20 Database Design Best Practices

1. Use well defined and consistent names for tables and columns (e.g. School, StudentCourse, CourseID ...).
2. Use singular for table names (i.e. use StudentCourse instead of StudentCourses). Table represents a collection of entities, there is no need for plural names.
3. Don’t use spaces for table names. Otherwise you will have to use ‘{‘, ‘[‘, ‘“’ etc. characters to define tables (i.e. for accesing table Student Course you'll write “Student Course”. StudentCourse is much better).
4. Don’t use unnecessary prefixes or suffixes for table names (i.e. use School instead of TblSchool, SchoolTable etc.).
5. Keep passwords as encrypted for security. Decrypt them in application when required.
6. Use integer id fields for all tables. If id is not required for the time being, it may be required in the future (for association tables, indexing ...).
7. Choose columns with the integer data type (or its variants) for indexing. varchar column indexing will cause performance problems.
8. Use bit fields for boolean values. Using integer or varchar is unnecessarily storage consuming. Also start those column names with “Is”.
9. Provide authentication for database access. Don’t give admin role to each user.
10. Avoid “select *” queries until it is really needed. Use "select [required_columns_list]" for better performance.
11. Use an ORM (object relational mapping) framework (i.e. hibernate, iBatis ...) if application code is big enough. Performance issues of ORM frameworks can be handled by detailed configuration parameters.
12. Partition big and unused/rarely used tables/table parts to different physical storages for better query performance.
13. For big, sensitive and mission critic database systems, use disaster recovery and security services like failover clustering, auto backups, replication etc.
14. Use constraints (foreign key, check, not null ...) for data integrity. Don’t give whole control to application code.
15. Lack of database documentation is evil. Document your database design with ER schemas and instructions. Also write comment lines for your triggers, stored procedures and other scripts.
16. Use indexes for frequently used queries on big tables. Analyser tools can be used to determine where indexes will be defined. For queries retrieving a range of rows, clustered indexes are usually better. For point queries, non-clustered indexes are usually better.
17. Database server and the web server must be placed in different machines. This will provide more security (attackers can’t access data directly) and server CPU and memory performance will be better because of reduced request number and process usage.
18. Image and blob data columns must not be defined in frequently queried tables because of performance issues. These data must be placed in separate tables and their pointer can be used in queried tables.
19. Normalization must be used as required, to optimize the performance. Under-normalization will cause excessive repetition of data, over-normalization will cause excessive joins across too many tables. Both of them will get worse performance.
20. Spend time for database modeling and design as much as required. Otherwise saved(!) design time will cause (saved(!) design time) * 10/100/1000 maintenance and re-design time.

Read more: http://www.javacodegeeks.com/2012/02/20-database-design-best-practices.html#ixzz1lZ2GPfDI

50 Most Frequently Used UNIX / Linux Commands (With Examples)

http://www.thegeekstuff.com/2010/11/50-linux-commands/

1. tar command 

2. grep command 

3. find command 

4. ssh command 

5. sed command

6. awk command 

7. vim command 

8. diff command 

9. sort command

10. export command

11. xargs command

12. ls command 

13. pwd command

14. cd command

15. gzip command 

16. bzip2 command 

17. unzip command

18. shutdown command

19. ftp command

20. crontab command

21. service command 

22. ps command

23. free command

24. top command

25. df command

26. kill command

27. rm command

28. cp command

29. mv command

30. cat command

31. mount command

32. chmod command

33. chown command 

34. passwd command

35. mkdir command

36. ifconfig command

37. uname command 

38. whereis command 

39. whatis command

40. locate command

41. man command

42. tail command

43. less command

44. su command 

45. mysql command

46. yum command

47. rpm command

48. ping command 

49. date command

50. wget command 

ORA-12704: character set mismatch

Problem
As I execute this SQLstatement

1:  SELECT .....(ignore)  
2:      CASE   
3:        WHEN NIGT001.TAX_CD='15'  
4:          THEN (SELECT NIGT007.ADTR_NM  
5:             FROM NIGT007   
6:             WHERE NIGT001.PRST_ADTR_CD = NIGT007.ADTR_STAFF_CD(+) )  
7:       ELSE ''  
8:      END AS ADTR_NM  
9:  FROM NIGT001,NIGT013,NIGT007, ......(ignore)     
10:  WHERE ......(ignore)  
11:  ORDER BY .....(ignore)  

It showed this error message

ORA-12704: 字元設定不符合
12704. 00000 -  "character set mismatch"
*Cause:    One of the following
           - The string operands(other than an nlsparams argument) to an
           operator or built-in function do not have the same character
           set.
           - An nlsparams operand is not in the database character set.
           - String data with character set other than the database character
           set is passed to a built-in function not expecting it.
           - The second argument to CHR() or CSCONVERT() is not CHAR_CS or
           NCHAR_CS.
           - A string expression in the VALUES clause of an INSERT statement,
           or the SET clause of an UPDATE statement, does not have the
           same character set as the column into which the value would
           be inserted.
           - A value provided in a DEFAULT clause when creating a table does
           not have the same character set as declared for the column.
           - An argument to a PL/SQL function does not conform to the
           character set requirements of the corresponding parameter.
*Action:
第 97 行, 資料欄: 133 發生錯誤

Root Cause
The problem result from NIGT007.ADTR_NM is NVARCHAR2. 
But the case-when-else statement return empty string in else statement. The empty string is VARCHAR2. 
That's why it complains "character set mismatch". What we need to do is do casting.

