执行计划

1. 预执行 explain plan for

实际并没有执行SQL语句。

SQL> explain plan for select ca_cstid from c_acc;

Explained.

SQL> @?/rdbms/admin/utlxpls

PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------------
Plan hash value: 3827578295

-----------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
-----------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 7 | 1 (0)| 00:00:01 |
| 1 | INDEX FULL SCAN | DEPT_ACC | 1 | 7 | 1 (0)| 00:00:01 |
-----------------------------------------------------------------------------

8 rows selected.

SQL> @?/rdbms/admin/utlxplp

PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------------
Plan hash value: 3827578295

-----------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
-----------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 7 | 1 (0)| 00:00:01 |
| 1 | INDEX FULL SCAN | DEPT_ACC | 1 | 7 | 1 (0)| 00:00:01 |
-----------------------------------------------------------------------------

8 rows selected.

SQL> select plan_table_output from table(DBMS_XPLAN.DISPLAY());

PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------------
Plan hash value: 3827578295

-----------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
-----------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 7 | 1 (0)| 00:00:01 |
| 1 | INDEX FULL SCAN | DEPT_ACC | 1 | 7 | 1 (0)| 00:00:01 |
-----------------------------------------------------------------------------

8 rows selected.

2. 即时执行计划

在执行SQL的同时查看执行计划。

SQL> set autotrace traceonly; # 运行查询但不显示查询结果；显示执行计划与统计信息
SQL> select ca_cstid from c_acc;

Execution Plan
----------------------------------------------------------
Plan hash value: 3827578295

-----------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
-----------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 7 | 1 (0)| 00:00:01 |
| 1 | INDEX FULL SCAN | DEPT_ACC | 1 | 7 | 1 (0)| 00:00:01 |
-----------------------------------------------------------------------------

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

SQL>

SQL> set autotrace traceonly explain #不运行查询（DML操作会运行）；显示执行计划，不显示统计信息。
SQL> select ca_cstid from c_acc;

Execution Plan
----------------------------------------------------------
Plan hash value: 3827578295

-----------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
-----------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 7 | 1 (0)| 00:00:01 |
| 1 | INDEX FULL SCAN | DEPT_ACC | 1 | 7 | 1 (0)| 00:00:01 |
-----------------------------------------------------------------------------

SQL>

3. 查看指定SQL执行计划

查看已经执行过的SQL的执行计划

查看v$sql_plan中最后一个会话SQL的执行计划

SQL> set linesize 160
SQL> select plan_table_output from table(dbms_xplan.display_cursor());

Execution Plan
----------------------------------------------------------
Plan hash value: 3713220770

----------------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
----------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 8168 | 16336 | 29 (0)| 00:00:01 |
| 1 | COLLECTION ITERATOR PICKLER FETCH| DISPLAY_CURSOR | 8168 | 16336 | 29 (0)| 00:00:01 |
----------------------------------------------------------------------------------------------------

通过SQL_ID查询其执行计划

SQL> set autotrace traceonly

SQL> select mb_id,mb_tname from mng_bak;

2294 rows selected.

Execution Plan
----------------------------------------------------------
Plan hash value: 1749878440

-----------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
-----------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 2294 | 59644 | 12 (0)| 00:00:01 |
| 1 | TABLE ACCESS FULL| MNG_BAK | 2294 | 59644 | 12 (0)| 00:00:01 |
-----------------------------------------------------------------------------

Statistics
----------------------------------------------------------
0 recursive calls
0 db block gets
188 consistent gets
0 physical reads
0 redo size
90151 bytes sent via SQL*Net to client
2191 bytes received via SQL*Net from client
154 SQL*Net roundtrips to/from client
0 sorts (memory)
0 sorts (disk)
2294 rows processed

SQL>

SQL> set autotrace off
SQL> select sql_id,child_number from v$sql where sql_text like 'select mb_id,mb_tname from mng_bak%';

SQL_ID CHILD_NUMBER
------------- ------------
bk8rtgsb6jm37 0

SQL>

SQL> set linesize 80
SQL> select plan_table_output from table(dbms_xplan.display_cursor('bk8rtgsb6jm37',0,'TYPICAL'));

PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------------
SQL_ID bk8rtgsb6jm37, child number 0
-------------------------------------
select mb_id,mb_tname from mng_bak

Plan hash value: 1749878440

-----------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
-----------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | | | 12 (100)| |
| 1 | TABLE ACCESS FULL| MNG_BAK | 2294 | 59644 | 12 (0)| 00:00:01 |

PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------------
-----------------------------------------------------------------------------

13 rows selected.

4. 历史执行计划 dba_hist_sql_plan

dba_hist_sql_plan 与 dba_hist_sqltext 通过SQL_ID关联。

SQL> desc dba_hist_sqltext
Name Null? Type
----------------------------------------- -------- ----------------------------
DBID NOT NULL NUMBER
SQL_ID NOT NULL VARCHAR2(13)
SQL_TEXT CLOB
COMMAND_TYPE NUMBER

SQL> select p.* from dba_hist_sqltext t,table(DBMS_XPLAN.DISPLAY_AWR(t.sql_id,null,null,'TYPICAL')) p where t.sql_text like 'select mb_id,mb_tname from mng_bak%';

no rows selected