINE_LEAF(@"SEL$1")
INDEX_RS_ASC(@"SEL$1" "EMP"@"SEL$1" ("EMP"."EMPNO"))
END_OUTLINE_DATA
*/
Predicate Information (identified by operation id):
---------------------------------------------------
2 - access("EMPNO"=7521)
Column Projection Information (identified by operation id):
-----------------------------------------------------------
1 - "EMPNO"[NUMBER,22], "EMP"."ENAME"[VARCHAR2,10],
"EMP"."JOB"[VARCHAR2,9], "EMP"."MGR"[NUMBER,22], "EMP"."HIREDATE"[DATE,7],
"EMP"."SAL"[NUMBER,22], "EMP"."COMM"[NUMBER,22], "EMP"."DEPTNO"[NUMBER,22]
2 - "EMP".ROWID[ROWID,10], "EMPNO"[NUMBER,22]
＃格式化ALLSTATS
兩種處理方式： * hint 'gather_plan_statistics' is used for the statement or
* parameter 'statistics_level' is set to 'ALL', at session or system level
select /*+gather_plan_statistics*/ * from emp where empno=7521
select * from table(dbms_xplan.display_cursor('dvj95t2z1gh2a',null,'ALLSTATS'))
SQL_ID dvj95t2z1gh2a, child number 0
-------------------------------------
select /*+gather_plan_statistics*/ * from emp where empno=7521
Plan hash value: 2949544139
------------------------------------------------------------------------------------------------
| Id | Operation | Name | Starts | E-Rows | A-Rows | A-Time | Buffers |
------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | | 1 |00:00:00.01 | 2 |
| 1 | TABLE ACCESS BY INDEX ROWID| EMP | 1 | 1 | 1 |00:00:00.01 | 2 |
|* 2 | INDEX UNIQUE SCAN | PK_EMP | 1 | 1 | 1 |00:00:00.01 | 1 |
------------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
2 - access("EMPNO"=7521)
A-ROW是實際的行數，E-ROW是優化器評估的
（二）、DISPLAY_AWR
顯示AWR中的SQL的執行計划，對分析歷史SQL慢的相當有幫組
DBMS_XPLAN.DISPLAY_AWR( sql_id IN VARCHAR2, plan_hash_value IN NUMBER DEFAULT NULL, db_id IN NUMBER DEFAULT NULL, format IN VARCHAR2 DEFAULT TYPICAL);
| 參數 | 常用說明 |
| SQL_ID | SQL的唯一標識，取SELECT SQL_ID FROM DBA_HIST_SQLTEXT |
| PLAN_HASH_VALUE | 指定SQL語句的PLAN_HASH_VALUE,忽略取全部的SQL_ID下的執行計划 |
| DB_ID | 默認取V$DATABASE.DATABASE_ID |
| FORMAT | 輸出格式化 默認TYPICAL ADVANCED +PEEKED_BINDS |
例子查看
#默認輸出的格式
select * from table(dbms_xplan.display_awr('bjqjt2dfvya84'));
SQL_ID bjqjt2dfvya84
--------------------
select * from emp where empno=7521
Plan hash value: 2949544139
--------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
--------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | | | 1 (100)| |
| 1 | TABLE ACCESS BY INDEX ROWID| EMP | 1 | 38 | 1 (0)| 00:00:01 |
| 2 | INDEX UNIQUE SCAN | PK_EMP | 1 | | 0 (0)| |
--------------------------------------------------------------------------------------
#通過格式化ADVANCED +PEEKED_BINDS
select * from table(dbms_xplan.display_awr('bjqjt2dfvya84',FORMAT=>'ADVANCED +PEEKED_BINDS'));
SQL_ID bjqjt2dfvya84
--------------------
select * from emp where empno=7521
Plan hash value: 2949544139
--------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
--------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | | | 1 (100)| |
| 1 | TABLE ACCESS BY INDEX ROWID| EMP | 1 | 38 | 1 (0)| 00:00:01 |
| 2 | INDEX UNIQUE SCAN | PK_EMP | 1 | | 0 (0)| |
--------------------------------------------------------------------------------------
Query Block Name / Object Alias (identified by operation id):
-------------------------------------------------------------
1 - SEL$1 / EMP@SEL$1
2 - SEL$1 / EMP@SEL$1
Outline Data
-------------
/*+
BEGIN_OUTLINE_DATA
IGNORE_OPTIM_EMBEDDED_HINTS
OPTIMIZER_FEATURES_ENABLE('11.2.0.3')
