Thoughts, terms, and ideas I’ve come across over the last few months.

• 5 questions to ask when creating tests:
  • What if null?
  • What if zero?
  • What if one item?
  • What if three items? (Bugs often show up on middle rows not the first/last)
  • What if many items?
• Don’t add cross-cutting concerns via inheritance. If you extend a class to add support for logging/caching you are adding a new responsibility (violating SRP).
• Update performance suffers from denormalization. When you update a duplicated value on a 1NF table you will have to update every row that has that value instead of just one row in 3NF. Solutions:
  • Don’t update - It’s not a problem if you are only inserting into an OLAP database.
  • Normalize your schema (3NF) - Why are you updating a denormalized data warehouse style database?
  • Accept inconsistent data - Update a few rows at a time in a commit.
  • Accept locking penalty - Page/Row locks will have to be taken out for the row being updated potentially blocking other sessions.
• Normalized Schema
  • Less storage used
  • Affect fewer records when updating
• Denormalized Schema
  • Possibly better at PK lookups as you may only need to hit one table.
  • Suffers from concurrency and deadlock issues if updating.
• Distributed Consensus Algorithm - Agreement on a single value by multiple nodes.