如何使用dbms_xplan查看执行计划
小编给大家分享一下如何使用dbms_xplan查看执行计划，相信大部分人都还不怎么了解，因此分享这篇文章给大家参考一下，希望大家阅读完这篇文章后大有收获，下面让我们一起去了解一下吧！
概述
dbms_xplan包提供了多样的，预定义的方式去解释执行计划。sql执行计划，执行时间等信息都存储与v$sql_plan,v$sql_plan_statistics_all视图中。此包运行的权限是执行用户，不是包的拥有者sys。
当执行diplay_awr时，需要DBA_HIST_SQL_PLAN, DBA_HIST_SQLTEXT, and V$DATABASE的查询权限
当执行display_cursor时需要V$SQL_PLAN, V$SESSION and V$SQL_PLAN_STATISTICS_ALL的查询权限
当执行display_sql_plan_baseline时，需要DBA_SQL_PLAN_BASELINES的查询权限
当执行display_sqlset时，需要ALL_SQLSET_STATEMENTS and ALL_SQLSET_PLANS的查询权限
以上的所有权限都在SELECT_CATALOG角色中，所以直接赋权SELECT_CATALOG就可以了。
dbms_xplan中有许多功能，我这里着重研究其中几个常用的
SQL> desc dbms_xplan;
…
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
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
FUNCTION DISPLAY_PLAN RETURNS CLOB
Argument Name Type In/Out Default?
------------------------------ ----------------------- ------ --------
TABLE_NAME VARCHAR2 IN DEFAULT
STATEMENT_ID VARCHAR2 IN DEFAULT
FORMAT VARCHAR2 IN DEFAULT
FILTER_PREDS VARCHAR2 IN DEFAULT
TYPE VARCHAR2 IN DEFAULT
FUNCTION DISPLAY_SQLSET RETURNS DBMS_XPLAN_TYPE_TABLE
Argument Name Type In/Out Default?
------------------------------ ----------------------- ------ --------
SQLSET_NAME VARCHAR2 IN
SQL_ID VARCHAR2 IN
PLAN_HASH_VALUE NUMBER(38) IN DEFAULT
FORMAT VARCHAR2 IN DEFAULT
SQLSET_OWNER VARCHAR2 IN DEFAULT
FUNCTION DISPLAY_SQL_PLAN_BASELINE RETURNS DBMS_XPLAN_TYPE_TABLE
Argument Name Type In/Out Default?
------------------------------ ----------------------- ------ --------
SQL_HANDLE VARCHAR2 IN DEFAULT
PLAN_NAME VARCHAR2 IN DEFAULT
FORMAT VARCHAR2 IN DEFAULT
…
dbms_xplan.display
展示执行计划内容
简单的执行一次display
SQL> explain plan for insert into scott.emp values(1111,'xplan','','','','','','');
Explained.
SQL> select * from table(dbms_xplan.display);
7 rows selected.
Execution Plan
----------------------------------------------------------
Plan hash value: 2137789089
---------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
---------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 8168 | 16336 | 29 (0)| 00:00:01 |
| 1 | COLLECTION ITERATOR PICKLER FETCH| DISPLAY | 8168 | 16336 | 29 (0)| 00:00:01 |
---------------------------------------------------------------------------------------------
Statistics
----------------------------------------------------------
1890 recursive calls
40 db block gets
3635 consistent gets
0 physical reads
0 redo size
1102 bytes sent via SQL*Net to client
523 bytes received via SQL*Net from client
2 SQL*Net roundtrips to/from client
38 sorts (memory)
0 sorts (disk)
7 rows processed
SQL> select * from scott.emp where empno=1111;
no rows selected
-explain plan for ，dbms_xplan.display都没有执行sql。explain plan for是产生sql的执行计划并保存在PLAN_TABLE表中，dbms_xplan.display从PLAN_TABLE中提取计划并展示出来。
定义
DBMS_XPLAN.DISPLAY(
table_name IN VARCHAR2 DEFAULT 'PLAN_TABLE',
statement_id IN VARCHAR2 DEFAULT NULL,
format IN VARCHAR2 DEFAULT 'TYPICAL',
filter_preds IN VARCHAR2 DEFAULT NULL);
table_name：指定的是计划的存储表表名（不是执行表的表名）。默认是PLAN_TABLE。
statement_id：指定计划的statement_id，如果没有指定，则该值为explain plan的statement_id , 如果没有expain plan，则该值为最近一次解释的执行计划。
format：解释计划的level
? BASIC: Displays the minimum information in the plan-the operation ID, the operation name and its option.展示最少的信息
? TYPICAL: This is the default. Displays the most relevant information in the plan (operation id, name and option, #rows, #bytes and optimizer cost). Pruning, parallel and predicate information are only displayed when applicable. Excludes only PROJECTION, ALIAS and REMOTE SQL information (see below).默认值
? SERIAL: Like TYPICAL except that the parallel information is not displayed, even if the plan executes in parallel.没有并发信息
? ALL: Maximum user level. Includes information displayed with the TYPICAL level with additional information (PROJECTION, ALIAS and information about REMOTE SQL if the operation is distributed).展示最多的信息，包含了分布式操作的远程sql执行信息
filter_preds：sql过滤，限制从计划表中返回的行。
dbms_xplan.display_awr
展示在awr中存储的sql的执行计划
定义
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);
sql_id:在dba_hist_sqltext中可以找到sql_id
plan_hash_value:sql执行计划的hash值。如果该值被忽略，则函数返回sql_id中的所有执行计划
db_id：database_id。如果不知道则该值为V$DATABASE视图中的database_id，也就是本地数据库。
format：与display类似。总共有4个level：BASIC，TYPICAL,SERIAL,ALL。
SQL> select * from scott.emp where rownum<=1;
EMPNO ENAME JOB MGR HIREDATE SAL COMM
---------- ---------- --------- ---------- --------- ---------- ----------
DEPTNO
----------
7369 SMITH CLERK 7902 17-DEC-80 800
20
-手动生成快照
SQL> EXECUTE DBMS_WORKLOAD_REPOSITORY.CREATE_SNAPSHOT();
PL/SQL procedure successfully completed.
