Geng Mao's Blog

GAppProxy + AutoProxy

2009-07-13T00:33:00.002+08:00

实在是受不了GFW，利用AppEngine帐号setup了一个GAppProxy。
很简单。再配合AutoProxy，可以自由访问blogger，facebook了。
唯一的困难是https还有问题，不能正常使用twitter。
有人已经有些思路。期待能够解决

two bad things for database server on linux

2009-04-19T00:05:00.003+08:00

Today saw a post about swappiness in pythian. It recalls my memory of tuning oracle on linux.
Linux is great, but not all things on linux are optimal for database. There are two bad things. One is swappiness, another one is file cache. If you run oracle on linux default, you may find the file system cache often grabs huge memory and system is busy in paging out oracle processes. It's too bad.
The solution is 1) setting swappiness to zero, it tells linux to release file cache instead of swapping processes to disk when memory is tight 2) use DIRECT_IO (no file system caching in db2), it bypass file cache so not suffers double-buffering.

32位系统上如何让Oracle数据库使用超过2G内存

2008-11-06T00:29:00.008+08:00

今天一个朋友问到这个问题，记录一下。

32位系统都有个地址空间的问题，它限制了可以使用的Oracle SGA大小。

32位Windows有两个boot设置:/3G允许进程使用3GB的用户地址空间;/PAE允许进程使用超过4GB的内存。
修改boot.ini如下，然后重启系统。
[boot loader]
timeout=30
default=multi(0)disk(0)rdisk(0)partition(1)\WINDOWS
[operating systems]
multi(0)disk(0)rdisk(0)partition(1)\WINDOWS="Windows Server 2003, Enterprise" /fastdetect /3G /PAE
如果启用/3G，可以设置Oracle SGA大小到接近3GB；如果启用/PAE，再设置use_indirect_data_buffer=TRUE和db_block_buffers，data buffer大小不受4GB限制，可以很大。

而32位Linux下增大SGA limits需要relink；设置ramfs和use_indirect_data_buffer可以支持很大的data buffer。

Get out of ORA-28002: the password will expire within n days

2008-09-02T17:29:00.000+08:00

Today, a colleage meet this ORA-28002 when starting Content Server. It's a bit annoying.
So try to find the way to get out of this error.

This post does great to explain the problem. While even followed its solution B, the ORA-28002 remains there.
Then from Metalink note 162818.1, "ORA-28002 On User Connection Immediately After PASSWORD_LIFE_TIME Changed", it is known that "Accounts that have entered their grace
period will have to change their passwords.", even though the PASSWORD_LIFE_TIME is set back to unlimited.
Final workaround is altering user's password to the previous one. It doesn't change password, but bypass the annoying password life management.

Steps to record:
1. check out the password limits set to the user.
SQL> select LIMIT, RESOURCE_NAME from dba_profiles where RESOURCE_NAME in 'PASSWORD_GRACE_TIME','PASSWORD_LIFE_TIME','PASSWORD_REUSE_MAX','PASSWORD_REUSE_TIME') and PROFILE=(select profile from dba_users where username=);

2. check out the profile of the user.
SQL> select profile from dba_users where username=;

3. alter the profile, set the limits to unlimited.
SQL> alter profile limit PASSWORD_LIFE_TIME UNLIMITED;
SQL> alter profile limit PASSWORD_GRACE_TIME UNLIMITED;

4. if the user has entered the grace period (ORA-28002 when login), the password has to be altered. Fortunately you need not really change it.
SQL> alter user identified by ;

That's all.

Virtualization is amazing

2008-08-05T18:20:00.004+08:00

I knew VMWare before. I even tried VMWare Workstation before. I thought virtualization tech is interesting, but performance-slow and resource-inefficiency.
Until now, I found that the new company proactively utilizes various VMWare products, such as ESX Server, Virtual Center and Lab Manager. They are awasome. Tremendous installation/setup time are saved. Repeated tasks are automated. Daily works are extremely simplied. Productivity are largely promoted.

Check out this video of Lab Manager. http://download3.vmware.com/demos/labmanager/

EMC buying VMWare is a great deal. Don't let it slip way.

Oracle to Acquire BEA Systems

2008-01-17T01:34:00.000+08:00

Oracle to Acquire BEA Systems
"The addition of BEA products and technology will significantly enhance and extend Oracle's Fusion middleware software suite," said Oracle CEO Larry Ellison.
终于把BEA买下来了，是个好事。一直觉得OC4J不咋的，希望WebLogic以后做为Fusion middleware的核心。

Pythian Group Blog » Blog Archive » Pythian Goodies: The Answer to Free Memory, Swap, Oracle, and Everything

2007-12-20T20:38:00.000+08:00

Pythian Group Blog » Blog Archive » Pythian Goodies: The Answer to Free Memory, Swap, Oracle, and Everything:

"# Linux Oracle servers must use HugePages.
# Being low on free memory is not an issue.
# Using DirectIO is important to maintaining a useful file system cache."

"If the system is capable of running 64-bit Linux then it should. Using the VLM workaround adds significant overhead to database cache access."

real world sql tuning tips

2007-11-08T17:08:00.000+08:00

1. only CBO. RBO is dead.
2. 90-9-1 stats methodology. Don't touch optimizer parameters, refine your stats!
3. check the cardinality, compare the optimizer estimated and the actual one.

SQL> alter session set statistics_level=all;
SQL>
SQL> select * from table(dbms_xplan.display_cursor(null,null,'allstats last'));you can also find actual plan with stats from v$sql_plan_statistics_all

4. notice when stats are not enough and optimizer exceptions

A tip for changing JDK used by JDeveloper

2007-10-09T10:10:00.000+08:00

Web Services on Drugs: Changing the version of JDK used by JDeveloper
In short, move (rename) the embedded JDK to another place. Then restart JDev.

