Oracle SQL 执行计划

解释计划

语句EXPLAIN PLAN 用来显示优化器为SQL语句选择的执行计划。将估计的信息称为解释计划输出，把实际信息称为执行计划输出。以此区分实际的和预期的执行计划。

使用解释计划

当使用EXPLAIN来为查询生成预期的执行计划时，输出将包括以下几种：

• SQL语句中所引用到的每一张表。
• 访问每张表所用的方法。
• 每一对需要联结的数据源所用的联结方法。
• 按次序列出的所有需要完成的运算。
• 计划中各步骤的谓语信息列表。
• 对于每个运算，估计出该步骤所要操作的数据行数和字节数。
• 对于每个运算，计算出成本值。
• 如果适合，所访问的分区信息。
• 如果适用，并行执行的相关信息。

hr@orclpdb1:orclcdb> explain plan for
  2  select e.last_name || ', '||e.first_name as full_name,
  3         e.phone_number, e.email, e.department_id,
  4         d.department_name, c.country_name,l.city,l.state_province,
  5         r.region_name
  6    from hr.employees e, hr.departments d, hr.countries c,
  7         hr.locations l, hr.regions r
  8    where e.department_id = d.department_id
  9      and d.location_id = l.location_id
 10      and l.country_id = c.country_id
 11      and c.region_id = r.region_id;

Explained.
hr@orclpdb1:orclcdb> select * from table(dbms_xplan.display(format=>'BASIC+COST+PREDICATE'));

PLAN_TABLE_OUTPUT
----------------------------------------------------------------------------------------------------
Error: format 'BASIC+COST+PREDICATE' not valid for DBMS_XPLAN.DISPLAY()

1 row selected.

hr@orclpdb1:orclcdb>

1.2 PLAN_TABLE

解释计划输出中所看到的信息是由EXPLAIN PLAN命令生成并默认存储在表PLAN_TABLE中的。AUTOTRACE命令从所提供的dbms_xplan包中调用display函数来自动生成输出。当使用EXPLAIN PLAN命令时你必须手工执行查询。

PLAN_TABLE表

hr@orclpdb1:orclcdb> desc plan_table
 Name                                                  Null?    Type
 ----------------------------------------------------- -------- ------------------------------------
 STATEMENT_ID                                                   VARCHAR2(30)
 PLAN_ID                                                        NUMBER
 TIMESTAMP                                                      DATE
 REMARKS                                                        VARCHAR2(4000)
 OPERATION                                                      VARCHAR2(30)
 OPTIONS                                                        VARCHAR2(255)
 OBJECT_NODE                                                    VARCHAR2(128)
 OBJECT_OWNER                                                   VARCHAR2(128)
 OBJECT_NAME                                                    VARCHAR2(128)
 OBJECT_ALIAS                                                   VARCHAR2(261)
 OBJECT_INSTANCE                                                NUMBER(38)
 OBJECT_TYPE                                                    VARCHAR2(30)
 OPTIMIZER                                                      VARCHAR2(255)
 SEARCH_COLUMNS                                                 NUMBER
 ID                                                             NUMBER(38)
 PARENT_ID                                                      NUMBER(38)
 DEPTH                                                          NUMBER(38)
 POSITION                                                       NUMBER(38)
 COST                                                           NUMBER(38)
 CARDINALITY                                                    NUMBER(38)
 BYTES                                                          NUMBER(38)
 OTHER_TAG                                                      VARCHAR2(255)
 PARTITION_START                                                VARCHAR2(255)
 PARTITION_STOP                                                 VARCHAR2(255)
 PARTITION_ID                                                   NUMBER(38)
 OTHER                                                          LONG
 OTHER_XML                                                      CLOB
 DISTRIBUTION                                                   VARCHAR2(30)
 CPU_COST                                                       NUMBER(38)
 IO_COST                                                        NUMBER(38)
 TEMP_SPACE                                                     NUMBER(38)
 ACCESS_PREDICATES                                              VARCHAR2(4000)
 FILTER_PREDICATES                                              VARCHAR2(4000)
 PROJECTION                                                     VARCHAR2(4000)
 TIME                                                           NUMBER(38)
 QBLOCK_NAME                                                    VARCHAR2(128)

hr@orclpdb1:orclcdb> 

1.3 分解计划

在学习如何阅读计划输出时，理解计划是如何组织的非常重要。

只有一个子运算的运算可以分为以下3类：

• 加工运算   从子运算接收一个数据行集并经过加工以后传递给其父运算。
• 传递运算 只是起传递的作用而不对来自子运算的数据做任何修改或加工。它们基本上是用来确定某个运算的特性。
• 迭代运算  表示子运算要多次执行。

