oracle 定位热块和热链的方法

定位热链的方法

declare
        v_num number;
begin
        for i in
1..1000000
        loop
                select sal into
v_num
                from emp
                where
ename='SMITH';
        end loop;
end;
/

declare
        v_num number;
begin
        for i in
1..1000000
        loop
                select sal into
v_num
                from emp
                where
ename='KING';
        end loop;
end;
/

declare
        v_num number;
begin
        for i in
1..1000000
        loop
                select sal into
v_num
                from emp
                where
ename='SCOTT';
        end loop;
end;
/

一.获取当前系统等待事件
select event, count(*) from v$session
where wait_class
<> 'Idle' group by event order by 2;

EVENT           
COUNT(*)
----------------------------------------------------------
----------
SQL*Net message to client         1
latch: cache buffers
chains         1

SYS@ora10g>

二.获取哪些活跃会话正在处于latch: cache buffers chains
select
sid,username,event,p1raw,sql_id,logon_time,last_call_et
from v$session where
event='latch: cache buffers chains' and status='ACTIVE'
SYS@ora10g> /

SID USERNAME      EVENT       P1RAW      SQL_ID  LOGON_TIM
LAST_CALL_ET
----------- ---------------- ------------------------------
------------------------------ ------------- --------- ------------
 138
SCOTT      latch: cache buffers chains    0000000082FED878     766dr19szth9c
07-OCT-14      18
 140 SCOTT      latch: cache buffers chains   
0000000082E3FCC0     5mmqfh10738vp 07-OCT-14      15

SYS@ora10g>

三.确认等待的P1RAW是否出现很多是相同的.
SYS@ora10g>
l
  1  select sid,p1raw,p2,p3,seconds_in_wait,wait_time,state from
v$session_wait
  2* where event='latch: cache buffers chains' order by
3,2
SYS@ora10g> /

SID P1RAW       P2  P3 SECONDS_IN_WAIT  WAIT_TIME STATE
-----------
---------------- ---------- ---------- --------------- ----------
-------------------
 140 0000000082E3FCC0     122   1  15    10 WAITED KNOWN
TIME
 138 0000000082E3FCC0     122   0   3    -1 WAITED SHORT TIME

SYS@ora10g>

四.找出这个latch管理的对象.
 关注TCH值
SYS@ora10g> undefine latch_addr
SYS@ora10g> l
    select
a.hladdr,a.file#,a.dbablk,a.tch,a.obj,b.object_name from x$bh a, dba_objects
b
    where (a.obj = b.object_id or a.obj = b.data_object_id) and a.hladdr =
'&&latch_addr'
    union select hladdr,file#,dbablk,tch,obj,null from
x$bh
   where obj in (select obj from x$bh where hladdr = '&latch_addr'

   minus select object_id from dba_objects
   minus select
data_object_id from dba_objects) and hladdr = '&latch_addr' order by 4
SYS@ora10g> /
Enter value for latch_addr:
0000000082E3FCC0

HLADDR        FILE# DBABLK       TCH  OBJ OBJECT_NAME
----------------
---------- ---------- ---------- ----------
------------------------------
0000000082E3FCC0   1  55349  0   92
DEPENDENCY$
0000000082E3FCC0   2   1662  1 4294967295
0000000082E3FCC0  
3    963  1 3709 WRI$_ADV_RATIONALE_PK
0000000082E3FCC0   3  
4835  1 9246
0000000082E3FCC0   3   5068  1      51296
ORDER_ITEMS
0000000082E3FCC0   3   5068  1      51296
WRH$_PARAMETER
0000000082E3FCC0   4  17383  1      52516
O1
0000000082E3FCC0   4  39306  1      52516 O1
0000000082E3FCC0   4 
60530  1      52516 O1
0000000082E3FCC0   4  60763  1      52516
O1
0000000082E3FCC0   4  60996  1      52516 O1
0000000082E3FCC0   4 
61229  1      52516 O1
0000000082E3FCC0   4  64868  1      52516
O1
0000000082E3FCC0   4  65101  1      52516 O1
0000000082E3FCC0   4 
65334  1      52516 O1
0000000082E3FCC0   4  65567  1      52516
O1
0000000082E3FCC0   4  69206  1      52516 O1
0000000082E3FCC0   4 
69439  1      52516 O1
0000000082E3FCC0   4  69672  1      52516
O1
0000000082E3FCC0   4  69905  1      52516 O1
0000000082E3FCC0   4 
70138  1      52516 O1
0000000082E3FCC0   3  23119        39      49873
SYS_IOT_OVER_49872
0000000082E3FCC0   4     31       411      51151 EMP

23 rows selected.