How to find out JDBC statement leaks in Oracle

2007-09-21T14:46:00.000+08:00

Serious leaks can be identified with then following SQL (10g):
select oc.inst_id, oc.sid, oc.hash_value, oc.sql_text, count(*)
from gv$open_cursor oc
where sql_text not like 'COMMIT%'
group by inst_id, sid, hash_value, sql_text
having count(*) > 5
order by 5;

9i or belower use v$open_cursor instead of gv$open_cursor

Java packages management system

2007-07-27T18:54:00.000+08:00

Linux has RPM/APT, Mac has Fink, Ruby has RubyGems, why Java hasn't a good packages management system yet? Experienced Java developers know the "Jar-Hell". They know the difficulties to management the dependencies of various jar files. They know the problems when J2EE applications use different versions of common libraries...
Will this Jar-Hell be solved by JSR 277: Java Module System or anything else?

Text of Steve Jobs' Commencement address (2005)

2007-05-24T00:49:00.000+08:00

Text of Steve Jobs' Commencement address (2005)
Steve Jobs says:
...
You can't connect the dots looking forward; you can only connect them looking backwards. So you have to trust that the dots will somehow connect in your future. You have to trust in something — your gut, destiny, life, karma, whatever. This approach has never let me down, and it has made all the difference in my life.
...
Sometimes life hits you in the head with a brick. Don't lose faith. I'm convinced that the only thing that kept me going was that I loved what I did. You've got to find what you love. And that is as true for your work as it is for your lovers. Your work is going to fill a large part of your life, and the only way to be truly satisfied is to do what you believe is great work. And the only way to do great work is to love what you do. If you haven't found it yet, keep looking. Don't settle. As with all matters of the heart, you'll know when you find it. And, like any great relationship, it just gets better and better as the years roll on. So keep looking until you find it. Don't settle.
...
And most important, have the courage to follow your heart and intuition. They somehow already know what you truly want to become.

7 Habits For Effective Text Editing 2.0 - Google Video

2007-04-23T19:29:00.000+08:00

Basic rules:
find inefficiency; find a quicker way; make it a habit

Habit 1: Moving around quickly
/ to search
use * again and again. * - search for next
use folding

Habit 2: Don't type it twice
Ctrl-N - keyword completion
Omni-completion in Vim 7

Habit 3: Fix it when it's wrong
spellchecker in Vim 7
add new abbrevation - :iabbrev teh the
add keyword for spellcheck - : syntax keyword WordError teh

Habit 4: A file seldom comes alone
ways to find your old files.
:!ctags -R . generate tags for all files under current directory (and sub directory)
:tag init
:tnext
:grep "\\>" **/*.h
:cnext

Go to the file
gf

Habit 5: Let's work together
copy text from vi to Word or other editors.

Habit 6: Text is structured
how to go from warnings/errors to source
map
:cfile %

Habit 7: Sharpen the saw
keep on tuning the set of commands you use
folding
automatic indenting
Plugins
edit files over a network
advanced scripting

2007 Annual Dinner

2007-03-07T09:38:00.000+08:00

2007 Annual Dinner

It's a wonderful evening. People present a tons of funny staff, make everyone laugh all the time. Laddies' dance, Shui Hu video, YMCA, OOTV, Xiang Sheng brought by Frank & Minmin, song name guessing and Pascal's 'singing'... There are so many wonderful things, I couldn't count them all. I also showed my voice - not singing, but narrating in our team's stage play, In the Mood for Love. Fortunately I didn't ruin this, as the show was interrupted by applause dozens times :)

Someone said, Life is full, full of surprises. So, to be surprised, I took a 'first-class' seat this evening - right beside Pascal! Yeah, it's a real exciting & funny experience for me :) And, I picked a '018' number and wan a first-lass prize at Lucky Draw, an iPod shuffle! I am a lucky man :) I believe it's a sign of good fortune in 2007, year of pig. Wish everyone in OARDC have a fruitful piggy year too!

An awesome demo movie about integrating Forms & JSF!

2007-03-01T11:00:00.000+08:00

An awesome demo movie about integrating Forms & JSF!
It is created by Wilfred van der Deijl, from oraTransplant. He is also going to present his work in ODTUG 2007. Looking forward his great paper:)
www.oraTransplant.nl, it's a good site with many useful material of oracle develop tools. Why I didn't find it ealier?

I am not a Big Fan of Hate...

2006-10-29T23:49:00.000+08:00

I am not a Big Fan of Hate...
Wang Jian Shuo, a famous blogger from Shanghai, China, talk about his opinion about patriotism and hate. It's really touchable, I can't agree him more. Hate others is not a shape of love.

Worst practices when using Oracle JDBC Drivers

2006-10-25T10:17:00.000+08:00

AMIS Technology blog » Blog Archive » Worst practices when using Oracle JDBC Drivers - great presentation by Douglas Surber
Fortunately Oracle is really making his JDBC driver more standard. I always dislike the former ugly proprietary extensions. Anyway, these bad practices are very helpful.

immediate exception when insert duplicate unique key

2005-08-31T06:26:00.000+08:00

When 2 sessions simultaneously insert the same primary key value to a table, oracle will block the later session. After the first session is committed, oracle throws an ORA-00001 error: unique constraint ... violated error.
If you hope that oracle don't block insert sessions, you need to implement something using dbms_lock package. Using this, errors will immediately be thrown out when many sessions insert same primary key value, even if these 'insert' haven't be committed. There is an good example from Tom Kyte.
I had thought that 'read uncommitted' transaction isolation level will simply solve this problem. But Oracle doesn't support 'read uncommitted', it implements only 2 transaction isolation levels: read committed(default) and serializable.