1.4 导致解释计划未达目的的原因

使用解释计划时有以下3点可能导致计划输出与实际执行计划不一致，请谨记：

• 解释计划是基于你使用它的时候的环境来生成的。
• 解释计划不考虑绑定变量的数据类型。
• 解释计划不“窥视”绑定变量的值。
• EXPLAIN PLAN只显示原始计划而并不显示最终的计划。

1.5 阅读计划

有3种途径有助于你阅读和理解所有计划：

• 学会识别和分割父子组。
• 掌握计划中运算执行的顺序。
• 学会以叙述的形式阅读计划。

2 执行计划

2.1 查看最近生成的SQL语句

scott@orclpdb1:orclcdb> select /*recentsql*/ sql_id,child_number,
  2                       hash_value,address,executions,sql_text
  3                     from v$sql
  4                     where parsing_user_id = (select user_id
  5                                               from all_users
  6                                              where username = 'SCOTT')
  7                     and command_type in (2,3,6,7,189)
  8                     and UPPER(sql_text) not like UPPER('%recentsql%');

SQL_ID        CHILD_NUMBER HASH_VALUE ADDRESS          EXECUTIONS
------------- ------------ ---------- ---------------- ----------
SQL_TEXT
----------------------------------------------------------------------------------------------------
711b9thj3s4ug            2  574362447 0000000072F829B8          3
SELECT /* DS_SVC */ /*+ dynamic_sampling(0) no_sql_tune no_monitoring optimizer_features_enable(defa
ult) no_parallel  */ NVL(C1,0), NVL(C2,0), NVL(C3,0) FROM (SELECT /*+ qb_name("innerQuery") NO_INDEX
_FFS( "O2")  */ 4294967295 AS C1, COUNT(*) AS C2, SUM(CASE WHEN ("O2"."TYPE#"=88) THEN 1 ELSE 0 END)
 AS C3  FROM "SYS"."OBJ$" SAMPLE BLOCK(32.76, 8) SEED(2)  "O2" WHERE ("O2"."TYPE#"=88)) innerQuery

8h0w3cbh1sj17            0 3759948839 0000000065ED5AC8          4
SELECT /* DS_SVC */ /*+ dynamic_sampling(0) no_sql_tune no_monitoring optimizer_features_enable(defa
ult) no_parallel  */ NVL(C1,0), NVL(C2,0), NVL(C3,0) FROM (SELECT /*+ qb_name("innerQuery") NO_INDEX
_FFS( "DO")  */ 4294967295 AS C1, COUNT(*) AS C2, SUM(CASE WHEN ("DO"."TYPE#"=92) THEN 1 ELSE 0 END)
 AS C3  FROM "SYS"."OBJ$" SAMPLE BLOCK(32.76, 8) SEED(2)  "DO" WHERE ("DO"."TYPE#"=92)) innerQuery

cvxurqu0r4p9s            0 2171753784 0000000063190D20          2
SELECT /* DS_SVC */ /*+ dynamic_sampling(0) no_sql_tune no_monitoring optimizer_features_enable(defa
ult) no_parallel  */ NVL(C1,0), NVL(C2,0), NVL(C3,0) FROM (SELECT /*+ qb_name("innerQuery") NO_INDEX
_FFS( "O")  */ 4294967295 AS C1, COUNT(*) AS C2, SUM(CASE WHEN ("O"."LINKNAME" IS NULL) AND ("O"."NA
ME"<>'_NEXT_OBJECT') AND ("O"."NAME"<>'_default_auditing_options_') THEN 1 ELSE 0 END) AS C3  FROM "
SYS"."OBJ$" SAMPLE BLOCK(32.76, 8) SEED(1)  "O" WHERE ("O"."LINKNAME" IS NULL)) innerQuery

