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Oracle中使用DBMS_XPLAN處理執(zhí)行計劃詳解

DBMS_XPLAN是Oracle提供的一個用于查看SQL計劃，包括執(zhí)行計劃和解釋計劃的包；在以前查看SQL執(zhí)行計劃的時候，我都是使用set autotrace命令，不過現(xiàn)在看來，DBMS_XPLAN包給出了更加簡化的獲取和顯示計劃的方式。

這5個函數(shù)分別對應(yīng)不同的顯示計劃的方式，DBMS_XPLAN包不僅可以獲取解釋計劃，它還可以用來輸出存儲在AWR，SQL調(diào)試集，緩存的SQL游標(biāo)，以及SQL基線中的語句計劃，實現(xiàn)如上的功能，通常會用到一下5個方法：

1.DISPLAY
2.DISPLAY_AWR
3.DISPLAY_CURSOR
4.DISPLAY_PLAN
5.DISPLAY_SQL_PLAN_BASELINE
6.DISPLAY_SQLSET

下面將重點討論關(guān)于DBMS_XPLAN包在解釋計劃和執(zhí)行計劃上的應(yīng)用。

來看一個經(jīng)常使用的查看某條語句的解釋計劃示例：

復(fù)制代碼代碼如下:

SQL> explain plan for select * from scott.emp;

Explained.

SQL> select * from table(dbms_xplan.display);

PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------------
Plan hash value: 3956160932

--------------------------------------------------------------------------
| Id | Operation         | Name | Rows | Bytes | Cost (%CPU)| Time     |
--------------------------------------------------------------------------
|   0 | SELECT STATEMENT |      |    14 |   532 |     3   (0)| 00:00:01 |
|   1 | TABLE ACCESS FULL| EMP |    14 |   532 |     3   (0)| 00:00:01 |
--------------------------------------------------------------------------

8 rows selected.

-- 對應(yīng)autotrace實現(xiàn)
SQL> set autotrace traceonly explain

上例中使用了dbms_xplan.display方法來顯示PLAN_TABLE中保存的解釋計劃，如果想要顯示執(zhí)行計劃，就需要使用到DMBS_XPLAN.DISPLAY_CURSOR方法了，DMBS_XPLAN.DISPLAY_CURSOR調(diào)用簽名：

復(fù)制代碼代碼如下:

DBMS_XPLAN.DISPLAY_CURSOR(

   sql_id        IN  VARCHAR2  DEFAULT  NULL,

   child_number  IN  NUMBER    DEFAULT  NULL,

   format        IN  VARCHAR2  DEFAULT  'TYPICAL');

sql_id表示存儲在cursor cache中的SQL語句的id，child_number用于指示緩存sql語句計劃的子id，format參數(shù)用于控制包含在輸出中的信息類型，官檔的參數(shù)如下：

1.BASIC: 顯示最少的信息，只包括操作類型，ID名稱和選項。
2.TYPICAL: 默認(rèn)值，顯示相關(guān)信息以及某些附加的顯示選項，如分區(qū)和并發(fā)使用等。
3.SERIAL: 與TYPICAL類型相似，區(qū)別是它不包括并發(fā)的信息，即使是并行執(zhí)行的計劃。
4.ALL: 顯示最多的信息，包含了TYPICAL的全部以及更多的附加信息,如別名和遠(yuǎn)程調(diào)用等。

除了以上的基本的四種輸出格式外，format還有一些附加的選項可用于定制化輸出行為，使用中可以通過逗號和空格分隔來聲明多個關(guān)鍵字，同時可以使用”+”和”-”符號來包含或排除相應(yīng)的顯示元素，這些附加的選項在官檔中也有記載：

1.ROWS – 顯示被優(yōu)化器估算的記錄的行號
2.BYTES – 顯示優(yōu)化器估算的字節(jié)數(shù)
3.COST – 顯示優(yōu)化器計算的成本信息
4.PARTITION – 顯示分區(qū)的分割信息
5.PARALLEL – 顯示并行執(zhí)行信息
6.PREDICATE – 顯示謂語
7.PROJECTION – 顯示列投影部分(每一行的那些列被傳遞給其父列已經(jīng)這些列的大小)
8.ALIAS – 顯示查詢塊名稱已經(jīng)對象別名
9.REMOTE – 顯示分布式查詢信息
10.NOTE – 顯示注釋
11.IOSTATS – 顯示游標(biāo)執(zhí)行的IO統(tǒng)計信息
12.MEMSTATS – 為內(nèi)存密集運算如散列聯(lián)結(jié)，排序，或一些類型的位圖運算顯示內(nèi)存管理統(tǒng)計信息
13.ALLSTATS – 與'IOSTATS MEMSTATS'等價
14.LAST – 顯示最后執(zhí)行的執(zhí)行計劃統(tǒng)計信息，默認(rèn)顯示為ALL類型，并且可以累積。