1:  SELECT .....(ignore)  
2:      CASE   
3:        WHEN NIGT001.TAX_CD='15'  
4:          THEN (SELECT NIGT007.ADTR_NM  
5:             FROM NIGT007   
6:             WHERE NIGT001.PRST_ADTR_CD = NIGT007.ADTR_STAFF_CD(+) )  
7:       ELSE CAST('' as NVARCHAR2(10))  --do cast here
8:      END AS ADTR_NM  
9:  FROM NIGT001,NIGT013,NIGT007,, ......(ignore)    
10:  WHERE ......(ignore)  
11:  ORDER BY .....(ignore)  

4 tips to improve performance of Java application with database

Java database performance tips 1:

Find out how many database calls you are making and minimize those believe it or not if you see performance in seconds than in most cases culprit is database access code. since connecting todatabase requires connections to be prepared, network round trip and processing on database side, its best to avoid databasecall if you can work with cached value. even if your application has quite dynamic data having a short time cache can save many database round trip which can boost your java applicationperformance by almost 20-50% based on how many calls got reduced. 

Java database performance tips 2:

Check whether your database has indexed on columns if you are reading from database.

Java database performance tips 3:

Use PreparedStatement or Stored Procedure for executing query Prepared Statements are much faster than normal Statement object as database can pre-compile them and also cache there query plan. 

Java database performance tips 4:

Use Connection Pool for holding Database Connections. 

Reference: http://javarevisited.blogspot.com/2012/01/improve-performance-java-database.html

Java Comparator Example

If you have a List of the employee objects then you need to use Collections.sort() method to sort the list holding employee objects. Below example will show how to write custom comparator. I’ve given three examples of custom comparators.

Employee Object

Next you need to define the custom comparator which will help you to sort by employee name, gender and age.

Name comparator

Gender Comparator

Age Comparator

 Here is the main class which uses the comparator to sort the employee objects based on name, gender and age.

 The default result is based your insertion order.

If you apply NameComarator

The result will be sorted based on name.

If you apply AgeComparator

The result will be sorted by age.

If you apply GenderComparator

The result will be sorted by gender

5 Skills for Tech Leads

1) Development

You should be a developer, and a good one.

2) Release Management

Your main job is to resolve needs and roadblocks (not to make sure that people are following any methodology).

3) Product Management

Prioritize, that's all. Then, you just have to work on the most important tasks from your list (which will also be small ones if you did your homework). 

4) Recruiting

Learn how to test people inside your team.

5) Managing People

Be honest and helpful. 

http://blog.assembla.com/assemblablog/tabid/12618/bid/70857/5-Skills-for-Tech-Leads.aspx

How Larry Page Changed Meetings At Google After Taking Over Last Spring

• Every meeting must have one clear decision maker. If there's no decision maker -- or no decision to be made -- the meeting shouldn't happen.

• No more than 10 people should attend.

• Every person should give input, otherwise they shouldn't be there.

• No decision should ever wait for a meeting. If a meeting absolutely has to happen before a decision should be made, then the meeting should be scheduled immediately.

Read more: http://www.businessinsider.com/this-is-how-larry-page-changed-meetings-at-google-after-taking-over-last-spring-2012-1#ixzz1jK8m4Hva

iReport 直式/橫式報表

需求
根據User所選擇要輸出橫式或直式的格式，分別輸出符合指定格式的報表

若user選擇列印格式為橫式

就輸出橫式報表

若user選擇列印格式為直式

就輸出直式報表

作法 - 橫式報表

由於iReport建立template後，default式Portrait，此時要手動去修改其page format

1. right click --> Page Format

2. Choose "Landscape" -- > OK

3. Change sucessfully

4. Drag and drop data field to template

作法 - 直式報表

1. Drag and drop data fields into template

2. Click each data field and go to change its property

3. Change "Rotation" property to "Right"

4. Check the result

Winners and Losers in Business Open-Source Software

Application Server/Web Server:

• Trending Up: Node.js and NGINX
• Trending Level: Tomcat and Apache HTTP Server
• Trending Down: JBoss and GlassFish

Frameworks:

• Trending Up: Rails
• Trending Level: Spring, Grails, Struts
• Trending down: (none)

Databases and Big Data:

• Trending Up: HBase, Hadoop, MongoDB
• Trending Level: MySQL, PostgreSQL
• Trending Down: CouchDB

http://www.dzone.com/links/r/winners_and_losers_in_business_opensource_software.html

How to create barcode in iReport

Here is a simple example to create barcode in iReport

Scenario
1. As user click "Preview" in iReport, it will show dialog to input
2. iReport will generate barcode in "Preview" mode

