[案例] 字元型欄位統計資訊只對前32位進行統計
系統一個SQL緩慢，從執行計劃來看，SQL走了全表掃描
但是SQL很簡單，就是FLOW_INSTANCE_ID等於1個值，就取一條資料出來。並且該列上是存在索引的
統計資訊也是很新的，從統計資訊看，SQL不可能去選擇全表掃描
****************************************************************************************
CURSOR
****************************************************************************************
SQL_ID 93vkutmkygmwg, child number 4
-------------------------------------
select flowinstan0_.FLOW_ID as FLOW_ID, flowinstan0_.FLOW_INSTANCE_ID as
FLOW_INS2_, flowinstan0_.STS as STS, flowinstan0_.STS_DATE as STS_DATE,
flowinstan0_.TEMPLATE_FLAG as TEMPLATE5_, flowinstan0_.APPL_DATE as
APPL_DATE, flowinstan0_.COMPL_DATE as COMPL_DATE, flowinstan0_.USE_FLAG as
USE_FLAG, flowinstan0_.ORDER_ID as ORDER_ID from FLOW_INSTANCE
flowinstan0_ where (flowinstan0_.FLOW_INSTANCE_ID=:1 )
Plan hash value: 705113994
-----------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
-----------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | | | 16505 (100)| |
|* 1 | TABLE ACCESS FULL| FLOW_INSTANCE | 621K| 52M| 16505 (1)| 00:03:19 |
-----------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
1 - filter("FLOWINSTAN0_"."FLOW_INSTANCE_ID"=:1)
23 rows selected.
****************************************************************************************
SQL STATS
****************************************************************************************
CPU ELAPSED DISK BUFFER ROWS PARSE
TIME TIME READS GETS PROCESSED FETCHES CALLS SORTS EXEC
------------ ------------ ------------ ------------ ------------ ------------ -------- -------- ------------
############ ############ 323,771,818 ############ 819,410 825,145 825,637 0 825,639
CPU ELA DISK GET ROWS ROWS
PRE EXEC PRE EXEC PRE EXEC PRE EXEC PRE EXEC PRE FETCHES EXEC
------------ ------------ ------------ ------------ ------------ ------------ ------------
503,471 2,112,582 392 1,802 1 1 825,639
CPU ELA DISK GET ROWS ROWS PLAN CHILD USER
PRE EXEC PRE EXEC PRE EXEC PRE EXEC PRE EXEC PRE FETCHES EXEC HASH VALUE NUMBER NAME
------------ ------------ ------------ ------------ ------------ ------------ ------------ ------------- ------- ----------
457,500 3,912,946 995 75,292 1 1 120 705113994 4 SP
****************************************************************************************
TABLES
****************************************************************************************
TABLE BUFFER NUM EMPTY AVG AVG LAST
OWNER NAME LOG POOL DEGREE PART ROWS BLOCKS BLOCKS SPACE ROW_LEN ANALYZED
---------- --------------- --- ------- ------ ---- ------------ ------------ ------------ ------------ ------------ --------
SP FLOW_INSTANCE YES DEFAULT 1 NO 2,869,680 85,322 22 1,623 97 20120927
****************************************************************************************
INDEX INFO
****************************************************************************************
TABLE TABLE Index COLUMN Col
OWNER NAME Name Unique NAME Pos DESC
---------- --------------- ------------------------------ --------- --------------- ---- ----
SP FLOW_INSTANCE IDX_FLOW_INSTANCE_1 NONUNIQUE ORDER_ID 1 ASC
IDX_FLOW_INSTANCE_FII NONUNIQUE FLOW_INSTANCE_I 1 ASC
D
PK_FLOW_INSTANCE UNIQUE FLOW_ID 1 ASC
FLOW_INSTANCE_I 2 ASC
D
****************************************************************************************
LITERAL SQL
****************************************************************************************
DECLARE
*
ERROR at line 1:
ORA-01403: no data found
ORA-06512: at line 33
****************************************************************************************
SQL WAIT HIST
****************************************************************************************
WAIT
PROGRAM EVENT TOTAL CLASS
------------------------------ ---------------------------------------- -------- ---------------
CPU 55,969 CPU
read by other session 19,353 User_IO
latch: cache buffers chains 4,280 Concurrency
db file sequential read 3,865 User_IO
db file scattered read 2,412 User_IO
latch free 1,034 Other
wait list latch free 9 Other
latch: shared pool 1 Concurrency
library cache lock 1 Concurrency
latch: In memory undo latch 1 Concurrency
10 rows selected.
