[20170104]一条sql优化.txt

[20170104]一条sql优化.txt

--生产系统不明原因重启,看了1下,顺便看了前后的awr报表,发现一条语句,其实问题没什么,只不过这种现象在开发很普遍,做一点点记录.

1.环境:
xxxxxx> @ &r/ver1

PORT_STRING                    VERSION        BANNER
------------------------------ -------------- ----------------------------------------------------------------
x86_64/Linux 2.4.xx            10.2.0.4.0     Oracle Database 10g Enterprise Edition Release 10.2.0.4.0 - 64bi

$ cat gf3wvnjzfnysy.sql
SELECT DISTINCT dept_dict.dept_name, staff_vs_group.group_code
           FROM dept_dict, staff_dict, staff_vs_group
          WHERE (staff_dict.emp_no = staff_vs_group.emp_no)
            AND (staff_vs_group.group_code = dept_dict.dept_code)
            AND (staff_vs_group.group_class = '门诊医生');

xxxxxx> alter session set statistics_level=all;
Session altered.

xxxxxx> @ &r/dpc '' ''
PLAN_TABLE_OUTPUT
-------------------------------------
SQL_ID  07drst9ks3xjm, child number 0
-------------------------------------
SELECT DISTINCT dept_dict.dept_name, staff_vs_group.group_code            FROM dept_dict, staff_dict, staff_vs_group           WHERE (staff_dict.emp_no =
staff_vs_group.emp_no)             AND (staff_vs_group.group_code = dept_dict.dept_code)             AND (staff_vs_group.group_class = '门诊医生')
Plan hash value: 3073008191
-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------
| Id  | Operation               | Name                         | Starts | E-Rows |E-Bytes| Cost (%CPU)| E-Time   | A-Rows |   A-Time   | Buffers |  OMem |  1Mem | Used-Mem |
-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------
|   1 |  HASH UNIQUE            |                              |      1 |    781 | 35145 |     6  (34)| 00:00:01 |     63 |00:00:00.01 |     941 |   795K|   795K| 1187K (0)|
|   2 |   NESTED LOOPS          |                              |      1 |    781 | 35145 |     5  (20)| 00:00:01 |    915 |00:00:00.01 |     941 |       |       |          |
|*  3 |    HASH JOIN            |                              |      1 |    781 | 31240 |     5  (20)| 00:00:01 |    929 |00:00:00.01 |      10 |   877K|   877K| 1105K (0)|
|   4 |     INDEX FAST FULL SCAN| I_DEPT_DICT_D_NAME_CODE_IN_C |      1 |    425 |  8500 |     2   (0)| 00:00:01 |    432 |00:00:00.01 |       7 |       |       |          |
|*  5 |     INDEX RANGE SCAN    | PK_STAFF_VS_GROUP            |      1 |    781 | 15620 |     2   (0)| 00:00:01 |    943 |00:00:00.01 |       3 |       |       |          |
|*  6 |    INDEX UNIQUE SCAN    | PK_STAFF_DICT                |    929 |      1 |     5 |     0   (0)|          |    915 |00:00:00.01 |     931 |       |       |          |
-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Query Block Name / Object Alias (identified by operation id):
-------------------------------------------------------------
   1 - SEL$1
   4 - SEL$1 / DEPT_DICT@SEL$1
   5 - SEL$1 / STAFF_VS_GROUP@SEL$1
   6 - SEL$1 / STAFF_DICT@SEL$1
Predicate Information (identified by operation id):
---------------------------------------------------
   3 - access("STAFF_VS_GROUP"."GROUP_CODE"="DEPT_DICT"."DEPT_CODE")
   5 - access("STAFF_VS_GROUP"."GROUP_CLASS"='门诊医生')
   6 - access("STAFF_DICT"."EMP_NO"="STAFF_VS_GROUP"."EMP_NO")

--//逻辑读941,问题主要出在第2步执行的NESTED LOOPS,导致逻辑读上升.优化的问题是减少逻辑读,减少响应时间.
--//加入提示use_hash(STAFF_DICT).

$ cat gf3wvnjzfnysy.sql
SELECT /*+ use_hash(STAFF_DICT) */ DISTINCT dept_dict.dept_name, staff_vs_group.group_code
           FROM dept_dict, staff_dict, staff_vs_group
          WHERE (staff_dict.emp_no = staff_vs_group.emp_no)
            AND (staff_vs_group.group_code = dept_dict.dept_code)
            AND (staff_vs_group.group_class = '门诊医生');