2fnu4swc94x56            0  412251302 0000000065D7BF08          2
SELECT /* DS_SVC */ /*+ dynamic_sampling(0) no_sql_tune no_monitoring optimizer_features_enable(defa
ult) no_parallel  */ NVL(C1,0), NVL(C2,0), NVL(C3,0) FROM (SELECT /*+ qb_name("innerQuery") NO_INDEX
_FFS( "O")  */ 4294967295 AS C1, COUNT(*) AS C2, SUM(CASE WHEN ("O"."TYPE#"=9) THEN 1 ELSE 0 END) AS
 C3  FROM "SYS"."OBJ$" SAMPLE BLOCK(34.0704, 8) SEED(3)  "O" WHERE ("O"."TYPE#"=9)) innerQuery

1vcptyw64539d            0  205688109 000000006D901D10          4
SELECT /* DS_SVC */ /*+ dynamic_sampling(0) no_sql_tune no_monitoring optimizer_features_enable(defa
ult) no_parallel  */ NVL(C1,0), NVL(C2,0), NVL(C3,0) FROM (SELECT /*+ qb_name("innerQuery") NO_INDEX
_FFS( "IO")  */ 4294967295 AS C1, COUNT(*) AS C2, SUM(CASE WHEN ("IO"."TYPE#"=2) THEN 1 ELSE 0 END)
AS C3  FROM "SYS"."OBJ$" SAMPLE BLOCK(34.0704, 8) SEED(3)  "IO" WHERE ("IO"."TYPE#"=2)) innerQuery

a85aszwrrx49p            0  796823861 000000006BEE0498          3
SELECT /* DS_SVC */ /*+ dynamic_sampling(0) no_sql_tune no_monitoring optimizer_features_enable(defa
ult) no_parallel  */ NVL(C1,0), NVL(C2,0), NVL(C3,0) FROM (SELECT /*+ qb_name("innerQuery") NO_INDEX
_FFS( "OA")  */ 4294967295 AS C1, COUNT(*) AS C2, SUM(CASE WHEN ("OA"."PRIVILEGE#"=26) THEN 1 ELSE 0
 END) AS C3  FROM "SYS"."OBJAUTH$" "OA" WHERE ("OA"."PRIVILEGE#"=26)) innerQuery

dfrr3t49vdg23            0  330742851 000000006BA7A5E8          2
SELECT /* DS_SVC */ /*+ dynamic_sampling(0) no_sql_tune no_monitoring optimizer_features_enable(defa
ult) no_parallel  */ NVL(C1,0), NVL(C2,0), NVL(C3,0) FROM (SELECT /*+ qb_name("innerQuery") NO_INDEX
_FFS( "O")  */ 4294967295 AS C1, COUNT(*) AS C2, SUM(CASE WHEN ("O"."TYPE#"=13) THEN 1 ELSE 0 END) A
S C3  FROM "SYS"."OBJ$" SAMPLE BLOCK(32.76, 8) SEED(1)  "O" WHERE ("O"."TYPE#"=13)) innerQuery

4brf4vrw4tman            0 4165782868 0000000065ABB880          4
SELECT /* DS_SVC */ /*+ dynamic_sampling(0) no_sql_tune no_monitoring optimizer_features_enable(defa
ult) no_parallel  */ NVL(C1,0), NVL(C2,0), NVL(C3,0) FROM (SELECT /*+ qb_name("innerQuery") NO_INDEX
_FFS( "DO")  */ 4294967295 AS C1, COUNT(*) AS C2, SUM(CASE WHEN ("DO"."TYPE#"=92) THEN 1 ELSE 0 END)
 AS C3  FROM "SYS"."OBJ$" SAMPLE BLOCK(34.0704, 8) SEED(3)  "DO" WHERE ("DO"."TYPE#"=92)) innerQuery