****************************************************************************************
TABLE COLUMNS
****************************************************************************************
TABLE COLUMN DATA NUM NUM AVG LAST
OWNER NAME NAME TYPE NL HIST DENSITY NULLS BUCKETS COL LEN ANALYZED
----- --------------- --------------- --------------- -- ----- ------------ ------------ ------------ ------------ --------
SP FLOW_INSTANCE FLOW_ID VARCHAR2 N FREQU 0 0 24 5 20120927
FLOW_INSTANCE_I VARCHAR2 N HEIGH 0 0 254 39 20120927
D
ORDER_ID VARCHAR2 N NONE 0 0 1 16 20120927
STS CHAR Y FREQU 0 0 4 2 20120927
STS_DATE DATE Y HEIGH 0 120 254 8 20120927
TEMPLATE_FLAG CHAR Y NONE 0 2,869,680 0 1 20120927
APPL_DATE DATE Y HEIGH 0 130 254 8 20120927
COMPL_DATE DATE Y NONE 0 768,830 1 7 20120927
USE_FLAG CHAR Y FREQU 0 0 2 2 20120927
INSERT_MOMENT TIMESTAMP(6) N NONE 0 0 1 11 20120927
10 rows selected.
****************************************************************************************
INDEX STATS
****************************************************************************************
B Average Average
Index Tree Leaf Distinct NUM Leaf Blocks Data Blocks Cluster LAST
OWNER Name LOG STATUS Level Blks Keys ROWS Per Key Per Key Factor ANALYZED
---------- --------------- --- ------ ----- -------- ------------ ------------ ----------- ----------- ------------ --------
SP IDX_FLOW_INSTAN YES VALID 3 59,560 91,141 2,745,090 1 28 2,597,090 20120927
CE_FII
IDX_FLOW_INSTAN YES VALID 2 30,800 1,819,234 2,872,140 1 1 2,698,230 20120927
CE_1
PK_FLOW_INSTANC YES VALID 3 61,340 2,895,090 2,895,090 1 1 2,738,820 20120927
E
先嚐試下sql advisor，結果無任何建議
DBMS_SQLTUNE.REPORT_TUNING_TASK(:MY_TASK_NAME)
----------------------------------------------------------------------------------------------------
GENERAL INFORMATION SECTION
-------------------------------------------------------------------------------
Tuning Task Name : sqltuning_zq_20120927171516
Tuning Task Owner : SYS
Scope : COMPREHENSIVE
Time Limit(seconds): 60
Completion Status : COMPLETED
Started at : 09/27/2012 17:15:18
Completed at : 09/27/2012 17:15:21
-------------------------------------------------------------------------------
Schema Name: SP
SQL ID : 93vkutmkygmwg
SQL Text : select flowinstan0_.FLOW_ID as FLOW_ID,
flowinstan0_.FLOW_INSTANCE_ID as FLOW_INS2_, flowinstan0_.STS as
STS, flowinstan0_.STS_DATE as STS_DATE,
flowinstan0_.TEMPLATE_FLAG as TEMPLATE5_, flowinstan0_.APPL_DATE
as APPL_DATE, flowinstan0_.COMPL_DATE as COMPL_DATE,
flowinstan0_.USE_FLAG as USE_FLAG, flowinstan0_.ORDER_ID as
ORDER_ID from FLOW_INSTANCE flowinstan0_ where
(flowinstan0_.FLOW_INSTANCE_ID=:1 )
-------------------------------------------------------------------------------
There are no recommendations to improve the statement.
-------------------------------------------------------------------------------
注意到在FLOW_INSTANCE_ID上，是收集了HEIGH的直方圖的。
由於該SQL在已經沒有變數的值存放，於是找開發人員獲得FLOW_INSTANCE_ID的值Direct_CDMA_PR_iSPP_IVPN_SICHUAN-201209229512416
select flowinstan0_.FLOW_ID as FLOW_ID, flowinstan0_.FLOW_INSTANCE_ID as FLOW_INS2_, flowinstan0_.STS as STS,
flowinstan0_.STS_DATE as STS_DATE, flowinstan0_.TEMPLATE_FLAG as TEMPLATE5_, flowinstan0_.APPL_DATE as APPL_DATE,
flowinstan0_.COMPL_DATE as COMPL_DATE, flowinstan0_.USE_FLAG as USE_FLAG, flowinstan0_.ORDER_ID as ORDER_ID from FLOW_INSTANCE
flowinstan0_ where (flowinstan0_.FLOW_INSTANCE_ID='Direct_CDMA_PR_iSPP_IVPN_SICHUAN-201209229512416' )
這個引數太長，一般對於字元型，ORACLE只在欄位統計資訊中保留前32位。這個值前32位幾乎一模一樣。
也就是說，直方圖是造成該故障的主要原因。
SQL> exec dbms_stats.gather_table_stats('SP','FLOW_INSTANCE',NO_INVALIDATE=>false,DEGREE=>2,ESTIMATE_PERCENT=>10,method_opt=>'for all indexed columns size 1')
PL/SQL procedure successfully completed.