DB_VERSION('11.2.0.3')
OPT_PARAM('optimizer_dynamic_sampling' 0)
ALL_ROWS
OUTLINE_LEAF(@"SEL$1")
INDEX_RS_ASC(@"SEL$1" "EMP"@"SEL$1" ("EMP"."EMPNO"))
END_OUTLINE_DATA
*/
二、sqlplus autotrace
scott@GULL> set autotrace
用法: SET AUTOT[RACE] {OFF | ON | TRACE[ONLY]} [EXP[LAIN]] [STAT[ISTICS]]
可以體現執行語句的執行計划和統計信息
scott@GULL> SET autotrace trace
scott@GULL> select * from emp where empno=7521;
執行計划
----------------------------------------------------------
Plan hash value: 2949544139
--------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
--------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 38 | 1 (0)| 00:00:01 |
| 1 | TABLE ACCESS BY INDEX ROWID| EMP | 1 | 38 | 1 (0)| 00:00:01 |
|* 2 | INDEX UNIQUE SCAN | PK_EMP | 1 | | 0 (0)| 00:00:01 |
--------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
2 - access("EMPNO"=7521)
統計信息
----------------------------------------------------------
0 recursive calls
0 db block gets
2 consistent gets
0 physical reads
0 redo size
902 bytes sent via SQL*Net to client
508 bytes received via SQL*Net from client
1 SQL*Net roundtrips to/from client
0 sorts (memory)
0 sorts (disk)
1 rows processed
scott@GULL>
三、V$SQL_PLAN
直接取數據字典的源數據
scott@GULL> col id format 99; scott@GULL> col parent_id format 99999; scott@GULL> col operation format a25; scott@GULL> col options format a20; scott@GULL> select id,parent_id,operation,options from V$SQL_PLAN where sql_id='bjqjt2dfvya84'; ID PARENT_ID OPERATION OPTIONS --- --------- ------------------------- -------------------- 0 SELECT STATEMENT 1 0 TABLE ACCESS BY INDEX ROWID 2 1 INDEX UNIQUE SCAN
四、?/rdbms/admin/awrsqrpt.sql
查看AWR中執行計划，調用這個腳本后，相關的直觀展現
scott@GULL> @?/rdbms/admin/awrsqrpt.sql
Current Instance
~~~~~~~~~~~~~~~~
DB Id DB Name Inst Num Instance
----------- ------------ -------- ------------
3239200222 GULL 1 gullstby
Specify the Report Type
~~~~~~~~~~~~~~~~~~~~~~~
Would you like an HTML report, or a plain text report?
Enter 'html' for an HTML report, or 'text' for plain text
Defaults to 'html'
輸入 report_type 的值: html
Type Specified: html
Instances in this Workload Repository schema
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
DB Id Inst Num DB Name Instance Host
------------ -------- ------------ ------------ ------------
* 3239200222 1 GULL gullstby gull02
Using 3239200222 for database Id
Using 1 for instance number
Specify the number of days of snapshots to choose from
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Entering the number of days (n) will result in the most recent
(n) days of snapshots being listed. Pressing <return> without
specifying a number lists all completed snapshots.
輸入 num_days 的值: 1
Listing the last day's Completed Snapshots
Snap
Instance DB Name Snap Id Snap Started Level
------------ ------------ --------- ------------------ -----
gullstby GULL 368 01 6月 2016 10:08 1
369 01 6月 2016 10:12 1
Specify the Begin and End Snapshot Ids
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
輸入 begin_snap 的值: 368
Begin Snapshot Id specified: 368
輸入 end_snap 的值: 369
End Snapshot Id specified: 369
Specify the SQL Id
~~~~~~~~~~~~~~~~~~
輸入 sql_id 的值: bjqjt2dfvya84
SQL ID specified: bjqjt2dfvya84
Specify the Report Name
~~~~~~~~~~~~~~~~~~~~~~~
The default report file name is awrsqlrpt_1_368_369.html. To use this name,
press <return> to continue, otherwise enter an alternative.
