易截截图软件、单文件、免安装、纯绿色、仅160KB

oracle mutex

An introduction to Mutexes in 10gR2
By Connie Green, Kumar Rajamani
from meetings with: Kumar Rajamani, Russell Green, Saureen Shah, Cecilia Gervasio and Connie Green
Introduction
This paper is intended as an introduction to mutexes.  It describes new concepts associated with mutexes, when mutexes are used, and related wait events and views.
Overview
A mutex, similarly to a latch, is a low-level serialization mechanism used to control access to a shared data structure in the SGA.  Serialization is required to avoid an object being:
? deallocated while someone is accessing it
? read while someone is modifying it
? modified while someone is modifying it
? modified while someone is reading it
Mutexes can be defined and used in many different ways.  For example:
? Each structure being protected by a mutex can have its own mutex (e.g. a parent cursor has its own mutex, and each child cursor has its own mutex)
? Each structure can be protected by more than one mutex, with each mutex protecting a different part of the structure
? A mutex can protect more than one structure
The mutex can either be stored within the structure it protects, or elsewhere.  Mutexes are usually dynamically created at the same time as the structure they protect.  If a mutex is embedded within the structure it protects, then it will be implicitly destroyed when the owning structure is freed.
Benefits of mutexes
Although mutexes and latches are both serialization mechanisms, mutexes have certain features latches do not.
Smaller and faster
Mutexes were introduced as an alternative to latches, as they are much faster to get, and smaller.  A mutex get is in the region of 30-35 instructions, compared to 150-200 instructions for a latch.  A mutex is around 16 bytes in size, compared to 112 bytes for a latch in 10.2 (in prior releases it was 200 bytes).  Some of the reduction in latch size was achieved by obsolet


相关文档:

关于oracle的表空间,分区表,以及索引的总结


表空间:
Oracle的UNDOTBS01.DBF文件太大的解决办法
1、.禁止undo tablespace自动增长
alter   database   datafile   'full_path\undotbs01.dbf'   autoextend   off;
2.-- 创建一个新的小空间的undo tablespace
create undo tablespace undotBS2 datafile ......

Redhat Linux oracle 10g em 按钮乱码解决

网上有很多资料,也是参考eygle的文档。
OS : Redhat AS 4 U5
DB : Oracle 10.2.0.3
1.修改jdk 下面的字体。
[oracle@rac2 db_1]$ cd $ORACLE_HOME/jdk/jre/lib/
[oracle@rac2 lib]$ mv font.properties font.properties_bak
[oracle@rac2 lib]$
[oracle@rac2 lib]$ cp font.properties.zh_CN.Redhat font.propertie ......

oracle jobs批处理语句

--oracle jobs批处理命令参考
qlplus /nolog
connect sys/lee as sysdba
--以下两句在sys(即具有dba权限的用户)用户下执行
show parameter job_queue_processes;
alter system set job_queue_processes=10;
exit
sqlplus /nolog
connect jcy/jcy
ALTER TABLE T_OA_AFFICHE MODIFY (INPUT_TIME DATE);
ALTER TABLE ......

oracle 的 left/right join与(+)的一个区别

基本从来不用left/right join
一个项目被迫要用别人写的 sql
本打算改写一下,提高效率
发现:
【1】
select * from  a
left outer join  b on a.id= b.id AND ...1...
 where ...2...

【2】
select * from  a , b 
 where a.id= b.id(+)
A ......

Oracle中把yyyy mm dd转成yyyy年mm月dd日


SQL> select   to_char(sysdate,'yyyy')||'年'||to_char(sysdate,'mm')||'月'||to_char(sysdate,'dd')||'日'  from   dual;
TO_CHAR(SYSDATE,'YYYY')||'年'|
或者使用双引号
select to_char(add_months(trunc(sysdate),-1),'yyyy"年"mm"月"') from dual    取上个月份
......
© 2009 ej38.com All Rights Reserved. 关于E健网联系我们 | 站点地图 | 赣ICP备09004571号