將直方圖刪除後，SQL正常.
為安全起見，為SQL繫結profile
SQL> @staexchange.sql
Enter value for sql_id1(used to generate sql_text): 93vkutmkygmwg
Enter value for child_no1 (used to generate sql_text) (0): 3
Enter value for sql_id2(used to generate sql_hints): 93vkutmkygmwg
Enter value for child_no2(used to generate sql_hints) (0): 3
Enter value for profile_name (PROF_sqlid_planhash):
Enter value for category (DEFAULT):
Enter value for force_matching (FALSE): true
SQL Profile PROF_93vkutmkygmwg_4040583430 created.
檢視正常的執行計劃
SQL_ID 93vkutmkygmwg, child number 0
-------------------------------------
select flowinstan0_.FLOW_ID as FLOW_ID, flowinstan0_.FLOW_INSTANCE_ID as FLOW_INS2_,
flowinstan0_.STS as STS, flowinstan0_.STS_DATE as STS_DATE, flowinstan0_.TEMPLATE_FLAG as
TEMPLATE5_, flowinstan0_.APPL_DATE as APPL_DATE, flowinstan0_.COMPL_DATE as COMPL_DATE,
flowinstan0_.USE_FLAG as USE_FLAG, flowinstan0_.ORDER_ID as ORDER_ID from FLOW_INSTANCE
flowinstan0_ where (flowinstan0_.FLOW_INSTANCE_ID=:1 )
Plan hash value: 4040583430
-----------------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
-----------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | | | 5 (100)| |
| 1 | TABLE ACCESS BY INDEX ROWID| FLOW_INSTANCE | 1 | 88 | 5 (0)| 00:00:01 |
|* 2 | INDEX RANGE SCAN | IDX_FLOW_INSTANCE_FII | 1 | | 4 (0)| 00:00:01 |
-----------------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
2 - access("FLOWINSTAN0_"."FLOW_INSTANCE_ID"=:1)
Note
-----
- SQL profile "PROF_93vkutmkygmwg_4040583430" used for this statement
27 rows selected.
但是SQL很簡單，就是FLOW_INSTANCE_ID等於1個值，就取一條資料出來。並且該列上是存在索引的
統計資訊也是很新的，從統計資訊看，SQL不可能去選擇全表掃描
****************************************************************************************
CURSOR
****************************************************************************************
SQL_ID 93vkutmkygmwg, child number 4
-------------------------------------
select flowinstan0_.FLOW_ID as FLOW_ID, flowinstan0_.FLOW_INSTANCE_ID as
FLOW_INS2_, flowinstan0_.STS as STS, flowinstan0_.STS_DATE as STS_DATE,
flowinstan0_.TEMPLATE_FLAG as TEMPLATE5_, flowinstan0_.APPL_DATE as
APPL_DATE, flowinstan0_.COMPL_DATE as COMPL_DATE, flowinstan0_.USE_FLAG as
USE_FLAG, flowinstan0_.ORDER_ID as ORDER_ID from FLOW_INSTANCE
flowinstan0_ where (flowinstan0_.FLOW_INSTANCE_ID=:1 )
Plan hash value: 705113994
-----------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
-----------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | | | 16505 (100)| |
|* 1 | TABLE ACCESS FULL| FLOW_INSTANCE | 621K| 52M| 16505 (1)| 00:03:19 |
-----------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
1 - filter("FLOWINSTAN0_"."FLOW_INSTANCE_ID"=:1)
23 rows selected.