輸入 report_name 的值: /home/oracle/0601.html
五、工具類：toad（ctrl+e）、pl/SQL DEV(f5)
工具類查看執行計划，非常快捷、簡單、能清楚知道每部步驟的優先級，但是他們實際調用的是EXPLAIN PLAN for，寫入plan_TABLE，是優化器的預評估，不是正在SQL執行時的執行計划。簡單分析是有用的，但是在你的應用程序中SQL很慢，常用的SQL用toad等很快，此時就不要在用工具快捷方式去查看執行計划，要去分析正在執行的執行計划，采用以上的內容方式。
toad(ctrl+e)
五、10046
10046這個事件是查看SQL具體的執行步驟，等待的是什么事件，實際內部調用的是哪些SQL。SQL語句執行很慢時，可以查看具體等待的是什么，導致執行這么慢。還有對我們了解create 、truncate具體在執行哪些語句有幫組。
SQL> conn /as sysdba
已連接。
SQL> ALTER SESSION SET EVENTS '10046 trace name context forever, level 28';
會話已更改。
SQL> select * from scott.emp where empno=7521;
SQL> select c.value || '/' || d.instance_name || '_ora_' ||
2 a.spid || '.trc' ||
3 case when e.value is not null then '_'||e.value end trace
4 from v$process a, v$session b, v$parameter c, v$instance d, v$parameter e
5 where a.addr = b.paddr
6 and b.sid = userenv('sid')
7 and c.name = 'user_dump_dest'
8 and e.name = 'tracefile_identifier';
TRACE
--------------------------------------------------------------------------------
/u01/app/oracle/diag/rdbms/orclstby/orcl/trace/orcl_ora_3288.trc 查看日志文件的內容
....
PARSING IN CURSOR #139774981787448 len=41 dep=0 uid=0 oct=3 lid=0 tim=1464851500943287 hv=3602254372 ad='d4180e00' sqlid='89mgdagbbc2j4'
select * from scott.emp where empno=7521
END OF STMT
PARSE #139774981787448:c=60990,e=224928,p=20,cr=444,cu=0,mis=1,r=0,dep=0,og=1,plh=2949544139,tim=1464851500943287
EXEC #139774981787448:c=0,e=0,p=0,cr=0,cu=0,mis=0,r=0,dep=0,og=1,plh=2949544139,tim=1464851500943287
WAIT #139774981787448: nam='SQL*Net message to client' ela= 1 driver id=1650815232 #bytes=1 p3=0 obj#=5473 tim=1464851500943295
WAIT #139774981787448: nam='Disk file operations I/O' ela= 29 FileOperation=2 fileno=4 filetype=2 obj#=75336 tim=1464851500943586
WAIT #139774981787448: nam='db file sequential read' ela= 11120 file#=4 block#=155 blocks=1 obj#=75336 tim=1464851500954730
WAIT #139774981787448: nam='db file sequential read' ela= 428 file#=4 block#=151 blocks=1 obj#=75335 tim=1464851500955277
FETCH #139774981787448:c=0,e=12010,p=2,cr=2,cu=0,mis=0,r=1,dep=0,og=1,plh=2949544139,tim=1464851500955332
STAT #139774981787448 id=1 cnt=1 pid=0 pos=1 obj=75335 op='TABLE ACCESS BY INDEX ROWID EMP (cr=2 pr=2 pw=0 time=11994 us cost=1 size=38 card=1)'
STAT #139774981787448 id=2 cnt=1 pid=1 pos=1 obj=75336 op='INDEX UNIQUE SCAN PK_EMP (cr=1 pr=1 pw=0 time=11487 us cost=0 size=0 card=1)'
WAIT #139774981787448: nam='SQL*Net message from client' ela= 297 driver id=1650815232 #bytes=1 p3=0 obj#=75335 tim=1464851500955736
FETCH #139774981787448:c=0,e=2,p=0,cr=0,cu=0,mis=0,r=0,dep=0,og=0,plh=2949544139,tim=1464851500955773
WAIT #139774981787448: nam='SQL*Net message to client' ela= 1 driver id=1650815232 #bytes=1 p3=0 obj#=75335 tim=1464851500955791
采用tkprof格式化10046，看起來更加的清晰
[oracle@gull2 ~]$ tkprof /u01/app/oracle/diag/rdbms/orclstby/orcl/trace/orcl_ora_3288.trc /home/oracle/3288.trc
查看3288.trc
SQL ID: 89mgdagbbc2j4 Plan Hash: 2949544139
select *afrom scott.emp where empno=7521
call count cpu elapsed disk query current rows
------- ------ -------- ---------- ---------- ---------- ---------- ----------
Parse 1 0.06 0.22 0 444 0 0
Execute 1 0.00 0.00 0 0 0 0
Fetch 2 0.00 0.01 2 2 0 1
------- ------ -------- ---------- ---------- ---------- ---------- ----------
total 4 0.06 0.23 2 446 0 1
