Statistics gathering and SQL Tuning Advisor
Posted feiyun8616的作坊 (半个程序员and dba)
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1. https://www.pythian.com/blog/statistics-gathering-and-sql-tuning-advisor/
Our monitoring software found a long running job on one of our client’s databases. The job was an Oracle’s auto task running statistics gathering for more than 3 hours. I was curious to know why it took so long and used a query to ASH to find out the most common SQL during the job run based on the module name. Results were surprising to me: top SQL was coming with SQL Tuning Advisor comment.
Here is the SQL I used:
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SQL> select s.sql_id, t.sql_text, s.cnt 2 from 3 (select * 4 from 5 ( 6 select sql_id, count(*) cnt 7 from v$active_session_history 8 where action like ‘ORA$AT_OS_OPT_SY%‘ 9 group by sql_id 10 order by count(*) desc 11 ) 12 where rownum <= 5 13 ) s, 14 dba_hist_sqltext t 15 where s.sql_id = t.sql_id;SQL_ID SQL_TEXT CNT------------- -------------------------------------------------------------------------------- ----------020t65s3ah2pq select substrb(dump(val,16,0,32),1,120) ep, cnt from (select /*+ no_expand_table 781byug0cc5vn416 /* SQL Analyze(1) */ select /*+ full(t) no_parallel(t) no_parallel_index(t) 43bkvvr4azs1n6z /* SQL Analyze(1) */ select /*+ full(t) no_parallel(t) no_parallel_index(t) 2146sy4dfg3xbfn /* SQL Analyze(1) */ select /*+ full(t) no_parallel(t) no_parallel_index(t) 1559 |
So most queries are coming with “SQL Analyze” comment right in the beginning of SQL which is running from DBMS_STATS call, which is confusing. After some bug search I have found a MOS Doc ID 1480132.1 which includes a PL/SQL stack trace from a DBMS_STATS procedure call, and it is going up to DBMS_SQLTUNE_INTERNAL, which means DBMS_STATS has a call to the SQL Tuning package; very odd:
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SQL> select * from dba_dependencies where name = ‘DBMS_STATS_INTERNAL‘ and referenced_name = ‘DBMS_SQLTUNE_INTERNAL‘;OWNER NAME TYPE REFERENCED_OWNER REFERENCED_NAME------------------------------
------------------------------ ------------------
------------------------------ ----------------------------------REFERENCED_TYPE
REFERENCED_LINK_NAME
DEPE------------------
-------------------------------------------------------------------------------------------------------------------------------SYS DBMS_STATS_INTERNAL PACKAGE BODY SYS DBMS_SQLTUNE_INTERNALPACKAGE
HARD |
Turns out, this call has nothing to do with the SQL Tuning. It is just a call to a procedure in this package, which happen to look like an SQL from SQL Tuning Advisor. I have traced a GATHER_TABLE_STATS call in a test database first with SQL trace and then with DBMS_HPROF and here is how the call tree looks like:
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SELECT RPAD(‘ ‘, (level-1)*2, ‘ ‘) || fi.owner || ‘.‘ || fi.module AS name, fi.function, pci.subtree_elapsed_time, pci.function_elapsed_time, pci.callsFROM dbmshp_parent_child_info pci JOIN dbmshp_function_info fi ON pci.runid = fi.runid AND pci.childsymid = fi.symbolidWHERE pci.runid = 1CONNECT BY PRIOR childsymid = parentsymid START WITH pci.parentsymid = 27;NAME
FUNCTION SUBTREE_ELAPSED_TIME
FUNCTION_ELAPSED_TIME CALLS----------------------------------------
------------------------------ --------------------
--------------------- --------------------...SYS.DBMS_STATS_INTERNAL
GATHER_SQL_STATS 21131962
13023 1 SYS.DBMS_ADVISOR
__pkg_init 88
88 1 SYS.DBMS_SQLTUNE_INTERNAL
GATHER_SQL_STATS 21118776
9440 1 SYS.DBMS_SQLTUNE_INTERNAL
I_PROCESS_SQL 21107094
21104225 1 SYS.DBMS_LOB
GETLENGTH 37
37 1 SYS.DBMS_LOB
INSTR 42
42 1 SYS.DBMS_LOB
__pkg_init 15
15 1 SYS.DBMS_SQLTUNE_INTERNAL
I_VALIDATE_PROCESS_ACTION 74
39 1 SYS.DBMS_UTILITY COMMA_TO_TABLE 35 35 1 SYS.DBMS_SQLTUNE_UTIL0
SQLTEXT_TO_SIGNATURE 532
532 1 SYS.DBMS_SQLTUNE_UTIL0
SQLTEXT_TO_SQLID 351
351 1 SYS.XMLTYPE
XMLTYPE 1818
1818 1 SYS.DBMS_SQLTUNE_UTIL0
SQLTEXT_TO_SQLID 528
528 1 SYS.DBMS_UTILITY
COMMA_TO_TABLE 88
88 1 SYS.DBMS_UTILITY
__pkg_init 10
10 1 SYS.SQLSET_ROW
SQLSET_ROW 33
33 1 SYS.XMLTYPE
XMLTYPE 1583
1583 1 SYS.DBMS_STATS_INTERNAL
DUMP_PQ_SESSTAT 73
73 1 SYS.DBMS_STATS_INTERNAL
DUMP_QUERY 2
2 1... |
So there is a procedure DBMS_SQLTUNE_INTERNAL.GATHER_SQL_STATS which is being called by DBMS_STATS_INTERNAL, and this procedure actually runs a SQL like this:
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/* SQL Analyze(0) */ select /*+
full(t) no_parallel(t) no_parallel_index(t) dbms_stats
cursor_sharing_exact use_weak_name_resl dynamic_sampling(0)
no_monitoring no_substrb_pad */to_char(count("ID")),to_char(substrb(dump(min("ID"),16,0,32),1,120)),to_char(substrb(dump(max("ID"),16,0,32),1,120)),to_char(count("X")),to_char(substrb(dump(min("X"),16,0,32),1,120)),to_char(substrb(dump(max("X"),16,0,32),1,120)),to_char(count("Y")),to_char(substrb(dump(min("Y"),16,0,32),1,120)),to_char(substrb(dump(max("Y"),16,0,32),1,120)),to_char(count("PAD")),to_char(substrb(dump(min("PAD"),16,0,32),1,120)),to_char(substrb(dump(max("PAD"),16,0,32),1,120)) from "TIM"."T1" t /* NDV,NIL,NIL,NDV,NIL,NIL,NDV,NIL,NIL,NDV,NIL,NIL*/ |
Which is basically approximate NDV calculation. So, nothing to be afraid of, it’s just the way the code is organized: DBMS_STATS uses API of SQL Tuning framework when you are using DBMS_STATS.AUTO_SAMPLE_SIZE as the ESTIMATE_PERCENT (which is the default & recommended value in 11g+).
2.