****************************************************************************************
SQL STATS
****************************************************************************************
CPU ELAPSED DISK BUFFER ROWS PARSE
TIME TIME READS GETS PROCESSED FETCHES CALLS SORTS EXEC
------------ ------------ ------------ ------------ ------------ ------------ -------- -------- ------------
############ ############ 323,771,818 ############ 819,410 825,145 825,637 0 825,639
CPU ELA DISK GET ROWS ROWS
PRE EXEC PRE EXEC PRE EXEC PRE EXEC PRE EXEC PRE FETCHES EXEC
------------ ------------ ------------ ------------ ------------ ------------ ------------
503,471 2,112,582 392 1,802 1 1 825,639
CPU ELA DISK GET ROWS ROWS PLAN CHILD USER
PRE EXEC PRE EXEC PRE EXEC PRE EXEC PRE EXEC PRE FETCHES EXEC HASH VALUE NUMBER NAME
------------ ------------ ------------ ------------ ------------ ------------ ------------ ------------- ------- ----------
457,500 3,912,946 995 75,292 1 1 120 705113994 4 SP
****************************************************************************************
TABLES
****************************************************************************************
TABLE BUFFER NUM EMPTY AVG AVG LAST
OWNER NAME LOG POOL DEGREE PART ROWS BLOCKS BLOCKS SPACE ROW_LEN ANALYZED
---------- --------------- --- ------- ------ ---- ------------ ------------ ------------ ------------ ------------ --------
SP FLOW_INSTANCE YES DEFAULT 1 NO 2,869,680 85,322 22 1,623 97 20120927
****************************************************************************************
INDEX INFO
****************************************************************************************
TABLE TABLE Index COLUMN Col
OWNER NAME Name Unique NAME Pos DESC
---------- --------------- ------------------------------ --------- --------------- ---- ----
SP FLOW_INSTANCE IDX_FLOW_INSTANCE_1 NONUNIQUE ORDER_ID 1 ASC
IDX_FLOW_INSTANCE_FII NONUNIQUE FLOW_INSTANCE_I 1 ASC
D
PK_FLOW_INSTANCE UNIQUE FLOW_ID 1 ASC
FLOW_INSTANCE_I 2 ASC
D
****************************************************************************************
LITERAL SQL
****************************************************************************************
DECLARE
*
ERROR at line 1:
ORA-01403: no data found
ORA-06512: at line 33
****************************************************************************************
SQL WAIT HIST
****************************************************************************************
WAIT
PROGRAM EVENT TOTAL CLASS
------------------------------ ---------------------------------------- -------- ---------------
CPU 55,969 CPU
read by other session 19,353 User_IO
latch: cache buffers chains 4,280 Concurrency
db file sequential read 3,865 User_IO
db file scattered read 2,412 User_IO
latch free 1,034 Other
wait list latch free 9 Other
latch: shared pool 1 Concurrency
library cache lock 1 Concurrency
latch: In memory undo latch 1 Concurrency
10 rows selected.
****************************************************************************************
TABLE COLUMNS
****************************************************************************************
TABLE COLUMN DATA NUM NUM AVG LAST
OWNER NAME NAME TYPE NL HIST DENSITY NULLS BUCKETS COL LEN ANALYZED
----- --------------- --------------- --------------- -- ----- ------------ ------------ ------------ ------------ --------
SP FLOW_INSTANCE FLOW_ID VARCHAR2 N FREQU 0 0 24 5 20120927
FLOW_INSTANCE_I VARCHAR2 N HEIGH 0 0 254 39 20120927
D
ORDER_ID VARCHAR2 N NONE 0 0 1 16 20120927
STS CHAR Y FREQU 0 0 4 2 20120927
STS_DATE DATE Y HEIGH 0 120 254 8 20120927
TEMPLATE_FLAG CHAR Y NONE 0 2,869,680 0 1 20120927
APPL_DATE DATE Y HEIGH 0 130 254 8 20120927
COMPL_DATE DATE Y NONE 0 768,830 1 7 20120927
USE_FLAG CHAR Y FREQU 0 0 2 2 20120927
INSERT_MOMENT TIMESTAMP(6) N NONE 0 0 1 11 20120927
10 rows selected.
****************************************************************************************
INDEX STATS
****************************************************************************************
B Average Average
Index Tree Leaf Distinct NUM Leaf Blocks Data Blocks Cluster LAST
OWNER Name LOG STATUS Level Blks Keys ROWS Per Key Per Key Factor ANALYZED
---------- --------------- --- ------ ----- -------- ------------ ------------ ----------- ----------- ------------ --------
SP IDX_FLOW_INSTAN YES VALID 3 59,560 91,141 2,745,090 1 28 2,597,090 20120927
CE_FII
IDX_FLOW_INSTAN YES VALID 2 30,800 1,819,234 2,872,140 1 1 2,698,230 20120927
CE_1
PK_FLOW_INSTANC YES VALID 3 61,340 2,895,090 2,895,090 1 1 2,738,820 20120927
E
先嚐試下sql advisor，結果無任何建議
DBMS_SQLTUNE.REPORT_TUNING_TASK(:MY_TASK_NAME)
----------------------------------------------------------------------------------------------------
GENERAL INFORMATION SECTION
-------------------------------------------------------------------------------
Tuning Task Name : sqltuning_zq_20120927171516
Tuning Task Owner : SYS
Scope : COMPREHENSIVE
Time Limit(seconds): 60
Completion Status : COMPLETED
Started at : 09/27/2012 17:15:18
Completed at : 09/27/2012 17:15:21
-------------------------------------------------------------------------------
Schema Name: SP
SQL ID : 93vkutmkygmwg
SQL Text : select flowinstan0_.FLOW_ID as FLOW_ID,
flowinstan0_.FLOW_INSTANCE_ID as FLOW_INS2_, flowinstan0_.STS as
STS, flowinstan0_.STS_DATE as STS_DATE,
flowinstan0_.TEMPLATE_FLAG as TEMPLATE5_, flowinstan0_.APPL_DATE
as APPL_DATE, flowinstan0_.COMPL_DATE as COMPL_DATE,
flowinstan0_.USE_FLAG as USE_FLAG, flowinstan0_.ORDER_ID as
ORDER_ID from FLOW_INSTANCE flowinstan0_ where
(flowinstan0_.FLOW_INSTANCE_ID=:1 )
-------------------------------------------------------------------------------
There are no recommendations to improve the statement.