Misses in library cache during parse: 1
Optimizer mode: ALL_ROWS
Parsing user id: SYS
Number of plan statistics captured: 1
Rows (1st) Rows (avg) Rows (max) Row Source Operation
---------- ---------- ---------- ---------------------------------------------------
1 1 1 TABLE ACCESS BY INDEX ROWID EMP (cr=2 pr=2 pw=0 time=11994 us cost=1 size=38 card=1)
1 1 1 INDEX UNIQUE SCAN PK_EMP (cr=1 pr=1 pw=0 time=11487 us cost=0 size=0 card=1)(object id 75336)
Elapsed times include waiting on following events:
Event waited on Times Max. Wait Total Waited
---------------------------------------- Waited ---------- ------------
SQL*Net break/reset to client 2 0.00 0.00
SQL*Net message to client 3 0.00 0.00
SQL*Net message from client 2 11.43 11.43
Disk file operations I/O 1 0.00 0.00
db file sequential read 2 0.01 0.01
六、10053
10053這個事件是查看為什么SQL語句評估出發的執行計划是這樣的，優化器如何評估出來這個執行計划的，記錄優化器的計算值
SQL> conn /as sysdba
已連接。
SQL> oradebug setmypid;
已處理的語句
SQL> oradebug event 10053 trace name context forever ,level 1;
已處理的語句
SQL> select * from scott.emp where empno=7521;
EMPNO ENAME JOB MGR
---------- ------------------------------ --------------------------- ----------
HIREDATE SAL COMM DEPTNO
-------------- ---------- ---------- ----------
7521 WARD SALESMAN 7698
22-2月 -81 1250 500 30
SQL> oradebug tracefile_name
/u01/app/oracle/diag/rdbms/orclstby/orcl/trace/orcl_ora_9109.trc
.......
Starting SQL statement dump
user_id=0 user_name=SYS module=sqlplus@gull2 (TNS V1-V3) action=
sql_id=b250dw0hyz0rs plan_hash_value=-1345423157 problem_type=3
----- Current SQL Statement for this session (sql_id=b250dw0hyz0rs) -----
select * from scott.emp where empno=7521
sql_text_length=49
sql= select * from scott.emp where empno=7521
----- Explain Plan Dump -----
----- Plan Table -----
============
Plan Table
============
-----------------------------------------------+-----------------------------------+
| Id | Operation | Name | Rows | Bytes | Cost | Time |
-----------------------------------------------+-----------------------------------+
| 0 | SELECT STATEMENT | | | | 1 | |
| 1 | TABLE ACCESS BY INDEX ROWID | EMP | 1 | 38 | 1 | 00:00:01 |
| 2 | INDEX UNIQUE SCAN | PK_EMP | 1 | | 0 | |
-----------------------------------------------+-----------------------------------+
Predicate Information:
----------------------
2 - access("EMPNO"=7521)
Content of other_xml column
===========================
db_version : 11.2.0.3
parse_schema : SYS
plan_hash : 2949544139
plan_hash_2 : 1767686164
Outline Data:
/*+
BEGIN_OUTLINE_DATA
IGNORE_OPTIM_EMBEDDED_HINTS
OPTIMIZER_FEATURES_ENABLE('11.2.0.3')
DB_VERSION('11.2.0.3')
ALL_ROWS
OUTLINE_LEAF(@"SEL$1")
INDEX_RS_ASC(@"SEL$1" "EMP"@"SEL$1" ("EMP"."EMPNO"))
END_OUTLINE_DATA
*/
總結
1、查看真實的執行計划，使用DBMS_XPLAN.DISPLAY_CUROR這個過程，可以清晰的展示SHARED_POOL-》libarary中的執行計划，不需要你重新去運行SQL語句，根據不同的格式輸出你需要的內容，可以查看出統計信息是否陳舊、謂詞中的字段類型是否有隱式轉化（導致索引不能使用）等
2、DBMS_XPLAN.DISPLAY_AWR，查看AWR中的執行計划，是否存在多個執行計划，代價比較高-》消耗性能厲害的，更加直觀的可以調用?/rdbms/admin/awrsqrpt.sql
3、sql*plus autotrace 需要重新去運行一遍SQL語句，查看現在運行的這個語句的執行計划，無法查看到，你程序中運行的那條語句的執行計划
4、工具調用（如toad 、PL/SQL DEV），實際采用的EXPLAIN PLAN FOR... 保存到plan_TABLE，是優化器的預評估。
5、10046的事件使用的范圍在調試一個語句執行很慢，想清楚具體等待的是什么，慢在哪個階段，還可以查看一些DDL的語句，內部語句的構造的方式，但查看執行計划，10046不是特別的方便，需要重新執行SQL語句，到服務器端拿日志文件
6、10053的事件可以用來分析 SQL語句為什么會做這個執行計划（如沒有走索引，而是走了全表掃描）