http://blog.csdn.net/stevendbaguo/article/details/50856002
接到现场数据库维护厂商发出的警告，有一条 insert语句执行了几千秒。
开发排查，从select * from dba_source s where s.text like ‘%XXX%‘;查到是一个存储过程，于是找到存储过程，将其改名。
但问题没有解决，隔天又收到警告。
难道是存储过程改名有问题，我远程到现场看了下，并没有问题。再次查看数据库报告：
SQL Module 是 DBMS_SCHEDULER，确定无疑是Oracle JOB调用，奇怪的是SQL语句有 /* SQL Analyze(194, 1) */ 这样的提示。
如果想定位到这条SQL，最好是找到这条SQL历史执行的session,希望找到蛛丝马迹。
select * from dba_hist_active_sess_history s where s.sql_id=‘29yrhxqdk2d1q‘;
TOP_LEVEL_SQL_ID 为5zruc4v6y32f9：说明是sql_id为5zruc4v6y32f9的调用的这条sql
MODULE：DBMS_SCHEDULER
PLSQL_ENTRY_OBJECT_ID：9013
根据上面的信息再进行查询：
9013;--结果是owner=sys object_name=dbms_sqltune
5zruc4v6y32f9
DECLARE
job BINARY_INTEGER := :job;
next_date TIMESTAMP WITH TIME ZONE := :mydate;
broken BOOLEAN := FALSE;
job_name VARCHAR2(30) := :job_name;
job_subname VARCHAR2(30) := :job_subname;
job_owner VARCHAR2(30) := :job_owner;
job_start TIMESTAMP WITH TIME ZONE := :job_start;
job_scheduled_start TIMESTAMP WITH TIME ZONE := :job_scheduled_start;
window_start TIMESTAMP WITH TIME ZONE := :window_start;
window_end TIMESTAMP WITH TIME ZONE := :window_end;
chain_id VARCHAR2(14) := :chainid;
credential_owner varchar2(30) := :credown;
credential_name varchar2(30) := :crednam;
destination_owner varchar2(30) := :destown;
destination_name varchar2(30) := :destnam;
job_dest_id varchar2(14) := :jdestid;
log_id number := :log_id;
BEGIN
DECLARE
ename VARCHAR2(30);
BEGIN
ename := dbms_sqltune.execute_tuning_task(‘SYS_AUTO_SQL_TUNING_TASK‘);
END;
:mydate := next_date;
IF broken THEN
:b := 1;
ELSE
:b := 0;
END IF;
END;
这是数据库SQL优化的包，自己调用的，终于明白 /* SQL Analyze(194, 1) */的意思了，是标记这种优化包调用的。
3.
http://blog.itpub.net/23718752/viewspace-1252180/
在昨天晚上10点开始，数据库的性能开始下降，出现了一些j00开头的进程。
而且持续了比较长的时间，简单分析了一下，对应的进程执行的sql语句如下。
####### Process Information from OS level as below ########
oraccbs1 16184 1 23 22:00 ? 00:03:09 ora_j000_PETCUS1
oraccbs1 20829 12754 0 22:14 pts/12 00:00:00 ksh showpid.sh 16184
##############################################
SID SERIAL# USERNAME OSUSER
MACHINE PROCESS TERMINAL TYPE
LOGIN_TIME
---------- ---------- --------------- ---------------
-------------------- --------------- --------------- ----------
-------------------
1139 1071 SYS oraccbs1
xxxxxx 16184 UNKNOWN USER
2014-08-14 22:00:43
.
SQL_ID SQL_TEXT
------------------------------ ------------------------------------------------------------
6fwshkjydz9ph /* SQL Analyze(1) */ select /*+ full(t) no_parallel(t) n
o_parallel_index(t) dbms_stats cursor_sharing_exact use_weak
_name_resl dynamic_sampling(0) no_monitoring no_substrb_pad
*/to_char(count("PERIOD_KEY")),to_char(substrb(dump(min("PE
RIOD_KEY"),16,0,32),1,120)),to_char(substrb(dump(max("PERIOD
_KEY"),16,0,32),1,120)),to_char(count("PARTITION_ID")),to_ch
ar(substrb(dump(min("PARTITION_ID"),16,0,32),1,120)),to_char
(substrb(dump(max("PARTITION_ID"),16,0,32),1,120)),to_char(c
ount("DEBIT_ID")),to_char(substrb(dump(min("DEBIT_ID"),16,0,
32),1,120)),to_char(substrb(dump(max("DEBIT_ID"),16,0,32),1,
120)),to_char(count("SYS_CREATION_DATE")),to_char(substrb(du
mp(min("SYS_CREATION_DATE"),16,0,32),1,120)),to_char(substrb
(dump(max("SYS_CREATION_DATE"),16,0,32),1,120)),to_char(coun
t("SYS_UPDATE_DATE")),to_char(substrb(dump(min("SYS_UPDATE_D
ATE"),16,0,32),1,120)),to_char(substrb(dump(max("SYS_UPDATE_
DATE"),16,0,32),1,120)),to_char(count("OPERATOR_ID")),to_cha
r(substrb(dump(min("OPERATOR_ID"),16,0,3
PREV_SQL_ID SQL_TEXT
------------------------------ ------------------------------------------------------------
fhzj09a7fnrnb SELECT DBTIMEZONE, LENGTH(DBTIMEZONE) FROM SYS.DUAL
看起来是在做一些后台的维护工作。在11g中引入了几个schedule job，简单查询，结果如下。可以看到在每天都设置了对应的window。
在10点开始做一些工作。以下是禁用以后的状态。
SQL> execute DBMS_AUTO_TASK_ADMIN.DISABLE;
PL/SQL procedure successfully completed.