xxxxxx> @ &r/dpc '' ''
PLAN_TABLE_OUTPUT
-------------------------------------
SQL_ID  c4mbqwykjp1n0, child number 0
-------------------------------------
SELECT /*+ use_hash(STAFF_DICT) */ DISTINCT dept_dict.dept_name, staff_vs_group.group_code            FROM dept_dict, staff_dict, staff_vs_group           WHERE
(staff_dict.emp_no = staff_vs_group.emp_no)             AND (staff_vs_group.group_code = dept_dict.dept_code)             AND (staff_vs_group.group_class =
'门诊医生')
Plan hash value: 1733666958
-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------
| Id  | Operation               | Name                         | Starts | E-Rows |E-Bytes| Cost (%CPU)| E-Time   | A-Rows |   A-Time   | Buffers |  OMem |  1Mem | Used-Mem |
-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------
|   1 |  HASH UNIQUE            |                              |      1 |    781 | 35145 |     9  (23)| 00:00:01 |     63 |00:00:00.01 |      23 |   795K|   795K| 1186K (0)|
|*  2 |   HASH JOIN             |                              |      1 |    781 | 35145 |     8  (13)| 00:00:01 |    915 |00:00:00.01 |      23 |   833K|   833K| 1139K (0)|
|*  3 |    HASH JOIN            |                              |      1 |    781 | 31240 |     5  (20)| 00:00:01 |    929 |00:00:00.01 |      10 |   877K|   877K| 1182K (0)|
|   4 |     INDEX FAST FULL SCAN| I_DEPT_DICT_D_NAME_CODE_IN_C |      1 |    425 |  8500 |     2   (0)| 00:00:01 |    432 |00:00:00.01 |       7 |       |       |          |
|*  5 |     INDEX RANGE SCAN    | PK_STAFF_VS_GROUP            |      1 |    781 | 15620 |     2   (0)| 00:00:01 |    943 |00:00:00.01 |       3 |       |       |          |
|   6 |    INDEX FAST FULL SCAN | PK_STAFF_DICT                |      1 |   3530 | 17650 |     3   (0)| 00:00:01 |   3544 |00:00:00.01 |      13 |       |       |          |
-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Query Block Name / Object Alias (identified by operation id):
-------------------------------------------------------------
   1 - SEL$1
   4 - SEL$1 / DEPT_DICT@SEL$1
   5 - SEL$1 / STAFF_VS_GROUP@SEL$1
   6 - SEL$1 / STAFF_DICT@SEL$1
Predicate Information (identified by operation id):
---------------------------------------------------
   2 - access("STAFF_DICT"."EMP_NO"="STAFF_VS_GROUP"."EMP_NO")
   3 - access("STAFF_VS_GROUP"."GROUP_CODE"="DEPT_DICT"."DEPT_CODE")
   5 - access("STAFF_VS_GROUP"."GROUP_CLASS"='门诊医生')

--//逻辑读下降到23,视乎优化完成.实际上如果你仔细看上面的sql,我个人现在对dinstinct很敏感,查询的字段是dept_dict.dept_name,
--//staff_vs_group.group_code. 而字段staff_vs_group.group_code与这个字段dept_dict.dept_code是一样的,很明显查询仅仅是1个
--//表dept_dict,经典的使用extists例子.参考连接:http://www.itpub.net/thread-2048496-1-1.html

--//可以想像开发如下写sql语句,把需要的表列出来,写成连接需要的条件,然后写出需要显示的字段,重复加一个distinct,ok解决问题.
--//正确的应该这样写.

$ cat gf3wvnjzfnysy.sql4
SELECT dept_dict.dept_name, dept_dict.dept_code
  FROM dept_dict
WHERE EXISTS (
          SELECT /*+  use_hash111(staff_vs_group  staff_dict) */1
            FROM staff_vs_group , staff_dict
           WHERE staff_vs_group.group_code = dept_dict.dept_code
             AND staff_vs_group.group_class = '门诊医生'
             AND staff_dict.emp_no = staff_vs_group.emp_no
             );

xxxxxx> @ &r/dpc '' ''
PLAN_TABLE_OUTPUT
-------------------------------------
SQL_ID  4mummndvnvj6m, child number 0
-------------------------------------
SELECT dept_dict.dept_name, dept_dict.dept_code   FROM dept_dict  WHERE EXISTS (           SELECT /*+  use_hash111(staff_vs_group  staff_dict) */1
FROM staff_vs_group , staff_dict            WHERE staff_vs_group.group_code = dept_dict.dept_code              AND staff_vs_group.group_class = '门诊医生'
     AND staff_dict.emp_no = staff_vs_group.emp_no              )
Plan hash value: 1139953391
---------------------------------------------------------------------------------------------------------------------------------------------------------------------------
| Id  | Operation             | Name                         | Starts | E-Rows |E-Bytes| Cost (%CPU)| E-Time   | A-Rows |   A-Time   | Buffers |  OMem |  1Mem | Used-Mem |
---------------------------------------------------------------------------------------------------------------------------------------------------------------------------
|*  1 |  HASH JOIN SEMI       |                              |      1 |      2 |    52 |     5  (20)| 00:00:01 |     63 |00:00:00.01 |     956 |   877K|   877K| 1111K (0)|
|   2 |   INDEX FAST FULL SCAN| I_DEPT_DICT_D_NAME_CODE_IN_C |      1 |    425 |  8500 |     2   (0)| 00:00:01 |    432 |00:00:00.01 |       7 |       |       |          |
|   3 |   VIEW                | VW_SQ_1                      |      1 |    781 |  4686 |     2   (0)| 00:00:01 |    929 |00:00:00.01 |     949 |       |       |          |
|   4 |    NESTED LOOPS       |                              |      1 |    781 | 19525 |     2   (0)| 00:00:01 |    929 |00:00:00.01 |     949 |       |       |          |
|*  5 |     INDEX RANGE SCAN  | PK_STAFF_VS_GROUP            |      1 |    781 | 15620 |     2   (0)| 00:00:01 |    943 |00:00:00.01 |       4 |       |       |          |
|*  6 |     INDEX UNIQUE SCAN | PK_STAFF_DICT                |    943 |      1 |     5 |     0   (0)|          |    929 |00:00:00.01 |     945 |       |       |          |
---------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Query Block Name / Object Alias (identified by operation id):
-------------------------------------------------------------
   1 - SEL$C772B8D1
   2 - SEL$C772B8D1 / DEPT_DICT@SEL$1
   3 - SEL$683B0107 / VW_SQ_1@SEL$7511BFD2
   4 - SEL$683B0107
   5 - SEL$683B0107 / STAFF_VS_GROUP@SEL$2
   6 - SEL$683B0107 / STAFF_DICT@SEL$2
Predicate Information (identified by operation id):
---------------------------------------------------
   1 - access("GROUP_CODE"="DEPT_DICT"."DEPT_CODE")
   5 - access("STAFF_VS_GROUP"."GROUP_CLASS"='门诊医生')
   6 - access("STAFF_DICT"."EMP_NO"="STAFF_VS_GROUP"."EMP_NO")