SQL> select sql_id,sql_text from dba_hist_sqltext where sql_text like '%rownum%';
SQL_ID
-------------
SQL_TEXT
--------------------------------------------------------------------------------
6yzbcy3x0yr1j
insert into wrh$_dispatcher (snap_id, dbid, instance_number, name, serial#,
fsbqktj5vw6n9
select next_run_date, obj#, run_job, sch_job from (select decode(bitand(a.flags,
cv959u044n88s
select 1 from sys.aq$_subscriber_table where rownum < 2 and subscriber_id <> 0 a
…
SQL_ID
-------------
SQL_TEXT
--------------------------------------------------------------------------------
bd3tcy3ar02px
select * from scott.emp where rownum<=1
7 rows selected.
SQL>
-指定awr中存在sql
SQL> select * from table(dbms_xplan.display_awr('bd3tcy3ar02px'));
PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------------
SQL_ID bd3tcy3ar02px
--------------------
select * from scott.emp where rownum<=1
Plan hash value: 1973284518
---------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
---------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | | | 2 (100)| |
| 1 | COUNT STOPKEY | | | | | |
PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------------
| 2 | TABLE ACCESS FULL| EMP | 15 | 1305 | 2 (0)| 00:00:01 |
---------------------------------------------------------------------------
Note
-----
- dynamic sampling used for this statement (level=2)
18 rows selected.
SQL>
dbms_xplan.display_cursor
展示cursor中的执行计划
定义
DBMS_XPLAN.DISPLAY_CURSOR(
sql_id IN VARCHAR2 DEFAULT NULL,
cursor_child_no IN NUMBER DEFAULT 0,
format IN VARCHAR2 DEFAULT 'TYPICAL');
sql_id
cursor_child_no:子游标标志。如果没有指定，则展示sql_id下的所有执行计划
format
默认值执行
SQL> select * from scott.emp where rownum<=2;
EMPNO ENAME JOB MGR HIREDATE SAL COMM
---------- ---------- --------- ---------- --------- ---------- ----------
DEPTNO
----------
7369 SMITH CLERK 7902 17-DEC-80 800
20
7499 ALLEN SALESMAN 7698 20-FEB-81 1600 300
30
-默认查询了当前session最后一次执行sql
SQL> select * from table(dbms_xplan.display_cursor);
PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------------
SQL_ID 90ud69jbjz75c, child number 0
-------------------------------------
select * from scott.emp where rownum<=2
Plan hash value: 1973284518
---------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
---------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | | | 2 (100)| |
|* 1 | COUNT STOPKEY | | | | | |
PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------------
| 2 | TABLE ACCESS FULL| EMP | 15 | 1305 | 2 (0)| 00:00:01 |
---------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
1 - filter(ROWNUM<=2)
Note
-----
- dynamic sampling used for this statement (level=2)
PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------------
23 rows selected.
SQL>
指定sql_id查找plan，首先要找到sql_id
SQL> select sql_id,sql_text from v$sqlarea where sql_text like '%rownum<=2%';
SQL_ID
-------------
SQL_TEXT
--------------------------------------------------------------------------------
75gpskbx0uk8w
select sql_id,sql_text from v$sqlarea where sql_text like '%rownum<=2%'
90ud69jbjz75c
select * from scott.emp where rownum<=2
SQL> select * from table(dbms_xplan.display_cursor('90ud69jbjz75c'));
PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------------
SQL_ID 90ud69jbjz75c, child number 0
-------------------------------------
select * from scott.emp where rownum<=2
Plan hash value: 1973284518
---------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
---------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | | | 2 (100)| |
|* 1 | COUNT STOPKEY | | | | | |
PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------------
| 2 | TABLE ACCESS FULL| EMP | 15 | 1305 | 2 (0)| 00:00:01 |
---------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
1 - filter(ROWNUM<=2)
Note
-----
- dynamic sampling used for this statement (level=2)
PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------------
23 rows selected.
SQL>
如果sql不在内存中，则不能通过cursor方式查询
SQL> select * from table(dbms_xplan.display_cursor('90ud69jbjz75c'));
PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------------
SQL_ID: 90ud69jbjz75c, child number: 0 cannot be found
这时就可以通过生成快照的方式从awr中查询plan
以上是"如何使用dbms_xplan查看执行计划"这篇文章的所有内容，感谢各位的阅读！相信大家都有了一定的了解，希望分享的内容对大家有所帮助，如果还想学习更多知识，欢迎关注行业资讯频道！
