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！
关于热点块的查询
====
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;
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