Process
1. File-->New

 2. Choose "Blank A4"-->Open this Template

 3. Give it a name, barcodeReport, and click Next

4. Click Finish

5. Right click --> Add Parameter

6. Assign "barcodeParam" as its parameter name

7. Show palette: Window-->Palette

8. Click Barcode, Drag and Drop to template

9. Choose "Code128A" as our barcode type, and click "Use Barbecue"

10. A barcode has displayed in our template

11. Click "..." button in "Code Expression"

12. Assign "barcodeParam" in "Code Expression"

13. Click "Preview" to switch into Preview Mode

14. Input random value in this popup window and click OK

15. iReport will generate barcode based on the value you inputed

16. Download barcode reader in your smart phone, iPhone, and scan it to do validation

IO Error: Size Data Unit (SDU) mismatch:oracle.net.ns.NetException: Size Data Unit (SDU) mismatch

Problem
As I would like to do query via JPA, I got this error message

IO Error: Size Data Unit (SDU) mismatch:oracle.net.ns.NetException: Size Data Unit (SDU) mismatch

Solution
This problem results from inappropriate JDBC jar file, just upgrade your JDBC jar file to 11.2.0.3.0 or above

11 Things every Software Developer should be doing in 2012

1. Get on Twitter
2. Read StackOverflow Daily
3. Start a Blog
4. Get out there
5. Carry around a modern phone
6. Embrace Mobile
7. Learn at least one design pattern
8. Set reachable goals each and every year
9. Learn a different programming language
10. Boost your confidence
11. Read Blogs/Programming Books/Magazine


http://michaelcrump.net/11-things-every-software-developer-should-be-doing-in-2012

Preventative medicine for Memory leaks in Java

How to avoid memory leaks?

    To avoid memory leaks, We must check our applications to make sure the below:

• Our app ought to release JDBC ResultSet, Statement, or connections.
• Our app ought to use a finally block to make sure the objects are released appropriately.
• Our app ought to release instance or resource objects that are stored in static tables and
• also perform clean up on serially reusable objects.
  For example, appending an error messages to a Vector defined in a serially reusable object. The app never cleaned the Vector before it was given to the next user. As the object was reused over and over again, error messages accumulated and causes a memory leak that will be difficult to track it down.

http://www.codedairy.com/bestpractices/preventative-medicine-for-memory-leaks-in-java#.TvzFwq_rHJ4.dzone

Improve Software Quality with Tools and Processes

1. Choose a suitable process model and apply it correctly, ex. agile, scrum, iterative and incremental
2. Control the version of each required source, ex.  SVN, CVS and TFS 
3. Track issues with easy-to-use tools, ex.  JIRA
4. Perform and manage documentation, ex.  Confluence
5. Use dependency management tools, ex.  Maven
6. Use continuous integration, ex.  Hudson
7. Perform testing and integration testing constantly, ex.  JUnit
8. Perform unit testing and automatize it, ex.  Hudson with Maven
9. Collect metrics from production and use results, ex.  CodePro Eclipse plug-in
10. Follow best practices of coding and control with tools, ex.  Maven Surefire Report plug-in

http://www.dzone.com/links/r/improve_software_quality_with_tools_and_processes.html

善用Oracle提供的function來提升系統效能

有關報表的日期欄位，資料庫是儲存成yyyMMDD or yyyMM。根據現有需求，需formatting成YYY/MM或者是YYY/MM/DD格式，因為效能考量，此類的formatting應在SQL裡頭做，不要放到AP level做。

舉個例子來說

• 屆滿年月
  • NVL2(NIGT001.APL_LIMIT_YM, SUBSTR(NIGT001.APL_LIMIT_YM,0,3)||'/'||SUBSTR(NIGT001.APL_LIMIT_YM,4,2), ' ')
• 作業日期
  • NVL2(NIGT001.PRST_PRCD_DATE, SUBSTR(NIGT001.PRST_PRCD_DATE,0,3)||'/'||SUBSTR(NIGT001.PRST_PRCD_DATE,4,2)||'/'||SUBSTR(NIGT001.PRST_PRCD_DATE,6,2), ' ')

 

Oracle相關語法簡介：

• NVL2 - http://www.techonthenet.com/oracle/functions/nvl2.php
• SUBSTR - http://www.techonthenet.com/oracle/functions/substr.php

 

Are You Making These 7 Productivity Mistakes?

Mistake #1: Cutting Back on Sleep
Mistake #2: Multi-Tasking
Mistake #3: Doing Everything Yourself
Mistake #4: Focusing Solely on Numbers
Mistake #5: Eating at Your Desk
Mistake #6: Checking Email Frequently
Mistake #7: Pushing Yourself Hard

http://www.dzone.com/links/r/are_you_making_these_7_productivity_mistakes.html

No output specified for the exporter

Problem
As I would like to export pdf via JasperReports JRExporter, it throw "No output specified for the exporter" exception.

Root Cause
I forgot to set OutputStream to JRExporter parameter, i.e.

1:  JRExporter pdfExporter = new JRPdfExporter();  
2:  pdfExporter.setParameter(JRExporterParameter.OUTPUT_STREAM, outputStream);  
3:  //........