gtcj3hs72xnb0            0  237949280 000000006DBCF5A0          2
SELECT /* DS_SVC */ /*+ dynamic_sampling(0) no_sql_tune no_monitoring optimizer_features_enable(defa
ult) no_parallel  */ NVL(C1,0), NVL(C2,0), NVL(C3,0) FROM (SELECT /*+ qb_name("innerQuery") NO_INDEX
_FFS( "O")  */ 4294967295 AS C1, COUNT(*) AS C2, SUM(CASE WHEN ("O"."TYPE#"=13) THEN 1 ELSE 0 END) A
S C3  FROM "SYS"."OBJ$" SAMPLE BLOCK(32.76, 8) SEED(2)  "O" WHERE ("O"."TYPE#"=13)) innerQuery

0j5t5v01p1u1f            0   55633966 0000000065599EB8          2
SELECT /* DS_SVC */ /*+ dynamic_sampling(0) no_sql_tune no_monitoring optimizer_features_enable(defa
ult) no_parallel  */ NVL(C1,0), NVL(C2,0), NVL(C3,0) FROM (SELECT /*+ qb_name("innerQuery") NO_INDEX
_FFS( "O")  */ 4294967295 AS C1, COUNT(*) AS C2, SUM(CASE WHEN ("O"."LINKNAME" IS NULL) AND ("O"."NA
ME"<>'_NEXT_OBJECT') AND ("O"."NAME"<>'_default_auditing_options_') THEN 1 ELSE 0 END) AS C3  FROM "
SYS"."OBJ$" SAMPLE BLOCK(32.76, 8) SEED(2)  "O" WHERE ("O"."LINKNAME" IS NULL)) innerQuery

grqh1qs9ajypn            2  313064116 000000006F23C3F8          3
SELECT /* DS_SVC */ /*+ dynamic_sampling(0) no_sql_tune no_monitoring optimizer_features_enable(defa
ult) no_parallel  */ NVL(C1,0), NVL(C2,0), NVL(C3,0) FROM (SELECT /*+ qb_name("innerQuery") NO_INDEX
_FFS( "O2")  */ 4294967295 AS C1, COUNT(*) AS C2, SUM(CASE WHEN ("O2"."TYPE#"=88) THEN 1 ELSE 0 END)
 AS C3  FROM "SYS"."OBJ$" SAMPLE BLOCK(32.76, 8) SEED(1)  "O2" WHERE ("O2"."TYPE#"=88)) innerQuery

64mytapbgu243            0 1459423363 00000000659558D0          4
SELECT /* DS_SVC */ /*+ dynamic_sampling(0) no_sql_tune no_monitoring optimizer_features_enable(defa
ult) no_parallel  */ NVL(C1,0), NVL(C2,0), NVL(C3,0) FROM (SELECT /*+ qb_name("innerQuery") NO_INDEX
_FFS( "IO")  */ 4294967295 AS C1, COUNT(*) AS C2, SUM(CASE WHEN ("IO"."TYPE#"=2) THEN 1 ELSE 0 END)
AS C3  FROM "SYS"."OBJ$" SAMPLE BLOCK(32.76, 8) SEED(1)  "IO" WHERE ("IO"."TYPE#"=2)) innerQuery

2hbqfbtu1a9qj            0 1947543249 0000000072793380          3
SELECT /* DS_SVC */ /*+ dynamic_sampling(0) no_sql_tune no_monitoring optimizer_features_enable(defa
ult) no_parallel  */ NVL(SUM(C1),0) FROM (SELECT /*+ qb_name("innerQuery") NO_INDEX_FFS( "OBJAUTH$")
  */ 1 AS C1 FROM "SYS"."OBJAUTH$" "OBJAUTH$" WHERE ("OBJAUTH$"."PRIVILEGE#"=9 OR "OBJAUTH$"."PRIVIL
EGE#"=17)) innerQuery

2hkj0am2paatk            0 3310693170 0000000068338768         13
SELECT /* DS_SVC */ /*+ dynamic_sampling(0) no_sql_tune no_monitoring optimizer_features_enable(defa
ult) no_parallel  */ NVL(SUM(C1),0) FROM (SELECT /*+ qb_name("innerQuery")  */ 1 AS C1 FROM "SYS"."X
$KZSRO" "X$KZSRO" WHERE ("X$KZSRO"."CON_ID"=0 OR "X$KZSRO"."CON_ID"=3)) innerQuery

