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.