以上的參數(shù)同樣適用于解釋計劃的display方法。

示例部分：

一、使用display_cursor方法查看最近一條語句的執(zhí)行計劃

復(fù)制代碼代碼如下:

SQL> select /*+ gather_plan_statistics */ count(*) from scott.emp;

COUNT(*)
----------
14

SQL> select * from table(dbms_xplan.display_cursor(null,null,'ALLSTATS LAST'));

PLAN_TABLE_OUTPUT
-------------------------------------------------------------------------------------------------------
SQL_ID f9qyz8s3c2c02, child number 0
-------------------------------------
select /*+ gather_plan_statistics */ count(*) from scott.emp

Plan hash value: 2937609675

-------------------------------------------------------------------------------------
| Id | Operation        | Name   | Starts | E-Rows | A-Rows |   A-Time   | Buffers |
-------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT |        |      1 |        |      1 |00:00:00.01 |       1 |
|   1 | SORT AGGREGATE |        |      1 |      1 |      1 |00:00:00.01 |       1 |
|   2 |   INDEX FULL SCAN| PK_EMP |      1 |     14 |     14 |00:00:00.01 |       1 |
-------------------------------------------------------------------------------------

14 rows selected.

使用dbms_xplan.display_cursor(null,null,'ALLSTATS LAST')時，將sql_id和child_number設(shè)置成null，表示獲取上一條執(zhí)行語句的執(zhí)行計劃；注意上面的例子中一定要指定gather_plan_statistics提示或者手動設(shè)置數(shù)據(jù)庫STATISTICS_LEVEL參數(shù)為ALL來使得其抓取行數(shù)據(jù)源的執(zhí)行統(tǒng)計信息，這些信息包括行數(shù)，一直讀取次數(shù)，物理讀次數(shù)，物理寫次數(shù)以及運算在一行數(shù)據(jù)上耗費的運行時間，如果沒有指定該提示，就不會有A-Rows,A-Time,Buffers這三列信息。

二、獲取某條指定語句的執(zhí)行計劃

復(fù)制代碼代碼如下:

SQL> select /*+ gather_plan_statistics */ count(*) from hr.employees where department_id in (90, 100);

COUNT(*)
----------
9

-- 通過v$sql視圖查詢到sql語句的SQL_ID和CHILD_NUMBER
SQL> select sql_id,child_number,sql_text from v$sql
2 where sql_text like '%select /*+ gather_plan_statistics */ count(*)%';

SQL_ID        CHILD_NUMBER SQL_TEXT
------------- ------------ ----------------------------------------------------------------------------------------------------
5qxmkvh40yw0p            0 select /*+ gather_plan_statistics */ count(*) from hr.employees where department_id in (90, 100)
bqjrnskvpv51n            0 select sql_id,child_number,sql_text from v$sql where sql_text like '%select /*+ gather_plan_statisti
                           cs */ count(*)%'

-- 獲取對應(yīng)的執(zhí)行計劃
SQL> select * from table(dbms_xplan.display_cursor('5qxmkvh40yw0p',0,'ALLSTATS LAST'));

PLAN_TABLE_OUTPUT
----------------------------------------------------------------------------------------------------
SQL_ID 5qxmkvh40yw0p, child number 0
-------------------------------------
select /*+ gather_plan_statistics */ count(*) from hr.employees where
department_id in (90, 100)

Plan hash value: 4167091351

--------------------------------------------------------------------------------------------------
| Id | Operation          | Name              | Starts | E-Rows | A-Rows |   A-Time   | Buffers |
--------------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT   |                   |      1 |        |      1 |00:00:00.01 |       2 |
|   1 | SORT AGGREGATE    |                   |      1 |      1 |      1 |00:00:00.01 |       2 |
|   2 |   INLIST ITERATOR |                   |      1 |        |      9 |00:00:00.01 |       2 |
|* 3 |    INDEX RANGE SCAN| EMP_DEPARTMENT_IX |      2 |      9 |      9 |00:00:00.01 |       2 |
--------------------------------------------------------------------------------------------------

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

3 - access(("DEPARTMENT_ID"=90 OR "DEPARTMENT_ID"=100))

21 rows selected.