599a02kw4qd73            0 3091936483 000000006B6BA218          2
SELECT /* DS_SVC */ /*+ dynamic_sampling(0) no_sql_tune no_monitoring optimizer_features_enable(defa
ult) no_parallel  */ NVL(C1,0), NVL(C2,0), NVL(C3,0) FROM (SELECT /*+ qb_name("innerQuery") NO_INDEX
_FFS( "O")  */ 4294967295 AS C1, COUNT(*) AS C2, SUM(CASE WHEN ("O"."TYPE#"=9) THEN 1 ELSE 0 END) AS
 C3  FROM "SYS"."OBJ$" SAMPLE BLOCK(32.76, 8) SEED(2)  "O" WHERE ("O"."TYPE#"=9)) innerQuery

2ab8q85k5uqkd            2 1683839565 0000000068F436A8          3
SELECT /* DS_SVC */ /*+ dynamic_sampling(0) no_sql_tune no_monitoring optimizer_features_enable(defa
ult) no_parallel  */ NVL(C1,0), NVL(C2,0), NVL(C3,0) FROM (SELECT /*+ qb_name("innerQuery") NO_INDEX
_FFS( "O2")  */ 4294967295 AS C1, COUNT(*) AS C2, SUM(CASE WHEN ("O2"."TYPE#"=88) THEN 1 ELSE 0 END)
 AS C3  FROM "SYS"."OBJ$" SAMPLE BLOCK(34.0704, 8) SEED(3)  "O2" WHERE ("O2"."TYPE#"=88)) innerQuery

5vmt9nkkpkr7f            0 2774097134 0000000071BCA670          4
SELECT /* DS_SVC */ /*+ dynamic_sampling(0) no_sql_tune no_monitoring optimizer_features_enable(defa
ult) no_parallel  */ NVL(C1,0), NVL(C2,0), NVL(C3,0) FROM (SELECT /*+ qb_name("innerQuery") NO_INDEX
_FFS( "DO")  */ 4294967295 AS C1, COUNT(*) AS C2, SUM(CASE WHEN ("DO"."TYPE#"=92) THEN 1 ELSE 0 END)
 AS C3  FROM "SYS"."OBJ$" SAMPLE BLOCK(32.76, 8) SEED(1)  "DO" WHERE ("DO"."TYPE#"=92)) innerQuery

8tjsfvqd872sr            1 2592312087 00000000659411D0          3
SELECT /* DS_SVC */ /*+ dynamic_sampling(0) no_sql_tune no_monitoring optimizer_features_enable(defa
ult) no_parallel  */ NVL(SUM(C1),0) FROM (SELECT /*+ qb_name("innerQuery") NO_INDEX_FFS( "OA")  */ 1
 AS C1 FROM "SYS"."OBJAUTH$" "OA" WHERE ("OA"."PRIVILEGE#"=26)) innerQuery

7nqh3a78933m5            0 3499200101 000000006DAADAB0          2
SELECT /* DS_SVC */ /*+ dynamic_sampling(0) no_sql_tune no_monitoring optimizer_features_enable(defa
ult) no_parallel  */ NVL(C1,0), NVL(C2,0), NVL(C3,0) FROM (SELECT /*+ qb_name("innerQuery") NO_INDEX
_FFS( "O")  */ 4294967295 AS C1, COUNT(*) AS C2, SUM(CASE WHEN ("O"."TYPE#"=9) THEN 1 ELSE 0 END) AS
 C3  FROM "SYS"."OBJ$" SAMPLE BLOCK(32.76, 8) SEED(1)  "O" WHERE ("O"."TYPE#"=9)) innerQuery

at7grrzkbr4rh            1 3837498096 000000006B5C2C88          3
SELECT LOWER(USER || '@' ||              SYS_CONTEXT('userenv', 'con_name') || ':' ||              S
YS_CONTEXT('userenv', 'instance_name')) X FROM dual

