Statistics gathering and SQL Tuning Advisor

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:

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 781

byug0cc5vn416 /* SQL Analyze(1) */ select /*+ full(t) no_parallel(t) no_parallel_index(t) 43

bkvvr4azs1n6z /* SQL Analyze(1) */ select /*+ full(t) no_parallel(t) no_parallel_index(t) 21

46sy4dfg3xbfn /* 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:

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_INTERNAL

PACKAGE                                                                                                                                    

 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:

SELECT RPAD(' ', (level-1)*2, ' ') || fi.owner || '.' || fi.module AS name,

fi.function,

pci.subtree_elapsed_time,

pci.function_elapsed_time,

pci.calls

FROM dbmshp_parent_child_info pci

JOIN dbmshp_function_info fi ON pci.runid = fi.runid AND pci.childsymid = fi.symbolid

WHERE pci.runid = 1

CONNECT 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:

/* 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+).

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。

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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