三、通過format參數(shù)定制執(zhí)行計劃輸出信息

復(fù)制代碼代碼如下:

-- 使用ALL來顯示解釋計劃的全部信息
SQL> explain plan for
2 select * from emp e, dept d
3 where e.deptno = d.deptno
4 and e.ename = 'JONES' ;

Explained.

SQL> select * from table(dbms_xplan.display(format=>'ALL'));

PLAN_TABLE_OUTPUT
----------------------------------------------------------------------------------------------------
Plan hash value: 3625962092

----------------------------------------------------------------------------------------
| Id | Operation                    | Name    | Rows | Bytes | Cost (%CPU)| Time     |
----------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT             |         |     1 |    58 |     4   (0)| 00:00:01 |
|   1 | NESTED LOOPS                |         |       |       |            |          |
|   2 |   NESTED LOOPS               |         |     1 |    58 |     4   (0)| 00:00:01 |
|* 3 |    TABLE ACCESS FULL         | EMP     |     1 |    38 |     3   (0)| 00:00:01 |
|* 4 |    INDEX UNIQUE SCAN         | PK_DEPT |     1 |       |     0   (0)| 00:00:01 |
|   5 |   TABLE ACCESS BY INDEX ROWID| DEPT    |     1 |    20 |     1   (0)| 00:00:01 |

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

   1 - SEL$1
   3 - SEL$1 / E@SEL$1
   4 - SEL$1 / D@SEL$1
   5 - SEL$1 / D@SEL$1

Predicate Information (identified by operation id):

3 - filter("E"."ENAME"='JONES')
4 - access("E"."DEPTNO"="D"."DEPTNO")

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

   1 - (#keys=0) "E"."EMPNO"[NUMBER,22], "E"."ENAME"[VARCHAR2,10],
       "E"."JOB"[VARCHAR2,9], "E"."MGR"[NUMBER,22], "E"."HIREDATE"[DATE,7],
       "E"."SAL"[NUMBER,22], "E"."COMM"[NUMBER,22], "E"."DEPTNO"[NUMBER,22],
       "D"."DEPTNO"[NUMBER,22], "D"."DNAME"[VARCHAR2,14], "D"."LOC"[VARCHAR2,13]
   2 - (#keys=0) "E"."EMPNO"[NUMBER,22], "E"."ENAME"[VARCHAR2,10],
       "E"."JOB"[VARCHAR2,9], "E"."MGR"[NUMBER,22], "E"."HIREDATE"[DATE,7],
       "E"."SAL"[NUMBER,22], "E"."COMM"[NUMBER,22], "E"."DEPTNO"[NUMBER,22],
       "D".ROWID[ROWID,10], "D"."DEPTNO"[NUMBER,22]
   3 - "E"."EMPNO"[NUMBER,22], "E"."ENAME"[VARCHAR2,10], "E"."JOB"[VARCHAR2,9],
       "E"."MGR"[NUMBER,22], "E"."HIREDATE"[DATE,7], "E"."SAL"[NUMBER,22],
       "E"."COMM"[NUMBER,22], "E"."DEPTNO"[NUMBER,22]
   4 - "D".ROWID[ROWID,10], "D"."DEPTNO"[NUMBER,22]
   5 - "D"."DNAME"[VARCHAR2,14], "D"."LOC"[VARCHAR2,13]

43 rows selected.

-- 去除執(zhí)行計劃上的字節(jié)數(shù)和成本統(tǒng)計信息
SQL> select empno, ename from emp e, dept d
2 where e.deptno = d.deptno
3 and e.ename = 'JONES' ;

EMPNO ENAME
---------- ----------
7566 JONES

SQL> select * from table(dbms_xplan.display_cursor(null,null,format=>'ALLSTATS LAST -COST -BYTES'));

PLAN_TABLE_OUTPUT
----------------------------------------------------------------------------------------------------
SQL_ID 3mypf7d6npa97, child number 1
-------------------------------------
select empno, ename from emp e, dept d where e.deptno = d.deptno and
e.ename = 'JONES'

Plan hash value: 3956160932

------------------------------------------------------------------------------------
| Id | Operation         | Name | Starts | E-Rows | A-Rows |   A-Time   | Buffers |
------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT |      |      1 |        |      1 |00:00:00.01 |       8 |
|* 1 | TABLE ACCESS FULL| EMP |      1 |      1 |      1 |00:00:00.01 |       8 |
------------------------------------------------------------------------------------

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

1 - filter(("E"."ENAME"='JONES' AND "E"."DEPTNO" IS NOT NULL))

19 rows selected.