6u5zqzz2nm55c            0 3309933740 000000006B427340          3
SELECT DECODE(USER, 'XS$NULL',  XS_SYS_CONTEXT('XS$SESSION','USERNAME'), USER) FROM SYS.DUAL

2k4q6d465bm0n            0  206949396 000000006BBA5CC0          2
SELECT /* DS_SVC */ /*+ dynamic_sampling(0) no_sql_tune no_monitoring optimizer_features_enable(defa
ult) no_parallel  OPT_ESTIMATE(@"innerQuery", TABLE, "X$KZSRO#1", SCALE_ROWS=3) */ NVL(SUM(C1),0) FR
OM (SELECT /*+ qb_name("innerQuery") NO_INDEX_FFS( "OA#0")  */ 1 AS C1 FROM "SYS"."X$KZSRO" "X$KZSRO
#1", "SYS"."OBJAUTH$" "OA#0" WHERE ("OA#0"."PRIVILEGE#"=12 OR "OA#0"."PRIVILEGE#"=26) AND ("OA#0"."G
RANTEE#"="X$KZSRO#1"."KZSROROL") AND ("X$KZSRO#1"."CON_ID"=0 OR "X$KZSRO#1"."CON_ID"=3)) innerQuery

8pnc9umudrrdw            0 4108049852 0000000072792B20          2
SELECT /* DS_SVC */ /*+ dynamic_sampling(0) no_sql_tune no_monitoring optimizer_features_enable(defa
ult) no_parallel  */ NVL(SUM(C1),0) FROM (SELECT /*+ qb_name("innerQuery") NO_INDEX_FFS( "OA")  */ 1
 AS C1 FROM "SYS"."OBJAUTH$" "OA" WHERE ("OA"."PRIVILEGE#"=12 OR "OA"."PRIVILEGE#"=26)) innerQuery

4k6u4npmqms0m            0 1734991891 000000007163B3C8          4
SELECT /* DS_SVC */ /*+ dynamic_sampling(0) no_sql_tune no_monitoring optimizer_features_enable(defa
ult) no_parallel  */ NVL(C1,0), NVL(C2,0), NVL(C3,0) FROM (SELECT /*+ qb_name("innerQuery") NO_INDEX
_FFS( "IO")  */ 4294967295 AS C1, COUNT(*) AS C2, SUM(CASE WHEN ("IO"."TYPE#"=2) THEN 1 ELSE 0 END)
AS C3  FROM "SYS"."OBJ$" SAMPLE BLOCK(32.76, 8) SEED(2)  "IO" WHERE ("IO"."TYPE#"=2)) innerQuery


24 rows selected.

scott@orclpdb1:orclcdb> 

2.2 查看相关执行计划

使用dbms_xplan.display_cursor函数

scott@orclpdb1:orclcdb> select /*+gather_plan_statistics*/ empno,ename from SCOTT.emp where ename = 'KING';

     EMPNO ENAME
---------- ----------
      7839 KING

1 row selected.

scott@orclpdb1:orclcdb> set serveroutput off
scott@orclpdb1:orclcdb> 
scott@orclpdb1:orclcdb> select * from table(dbms_xplan.display_cursor(null,null,'ALLSTATS LAST'));

PLAN_TABLE_OUTPUT
----------------------------------------------------------------------------------------------------
SQL_ID  5qgz1p0cut7mx, child number 0

BEGIN DBMS_OUTPUT.DISABLE; END;

NOTE: cannot fetch plan for SQL_ID: 5qgz1p0cut7mx, CHILD_NUMBER: 0
      Please verify value of SQL_ID and CHILD_NUMBER;
      It could also be that the plan is no longer in cursor cache (check v$sql_plan)


8 rows selected.

scott@orclpdb1:orclcdb> select * from table(dbms_xplan.display_cursor(null,null,'ALLSTATS LAST'));

PLAN_TABLE_OUTPUT
----------------------------------------------------------------------------------------------------
SQL_ID  91kkkbx7bnw9j, child number 1
-------------------------------------
select * from table(dbms_xplan.display_cursor(null,null,'ALLSTATS
LAST'))