-------------------------------------------------------------------------------
注意到在FLOW_INSTANCE_ID上，是收集了HEIGH的直方圖的。
由於該SQL在已經沒有變數的值存放，於是找開發人員獲得FLOW_INSTANCE_ID的值Direct_CDMA_PR_iSPP_IVPN_SICHUAN-201209229512416
select flowinstan0_.FLOW_ID as FLOW_ID, flowinstan0_.FLOW_INSTANCE_ID as FLOW_INS2_, flowinstan0_.STS as STS,
flowinstan0_.STS_DATE as STS_DATE, flowinstan0_.TEMPLATE_FLAG as TEMPLATE5_, flowinstan0_.APPL_DATE as APPL_DATE,
flowinstan0_.COMPL_DATE as COMPL_DATE, flowinstan0_.USE_FLAG as USE_FLAG, flowinstan0_.ORDER_ID as ORDER_ID from FLOW_INSTANCE
flowinstan0_ where (flowinstan0_.FLOW_INSTANCE_ID='Direct_CDMA_PR_iSPP_IVPN_SICHUAN-201209229512416' )
這個引數太長，一般對於字元型，ORACLE只在欄位統計資訊中保留前32位。這個值前32位幾乎一模一樣。
也就是說，直方圖是造成該故障的主要原因。
SQL> exec dbms_stats.gather_table_stats('SP','FLOW_INSTANCE',NO_INVALIDATE=>false,DEGREE=>2,ESTIMATE_PERCENT=>10,method_opt=>'for all indexed columns size 1')
PL/SQL procedure successfully completed.
將直方圖刪除後，SQL正常.
為安全起見，為SQL繫結profile
SQL> @staexchange.sql
Enter value for sql_id1(used to generate sql_text): 93vkutmkygmwg
Enter value for child_no1 (used to generate sql_text) (0): 3
Enter value for sql_id2(used to generate sql_hints): 93vkutmkygmwg
Enter value for child_no2(used to generate sql_hints) (0): 3
Enter value for profile_name (PROF_sqlid_planhash):
Enter value for category (DEFAULT):
Enter value for force_matching (FALSE): true
SQL Profile PROF_93vkutmkygmwg_4040583430 created.
檢視正常的執行計劃
SQL_ID 93vkutmkygmwg, child number 0
-------------------------------------
select flowinstan0_.FLOW_ID as FLOW_ID, flowinstan0_.FLOW_INSTANCE_ID as FLOW_INS2_,
flowinstan0_.STS as STS, flowinstan0_.STS_DATE as STS_DATE, flowinstan0_.TEMPLATE_FLAG as
TEMPLATE5_, flowinstan0_.APPL_DATE as APPL_DATE, flowinstan0_.COMPL_DATE as COMPL_DATE,
flowinstan0_.USE_FLAG as USE_FLAG, flowinstan0_.ORDER_ID as ORDER_ID from FLOW_INSTANCE
flowinstan0_ where (flowinstan0_.FLOW_INSTANCE_ID=:1 )
Plan hash value: 4040583430
-----------------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
-----------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | | | 5 (100)| |
| 1 | TABLE ACCESS BY INDEX ROWID| FLOW_INSTANCE | 1 | 88 | 5 (0)| 00:00:01 |
|* 2 | INDEX RANGE SCAN | IDX_FLOW_INSTANCE_FII | 1 | | 4 (0)| 00:00:01 |
-----------------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
2 - access("FLOWINSTAN0_"."FLOW_INSTANCE_ID"=:1)
Note
-----
- SQL profile "PROF_93vkutmkygmwg_4040583430" used for this statement
27 rows selected.
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