SQL> select * from DBA_AUTOTASK_WINDOW_CLIENTS;
WINDOW_NAME
WINDOW_NEXT_TIME
WINDO AUTOTASK OPTIMIZE SEGMENT_ SQL_TUNE HEALTH_M
------------------------------
---------------------------------------------------------------------------
----- -------- -------- -------- -------- --------
MONDAY_WINDOW 18-AUG-14 10.00.00.000000 PM
ASIA/PHNOM_PENH FALSE DISABLED ENABLED
ENABLED ENABLED DISABLED
TUESDAY_WINDOW 19-AUG-14 10.00.00.000000 PM
ASIA/PHNOM_PENH FALSE DISABLED ENABLED
ENABLED ENABLED DISABLED
WEDNESDAY_WINDOW 20-AUG-14 10.00.00.000000 PM
ASIA/PHNOM_PENH FALSE DISABLED ENABLED
ENABLED ENABLED DISABLED
THURSDAY_WINDOW 14-AUG-14 10.00.00.000000 PM
ASIA/PHNOM_PENH TRUE DISABLED ENABLED
ENABLED ENABLED DISABLED
FRIDAY_WINDOW 15-AUG-14 10.00.00.000000 PM
ASIA/PHNOM_PENH FALSE DISABLED ENABLED
ENABLED ENABLED DISABLED
SATURDAY_WINDOW 16-AUG-14 06.00.00.000000 AM
ASIA/PHNOM_PENH FALSE DISABLED ENABLED
ENABLED ENABLED DISABLED
SUNDAY_WINDOW 17-AUG-14 06.00.00.000000 AM
ASIA/PHNOM_PENH FALSE DISABLED ENABLED
ENABLED ENABLED DISABLED
7 rows selected.
其实3个主要的后台job可以选择关掉。
SQL> select client_name,status from DBA_AUTOTASK_CLIENT;
CLIENT_NAME STATUS
---------------------------------------------------------------- --------
auto optimizer stats collection ENABLED
auto space advisor ENABLED
sql tuning advisor ENABLED
使用如下的pl/sql来禁用。
begin
DBMS_AUTO_TASK_ADMIN.DISABLE(client_name => ‘auto optimizer stats collection‘,
operation => NULL,
window_name => NULL);
end;
/
begin
DBMS_AUTO_TASK_ADMIN.DISABLE(client_name => ‘auto space advisor‘,
operation => NULL,
window_name => NULL);
end;
/
begin
DBMS_AUTO_TASK_ADMIN.DISABLE(client_name => ‘sql tuning advisor‘,
operation => NULL,
window_name => NULL);
end;
/
禁用以后，状态如下：
SQL> select client_name,status from DBA_AUTOTASK_CLIENT;
CLIENT_NAME STATUS
---------------------------------------------------------------- --------
auto optimizer stats collection DISABLED
auto space advisor DISABLED
sql tuning advisor DISABLED
但是不会当时生效，需要过一段时间，所以需要提前禁用。
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