Plan hash value: 3713220770

---------------------------------------------------------------------
| Id  | Operation                         | Name           | E-Rows |
---------------------------------------------------------------------
|   0 | SELECT STATEMENT                  |                |        |
|   1 |  COLLECTION ITERATOR PICKLER FETCH| DISPLAY_CURSOR |      2 |
---------------------------------------------------------------------

Note
-----
   - statistics feedback used for this statement
   - Warning: basic plan statistics not available. These are only collected when:
       * hint 'gather_plan_statistics' is used for the statement or
       * parameter 'statistics_level' is set to 'ALL', at session or system level


21 rows selected.

scott@orclpdb1:orclcdb> 

使用没有gather_plan_statistics提示的dbms_xplan.display_cursor函数

scott@orclpdb1:orclcdb> select ename from SCOTT.emp where ename = 'KING';

ENAME
----------
KING

1 row selected.

scott@orclpdb1:orclcdb> select * from table(dbms_xplan.display_cursor(null,null,'ALLSTATS LAST'));

PLAN_TABLE_OUTPUT
----------------------------------------------------------------------------------------------------
SQL_ID  9ygfkgffb7nhh, child number 0
-------------------------------------
select ename from SCOTT.emp where ename = 'KING'

Plan hash value: 3956160932

-------------------------------------------
| Id  | Operation         | Name | E-Rows |
-------------------------------------------
|   0 | SELECT STATEMENT  |      |        |
|*  1 |  TABLE ACCESS FULL| EMP  |      1 |
-------------------------------------------

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

   1 - filter("ENAME"='KING')

Note
-----
   - Warning: basic plan statistics not available. These are only collected when:
       * hint 'gather_plan_statistics' is used for the statement or
       * parameter 'statistics_level' is set to 'ALL', at session or system level


24 rows selected.

scott@orclpdb1:orclcdb>

可以看到，出现了一个警告信息表明无法获取计划统计信息，并高速你如何来收集这些信息。

2.3 收集执行计划统计信息

v$SQL_PLAN_STATISTICS_ALL视图描述

scott@orclpdb1:orclcdb> desc v$sql_plan_statistics_all
 Name                                                  Null?    Type
 ----------------------------------------------------- -------- ------------------------------------
 ADDRESS                                                        RAW(8)
 HASH_VALUE                                                     NUMBER
 SQL_ID                                                         VARCHAR2(13)
 PLAN_HASH_VALUE                                                NUMBER
 FULL_PLAN_HASH_VALUE                                           NUMBER
 CHILD_ADDRESS                                                  RAW(8)
 CHILD_NUMBER                                                   NUMBER
 TIMESTAMP                                                      DATE
 OPERATION                                                      VARCHAR2(30)
 OPTIONS                                                        VARCHAR2(30)
 OBJECT_NODE                                                    VARCHAR2(40)
 OBJECT#                                                        NUMBER
 OBJECT_OWNER                                                   VARCHAR2(128)
 OBJECT_NAME                                                    VARCHAR2(128)
 OBJECT_ALIAS                                                   VARCHAR2(261)
 OBJECT_TYPE                                                    VARCHAR2(20)
 OPTIMIZER                                                      VARCHAR2(20)
 ID                                                             NUMBER
 PARENT_ID                                                      NUMBER
 DEPTH                                                          NUMBER
 POSITION                                                       NUMBER
 SEARCH_COLUMNS                                                 NUMBER
 COST                                                           NUMBER
 CARDINALITY                                                    NUMBER
 BYTES                                                          NUMBER
 OTHER_TAG                                                      VARCHAR2(35)
 PARTITION_START                                                VARCHAR2(64)
 PARTITION_STOP                                                 VARCHAR2(64)
 PARTITION_ID                                                   NUMBER
 OTHER                                                          VARCHAR2(4000)
 DISTRIBUTION                                                   VARCHAR2(20)
 CPU_COST                                                       NUMBER
 IO_COST                                                        NUMBER
 TEMP_SPACE                                                     NUMBER
 ACCESS_PREDICATES                                              VARCHAR2(4000)
 FILTER_PREDICATES                                              VARCHAR2(4000)
 PROJECTION                                                     VARCHAR2(4000)
 TIME                                                           NUMBER
 QBLOCK_NAME                                                    VARCHAR2(128)
 REMARKS                                                        VARCHAR2(4000)
 OTHER_XML                                                      CLOB
 EXECUTIONS                                                     NUMBER
 LAST_STARTS                                                    NUMBER
 STARTS                                                         NUMBER
 LAST_OUTPUT_ROWS                                               NUMBER
 OUTPUT_ROWS                                                    NUMBER
 LAST_CR_BUFFER_GETS                                            NUMBER
 CR_BUFFER_GETS                                                 NUMBER
 LAST_CU_BUFFER_GETS                                            NUMBER
 CU_BUFFER_GETS                                                 NUMBER
 LAST_DISK_READS                                                NUMBER
 DISK_READS                                                     NUMBER
 LAST_DISK_WRITES                                               NUMBER
 DISK_WRITES                                                    NUMBER
 LAST_ELAPSED_TIME                                              NUMBER
 ELAPSED_TIME                                                   NUMBER
 POLICY                                                         VARCHAR2(10)
 ESTIMATED_OPTIMAL_SIZE                                         NUMBER
 ESTIMATED_ONEPASS_SIZE                                         NUMBER
 LAST_MEMORY_USED                                               NUMBER
 LAST_EXECUTION                                                 VARCHAR2(10)
 LAST_DEGREE                                                    NUMBER
 TOTAL_EXECUTIONS                                               NUMBER
 OPTIMAL_EXECUTIONS                                             NUMBER
 ONEPASS_EXECUTIONS                                             NUMBER
 MULTIPASSES_EXECUTIONS                                         NUMBER
 ACTIVE_TIME                                                    NUMBER
 MAX_TEMPSEG_SIZE                                               NUMBER
 LAST_TEMPSEG_SIZE                                              NUMBER
 CON_ID                                                         NUMBER
 CON_DBID                                                       NUMBER