-- 另一種選項，窺視綁定變量的值，非常方便??！
SQL> variable v_empno number
SQL> exec :v_empno := 7566 ;

PL/SQL procedure successfully completed.

SQL> select * from emp where empno = :v_empno ;

EMPNO ENAME JOB MGR HIREDATE SAL COMM DEPTNO
---------- ---------- --------- ---------- --------- ---------- ---------- ----------
7566 JONES MANAGER 7839 02-APR-81 2975 20

SQL> select * from table(dbms_xplan.display_cursor(null,null,format=>'+PEEKED_BINDS'));

PLAN_TABLE_OUTPUT
----------------------------------------------------------------------------------------------------
SQL_ID 9q17w9umt58m7, child number 0
-------------------------------------
select * from emp where empno = :v_empno

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)|          |
--------------------------------------------------------------------------------------

Peeked Binds (identified by position):
--------------------------------------

1 - :V_EMPNO (NUMBER): 7566

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

PLAN_TABLE_OUTPUT
----------------------------------------------------------------------------------------------------
2 - access("EMPNO"=:V_EMPNO)

24 rows selected.

-- 并行查詢信息篩選
SQL> select /*+ parallel(d, 4) parallel (e, 4) */
2 d.dname, avg(e.sal), max(e.sal)
3 from dept d, emp e
4 where d.deptno = e.deptno
5 group by d.dname
6 order by max(e.sal), avg(e.sal) desc;

DNAME          AVG(E.SAL) MAX(E.SAL)
-------------- ---------- ----------
SALES          1566.66667       2850
RESEARCH             2175       3000
ACCOUNTING     2916.66667       5000

SQL> select * from table(dbms_xplan.display_cursor(null,null,'TYPICAL -BYTES -COST'));

PLAN_TABLE_OUTPUT
----------------------------------------------------------------------------------------------------
SQL_ID gahr597f78j0d, child number 0
-------------------------------------
select /*+ parallel(d, 4) parallel (e, 4) */ d.dname, avg(e.sal),
max(e.sal) from dept d, emp e where d.deptno = e.deptno group by
d.dname order by max(e.sal), avg(e.sal) desc

Plan hash value: 3078011448

PLAN_TABLE_OUTPUT
----------------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT              |          |       |          |        |      |            |
|   1 | PX COORDINATOR               |          |       |          |        |      |            |
|   2 |   PX SEND QC (ORDER)          | :TQ10004 |     4 | 00:00:01 | Q1,04 | P->S | QC (ORDER) |
|   3 |    SORT ORDER BY              |          |     4 | 00:00:01 | Q1,04 | PCWP |            |
|   4 |     PX RECEIVE                |          |     4 | 00:00:01 | Q1,04 | PCWP |            |
|   5 |      PX SEND RANGE            | :TQ10003 |     4 | 00:00:01 | Q1,03 | P->P | RANGE      |
|   6 |       HASH GROUP BY           |          |     4 | 00:00:01 | Q1,03 | PCWP |            |
|   7 |        PX RECEIVE             |          |    14 | 00:00:01 | Q1,03 | PCWP |            |
|   8 |         PX SEND HASH          | :TQ10002 |    14 | 00:00:01 | Q1,02 | P->P | HASH       |
|* 9 |          HASH JOIN BUFFERED   |          |    14 | 00:00:01 | Q1,02 | PCWP |            |
| 10 |           PX RECEIVE          |          |     4 | 00:00:01 | Q1,02 | PCWP |            |
| 11 |            PX SEND HASH       | :TQ10000 |     4 | 00:00:01 | Q1,00 | P->P | HASH       |
| 12 |             PX BLOCK ITERATOR |          |     4 | 00:00:01 | Q1,00 | PCWC |            |
|* 13 |              TABLE ACCESS FULL| DEPT     |     4 | 00:00:01 | Q1,00 | PCWP |            |
| 14 |           PX RECEIVE          |          |    14 | 00:00:01 | Q1,02 | PCWP |            |
| 15 |            PX SEND HASH       | :TQ10001 |    14 | 00:00:01 | Q1,01 | P->P | HASH       |
| 16 |             PX BLOCK ITERATOR |          |    14 | 00:00:01 | Q1,01 | PCWC |            |
|* 17 |              TABLE ACCESS FULL| EMP      |    14 | 00:00:01 | Q1,01 | PCWP |            |
--------------------------------------------------------------------------------------------------

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

9 - access("D"."DEPTNO"="E"."DEPTNO")
13 - access(:Z>=:Z AND :Z=:Z) 17 - access(:Z>=:Z AND :Z=:Z)

38 rows selected.

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