Oracle的逻辑结构(表空间、段、区间、块)——Oracle数据块（二）

原创于2009年02月10日，2009年10月22日迁移至此。

以下脚本来自于互联网，具体出处已经找不到了，如有知道还请告知！

ITPUB个人空间 kHa/Q7K0r!F

关于热点块的查询


?4aO%C1c?Tp-k6C6517

====
查询当前数据库

最繁忙的
Buffer
，
TCH(Touch)
表示访问次数越高，热点快竞争问题就存在
=====

SELECT *

FROM
(SELECT addr, ts#, file#, dbarfil,
dbablk, tch

FROM x$bh

ORDER BY tch DESC)

WHERE
ROWNUM < 11;



====
查询当前数据库最繁忙的
Buffer
，结合
dba_extents
查询得到这些热点
Buffer
来自哪些对象
=====

SELECT e.owner, e.segment_name,
e.segment_type

FROM dba_extents e,

(SELECT *

FROM (SELECT addr, ts#, file#, dbarfil, dbablk, tch

FROM x$bh

ORDER BY tch DESC)

WHERE ROWNUM < 11) b

WHERE e.relative_fno = b.dbarfil

AND e.block_id <= b.dbablk

AND e.block_id + e.blocks > b.dbablk;



=============
如果在
Top 5
中发现
latch free
热点块事件时，可以从
V$latch_children
中查询具体的子
Latch
信息
============

SELECT *

FROM
(SELECT addr, child#, gets, misses,
sleeps, immediate_gets igets,

immediate_misses imiss,
spin_gets sgets

FROM v$latch_children

WHERE NAME = 'cache buffers chains'

ORDER BY sleeps DESC)

WHERE
ROWNUM < 11;



================
获取当前持有最热点数据块的
Latch
和
buffer
信息
==========

SELECT b.addr, a.ts#, a.dbarfil, a.dbablk,
a.tch, b.gets, b.misses, b.sleeps

FROM
(SELECT *

FROM (SELECT addr, ts#, file#,
dbarfil, dbablk, tch, hladdr

FROM x$bh

ORDER BY tch DESC)

WHERE ROWNUM < 11) a,

(SELECT addr, gets, misses, sleeps

FROM v$latch_children

WHERE NAME = 'cache buffers chains') b

WHERE
a.hladdr = b.addr;



===============
利用前面的
SQL

可以找到这些热点
Buffer
的对象信息
===========

SELECT distinct e.owner, e.segment_name,
e.segment_type

FROM dba_extents e,

(SELECT *

FROM (SELECT addr, ts#, file#, dbarfil, dbablk, tch

FROM x$bh

ORDER BY tch DESC)

WHERE ROWNUM < 11) b

WHERE e.relative_fno = b.dbarfil

AND e.block_id <= b.dbablk

AND e.block_id + e.blocks > b.dbablk;



================
结合
SQL
视图可以找到操作这些对象的相关
SQL
，然后通过优化
SQL
减少数据的访问，

或者优化某些容易引起争用的操作（如
connect by
等操作）来减少热点块竞争
=================



break on hash_value skip 1

SELECT /*+ rule */ hash_value,sql_text

FROM v$sqltext

WHERE (hash_value, address) IN (

SELECT a.hash_value, a.address

FROM v$sqltext a,

(SELECT DISTINCT a.owner,
a.segment_name, a.segment_type

FROM dba_extents
a,

(SELECT
dbarfil, dbablk

FROM (SELECT dbarfil, dbablk

FROM x$bh

ORDER BY tch DESC)

WHERE
ROWNUM < 11) b

WHERE a.relative_fno
= b.dbarfil

AND a.block_id
<= b.dbablk

AND a.block_id
+ a.blocks > b.dbablk) b

WHERE a.sql_text LIKE '%' || b.segment_name || '%'

AND b.segment_type = 'TABLE')

ORDER BY hash_value, address, piece;

^.}RF:q$X6517

也可以参看 热点块竞争和解决（cache buffers chains）

http://blog.oracle.com.cn/html/32/203732-4268.html