scott@orclpdb1:orclcdb> 

2.4 标识SQL语句以便以后取回计划

scott@orclpdb1:orclcdb> 
scott@orclpdb1:orclcdb> select /*KM-EMPTEST1*/ empno,ename
  2                       from emp
  3                     where job = 'MANAGER';

     EMPNO ENAME
---------- ----------
      7566 JONES
      7698 BLAKE
      7782 CLARK

3 rows selected.

scott@orclpdb1:orclcdb> select sql_id,child_number,sql_text
  2                       from v$sql
  3                     where sql_text like '%KM-EMPTEST1%';

SQL_ID        CHILD_NUMBER
------------- ------------
SQL_TEXT
----------------------------------------------------------------------------------------------------
dcwkjwrc1ssak            0
select sql_id,child_number,sql_text                      from v$sql                    where sql_tex
t like '%KM-EMPTEST1%'

7m34m0utxpy4a            0
select /*KM-EMPTEST1*/ empno,ename                      from emp                    where job = 'MAN
AGER'


2 rows selected.

scott@orclpdb1:orclcdb> 
scott@orclpdb1:orclcdb> select * from table(dbms_xplan.display_cursor('7m34m0utxpy4a',0,'ALLSTATS LAST'));

PLAN_TABLE_OUTPUT
----------------------------------------------------------------------------------------------------
SQL_ID  7m34m0utxpy4a, child number 0
-------------------------------------
select /*KM-EMPTEST1*/ empno,ename                      from emp
            where job = 'MANAGER'

Plan hash value: 3956160932

-------------------------------------------
| Id  | Operation         | Name | E-Rows |
-------------------------------------------
|   0 | SELECT STATEMENT  |      |        |
|*  1 |  TABLE ACCESS FULL| EMP  |      3 |
-------------------------------------------

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

   1 - filter("JOB"='MANAGER')

Note
-----
   - Warning: basic plan statistics not available. These are only collected when:
       * hint 'gather_plan_statistics' is used for the statement or
       * parameter 'statistics_level' is set to 'ALL', at session or system level


25 rows selected.

scott@orclpdb1:orclcdb>