SYS@ora10g>

五.根据sql_id获取到相应SQL.结合SQL中的对象.结合上面的TCH值进一步判断热块.
SYS@ora10g> select executions,sql_text from
v$sqlarea where sql_id in ('766dr19szth9c','5mmqfh10738vp');

EXECUTIONS SQL_TEXT
----------
------------------------------------------------------------
   7000000
SELECT SAL FROM EMP WHERE ENAME='KING'
  45374216 SELECT SAL FROM EMP WHERE
ENAME='SCOTT'

SYS@ora10g>

六.复杂SQL,太多表关联,要依据执行计划来判断.

定位热块的方法

 

latch: buffer busy waits    等待事件
 原因:
  热块 修改导致

declare
        v_num number;
begin
   for i in 1..1000000
 
 loop
    select sal into v_num
    from emp
    where
ename='SMITH';
      update emp set sal=sal+0
     where
ename='SMITH';
     commit;
   end loop;
end;
/

declare
        v_num number;
begin
   for i in 1..1000000
 
 loop
    select sal into v_num
    from emp
    where
ename='KING';
      update emp set sal=sal+0
     where
ename='KING';
     commit;
   end loop;
end;
/

declare
        v_num number;
begin
   for i in 1..1000000
 
 loop
    select sal into v_num
    from emp
    where
ename='SCOTT';
      update emp set sal=sal+0
     where
ename='SCOTT';
     commit;
   end loop;
end;
/

SYS@ora10g> select event, count(*)
from v$session where wait_class <> 'Idle' group by event order by 2;
SYS@ora10g> /

EVENT           
COUNT(*)
----------------------------------------------------------
----------
log file switch (checkpoint incomplete)        1
SQL*Net
message to client         1
buffer busy waits          2

SYS@ora10g>

SYS@ora10g> select
sid,username,event,p1,p2,p3,sql_id,logon_time,last_call_et
   from v$session
where event='buffer busy waits' and status='ACTIVE'

SYS@ora10g> /

SID USERNAME      EVENT        P1        P2   P3 SQL_ID    LOGON_TIM
LAST_CALL_ET
----------- ---------------- ------------------------------
---------- ---------- ---------- ------------- --------- ------------
 138
SCOTT      buffer busy waits        4        32    1 dh3kc1jqtnxw5
07-OCT-14       249
 140 SCOTT      buffer busy waits        4        32    1
71ssxfx45kyrh 07-OCT-14       246
 158 SCOTT      buffer busy waits       
4        32    1 5vcss49awm6fn 07-OCT-14       252

SYS@ora10g>

SELECT  owner , segment_name , segment_type
    FROM 
dba_extents
    WHERE  file_id = &FileNumber
   AND  &BlockNumber
BETWEEN block_id AND block_id + blocks -1
SYS@ora10g> /
Enter value for filenumber:
4
old   3: WHERE file_id = &FileNumber
new   3: WHERE file_id =
4
Enter value for blocknumber: 32
old   4: AND  &BlockNumber BETWEEN
block_id AND block_id + blocks -1
new   4: AND  32 BETWEEN block_id AND
block_id + blocks -1

OWNER      SEGMENT_NAME        SEGMENT_TYPE
------------
------------------------- ------------------
SCOTT      EMP         TABLE

SYS@ora10g>

SYS_S:191_P:5773_ora11g> select * from v$waitstat order by 1;

CLASS   COUNT     TIME
------------------ ---------- ----------
1st
level bmb      0        0
2nd level bmb      0        0
3rd level bmb     
0        0
bitmap block      0        0
bitmap index block     0       
0
data block      0        0
extent map      0        0
file header
block    60      240
free list      0        0
save undo block     
0        0
save undo header     0        0
segment header      0       
0
sort block      0        0
system undo block     0        0
system
undo header     0        0
undo block      0        0
undo header     
1        0
unused       0        0

18 rows selected.