--//逻辑读956,有点高.加入提示/*+  use_hash(staff_vs_group  staff_dict) */

$ cat gf3wvnjzfnysy.sql4
SELECT dept_dict.dept_name, dept_dict.dept_code
  FROM dept_dict
WHERE EXISTS (
          SELECT /*+  use_hash(staff_vs_group  staff_dict) */1
            FROM staff_vs_group , staff_dict
           WHERE staff_vs_group.group_code = dept_dict.dept_code
             AND staff_vs_group.group_class = '门诊医生'
             AND staff_dict.emp_no = staff_vs_group.emp_no
             );

xxxxxx> @ &r/dpc '' ''
PLAN_TABLE_OUTPUT
-------------------------------------
SQL_ID  9jqqu3djrdgvg, child number 0
-------------------------------------
SELECT dept_dict.dept_name, dept_dict.dept_code   FROM dept_dict  WHERE EXISTS (           SELECT /*+  use_hash(staff_vs_group  staff_dict) */1             FROM
staff_vs_group , staff_dict            WHERE staff_vs_group.group_code = dept_dict.dept_code              AND staff_vs_group.group_class = '门诊医生'
AND staff_dict.emp_no = staff_vs_group.emp_no              )
Plan hash value: 335906791
-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------
| Id  | Operation               | Name                         | Starts | E-Rows |E-Bytes| Cost (%CPU)| E-Time   | A-Rows |   A-Time   | Buffers |  OMem |  1Mem | Used-Mem |
-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------
|*  1 |  HASH JOIN SEMI         |                              |      1 |      2 |    52 |     8  (13)| 00:00:01 |     63 |00:00:00.01 |      24 |   877K|   877K| 1166K (0)|
|   2 |   INDEX FAST FULL SCAN  | I_DEPT_DICT_D_NAME_CODE_IN_C |      1 |    425 |  8500 |     2   (0)| 00:00:01 |    432 |00:00:00.01 |       7 |       |       |          |
|   3 |   VIEW                  | VW_SQ_1                      |      1 |    781 |  4686 |     6  (17)| 00:00:01 |    929 |00:00:00.01 |      17 |       |       |          |
|*  4 |    HASH JOIN            |                              |      1 |    781 | 19525 |     6  (17)| 00:00:01 |    929 |00:00:00.01 |      17 |   972K|   972K| 1207K (0)|
|*  5 |     INDEX RANGE SCAN    | PK_STAFF_VS_GROUP            |      1 |    781 | 15620 |     2   (0)| 00:00:01 |    943 |00:00:00.01 |       3 |       |       |          |
|   6 |     INDEX FAST FULL SCAN| PK_STAFF_DICT                |      1 |   3530 | 17650 |     3   (0)| 00:00:01 |   3544 |00:00:00.01 |      14 |       |       |          |
-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Query Block Name / Object Alias (identified by operation id):
-------------------------------------------------------------
   1 - SEL$C772B8D1
   2 - SEL$C772B8D1 / DEPT_DICT@SEL$1
   3 - SEL$683B0107 / VW_SQ_1@SEL$7511BFD2
   4 - SEL$683B0107
   5 - SEL$683B0107 / STAFF_VS_GROUP@SEL$2
   6 - SEL$683B0107 / STAFF_DICT@SEL$2
Predicate Information (identified by operation id):
---------------------------------------------------
   1 - access("GROUP_CODE"="DEPT_DICT"."DEPT_CODE")
   4 - access("STAFF_DICT"."EMP_NO"="STAFF_VS_GROUP"."EMP_NO")
   5 - access("STAFF_VS_GROUP"."GROUP_CLASS"='门诊医生')

--//逻辑读24.

时间： 2024-07-30 10:49:57

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