2010-02-22 Mon

23:35 Thinking Clearly About Performance, revised to include Skew (564 Bytes) » Cary Millsap

I’ve just updated the “Thinking Clearly” paper to include an absolutely vital section that was, regrettably, missing from the first revision. It’s a section on the subject of skew.

I hope you enjoy.

22:08 基于CNZZ计数器的浏览器分布统计 [Flickr] (556 Bytes) » 车东[Blog^2]

车东@FlickR posted a photo:

data.cnzz.com/main.php?s=brow_detail&brow=360SE&s...

20:19 回顾过去，展望未来——09年年会 (256 Bytes) » SNC IT Service

回顾过去，展望未来，09年年会于1月29日在广州鹿鸣酒家举行。为答谢oracle和ibm过去一年对我们公司的帮助，及来年对我们的继续支持，我们诚意邀请了他们参加我们的年会。随着公司人员在...

18:08 Alibaba招聘信息安全专员（英文编审方向） (2058 Bytes) » Fenng's shared items in Google Reader

所在部门：
阿里巴巴－网络贸易安全部－知识产权保护部

招聘人数：4

岗位描述：
1、负责对英文网站违禁信息的审核和控制，保证网站信息的时效性和安全性。
2、通过审核，把握违禁信息的特点和趋势，优化网站的控制规则。
3、通过多种渠道和方法，发现和减少前台信息存在的问题和风险。

岗位要求：
1、本科以上学历，英语6级以上、读写流利（英语专业优先考虑）；MS Office操作熟练
2、细致耐心，责任心强，能承受压力；有敏锐的风险意识，善于发现和解决问题
3、有法律知识或相关工作背景优先考虑
4、能适应轮休制（做5休2）

本岗位工作地点在杭州滨江阿里巴巴园区，性质为外包（组织人事关系隶属中智经济技术服务有限公司）。

请将简历发送到：dbanotes@gmail.com 注明申请的岗位

1 票

15:54 SMON: recover undo segment 与事务恢复 (5467 Bytes) » Oracle Life

作者：eygle 发布在 eygle.com

在一些系统异常之后，尤其是异常Down机之后，数据库里可能会看到类似如下的提示信息：

SMON: about to recover undo segment 23
SMON: mark undo segment 23 as available

这些信息意味着，数据库需要这些回滚段的信息去恢复一些未完成事务，多数情况下，这些事务都能够得到恢复，但是如果不幸，在异常宕机时丢失了部分Write操作，则可能无法完成恢复，出现灾难。

以下一段日志来自生产数据库的日志恢复：

SMON: about to recover undo segment 23
SMON: mark undo segment 23 as available
SMON: about to recover undo segment 24
SMON: mark undo segment 24 as available
SMON: about to recover undo segment 25
Dead transaction 0x0019.01b.00009fc7 recovered by SMON
SMON: mark undo segment 25 as available
SMON: about to recover undo segment 26
SMON: mark undo segment 26 as available
SMON: about to recover undo segment 27
SMON: mark undo segment 27 as available

在这些日志中可以看到，Oracle在恢复一个死事务，0x0019.01b.00009fc7，这个事务使用的回滚段是0x19号，也就是25号回滚段，可以看到在随后的日志中，Oracle启用25号回滚段。

这就是由事务恢复引发的回滚段操作，以下日志可以作为类似的参考：

Dead transaction 0x0044.010.00007746 recovered by SMON
SMON: mark undo segment 68 as available
SMON: about to recover undo segment 69
SMON: mark undo segment 69 as available
SMON: about to recover undo segment 70
SMON: mark undo segment 70 as available
SMON: about to recover undo segment 71
SMON: mark undo segment 71 as available
SMON: about to recover undo segment 72
SMON: mark undo segment 72 as available
SMON: about to recover undo segment 75
SMON: mark undo segment 75 as available
SMON: about to recover undo segment 76
SMON: mark undo segment 76 as available
SMON: about to recover undo segment 77
SMON: mark undo segment 77 as available
SMON: about to recover undo segment 78
SMON: mark undo segment 78 as available
SMON: about to recover undo segment 79
Dead transaction 0x004f.00e.00005d5e recovered by SMON
SMON: mark undo segment 79 as available
SMON: about to recover undo segment 81
SMON: about to recover undo segment 120
SMON: mark undo segment 120 as available
SMON: about to recover undo segment 122
Dead transaction 0x009a.006.00003056 recovered by SMON
SMON: mark undo segment 154 as available
SMON: about to recover undo segment 156
SMON: mark undo segment 156 as available

某些恢复可能需要很长的时间，在此期间的一些异常可能导致SMON Crash，进而数据库Instance崩溃。
Oracle的一些内部事件允许设置debug_mode，以便允许在AUM模式下，手工进行回滚段的处理：

alert session set "_smu_debug_mode"=4;
alert rollback segment "_SYSSMU10$" ONLINE;

了解这些手段，但是需要谨慎使用，特别是当你决定DROP某个回滚段时。

设置10513事件，可以阻止SMON在启动数据库后执行恢复，这可以给我们一些诊断时间，在参数文件中如下设置：
event = 10513 trace name context forever,level 2

总之，和UNDO相关的操作极度危险，在一些金融领域，任何一个丢失的事务都可能成为灾难，所以了解任何一个动作及其可能带来的影响是对我们的重大考验。

判断永远比操作更重要！

-The End-

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11:59 心收静里寻真乐眼放长空得大观 (2204 Bytes) » 知道分子

送一副王冬龄老师写的对联，给大家拜年。

11:58 [IT Club] BI Data Warehousing in Healthcare (3792 Bytes) » 木匠 Creative and Flexible

通知:

From Adam,

I'm currently working with VIHA as part of the BI Data Warehousing team. I've also recently completed a project looking at the effective use of quantitative information in healthcare administration. As information needs, and the technologies available to support them, are continually changing, its an interesting field to be in.

I will talk a little bit about tools (Cognos, SQL Server & SSIS) we use and methodologies (relational & star schemas). I'd also like to share with you about some of the challenges we've faced in designing and building the data warehouse, as well as around what we're attempting around metadata and data quality feedback loops.

If we have time, it would also be good to look at the different types of analysis and reporting one needs support with data, - and on their implications for data warehouse design and development work.

Have a good Friday, - and I'll look forward to seeing you on Saturday.

Adam

时间: Feb 20 (Saturday) 2:30pm
地址 Address: 2121 Cedar Hill Cross Rd.

欢迎各位IT同仁.

Victoria IT Club hold free IT Seminars on 3rd Saturday 2:30pm every month at EBC church second floor meeting room.

11:58 Chinese new year lunch and welcome newbie 虎年吉祥 (7118 Bytes) » 木匠 Creative and Flexible

仅供娱乐,以下邮件转自鄙人对新员工的"敲诈"信.

各位华人同乡,

首先祝各位虎年虎虎生威,早日发达!

然后呢,

本公司华人社团(非黑帮)有一个传统,每位新人可以自愿请各位老员工吃一顿午饭.

离职跳槽高就的老员工,再自愿回请一顿,这样就平衡了.

再次声明,纯属自愿,愿者上钩.

Samuel Chen and Tina Chang你们两个联合请一次就行了.

北大才子Bill饭量特别大,所以要趁他回国在外,抓紧时间.

推荐: Raymond川菜. Future Shop旁边.

时间: 本周五中午, 或者下周五中午.