Monday, July 25, 2011

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.

Thursday, July 7, 2011

Sofware Management Antipatterns: E-Mail is Dangerous

Using e-mail is an important communication tool in software companies, but performing communications mostly with e-mail is dangerous. In this post, this issue will be detailed together with common e-mail mistakes. This information can be generalized for most types of companies.

E-mails may be used for some kind of situations:
  • For sending a report, meeting record etc. which is not confidential, to a manager or a group.
  • For sending a short message which is not urgent, to a person who can’t be accessed via telephone and face-to-face.
E-mails should NOT be used for these situations:
  • For confidential messages and criticisms: E-mails can be distributed to other people or large groups easily, so this is not a good idea.
  • For situations  which could be used as evidence in a court of law : For example, if you say “We will do X item in a month” to the customer with e-mail, it can be a mandatory item for you in the next days.
  • For explaining a complex topic: It will be time consuming to write hundreds of words. Speaking will be more effective.
  • For explaining an important, sensitive topic: Word emphasis, voice tone, gestures and mimics are very important for conversations. E-mails have none of them and this may cause misunderstandings.

And some e-mail suggestions:

  •  Don’t use e-mail bodies as title, this is ridiculous:
Title: Please send me a report about X task.
Body: nothing
    •  Don’t put hundreds of people to your e-mail’s “TO” or “CC” list. Use BCC. Otherwise all people and spam softwares will know all e-mails:,, ... ,, …,
      • Don’t use infinite forwards for e-mails. These type of mails are not funny for most people.
      To: hundreds of people
      Title: FW:FW:FW:FW:FW:FW:FW:FW:FW:…
        • Don’t use e-mails as FTP. Use a file transfer protocol for sending messages larger than a few MB. A common wrong usage:
        Attachments: AnImportantDocument.pdf (123 MB)

        • Don’t use e-mails as a version controlling system. Manage your documents with a real version controlling system:
        Attachments:  “CustomerReport_last_20122010_newest_veryVeryLast_1_1.doc”.

        • Don’t use so many smiley images, big signature images, long signatures, colorful decoration templates in your e-mail. These are generally disgusting and unnecessary. Besides, they will increase network load.