Why do Evolutionary Design or Iterative Design or Incremental Design? Everyone who has not worked in an evolutionary manner asks this? My answer, if you think the system you designed is NOT GOING TO CHANGE EVER then sure you can do design once and deploy once and you are done, move on to next project. But tell me one project you have been on, that does not have any changes in requirements, changes in technology, changes in look and feel etc after it was deployed.
ThoughtWorks is going to be at Oracle Open World. I’m excited about this especially since it will give ThoughtWorks and Me to talk about software practices and how to apply these software practices to the database development world, off course I will talk about my books Refactoring Databases and Continuous Database Integration. ThoughtWorks will have a booth at “343 Moscone South” and I will be there on Nov 14.
Recently talking to someone about a persistence framework that they are using, this framework creates a rows in the database table with just Primary Key value and then later on updates the table row with values for other columns. Because of this framework, the tables cannot have any NOT-NULL constraints defined.
On any machine running network related services like in my case Oracle Listener and Dispatch Services. Don’t rebuild/stop and restart the firewall stuff like iptables.
Had to spend a lot of time, figuring out what was going on. So hard lesson learnt don’t mess with iptables when you are running oracle listener/dispatcher
A question I get, mostly related to the evolutionary database design and development. When the pair (team) gets a new feature (story) to work on, the team looks at the existing table/database design and sees if the current design is enough to implement the feature they are working on. If the currency database design does support the feature they are trying to implement, then they do not have to change the database at all, they will move on to implement the feature and change the application code as necessary.
Currently working on a legacy application, thats been in production for a long time now. I wanted to find out what are the Tables and Columns being used by the application. Since we could see that some table columns where not being used. We are using a Object Relational mapping framework on the project, so we decided to write some code that would parse all the mapping files and gives us a list of table names and columns. We used this list to create rows in a table with two columns tablename and columnname. Once the table had this data, we just ran one more SELECT against the metadata of the database and our table which pretty much gave us a list of Table and Columns that we are not using
When you are refactoring large databases, you will have certain tables that have millions of rows, so lets say we are doing the Move Column refactoring, moving the TaxAmount column from Charge table which has millions of rows to TaxCharge table. Create the TaxAmount column in the TaxCharge table. Then have to move the data from the TaxAmount column in the Charge table to the TaxAmount column you created in the TaxCharge table.
When you are writing xUnit tests you are in certain ways trying to make sure that the test breaks when the code that is being tested changes the assumptions you made when writing the Test and Production code.
Similarly if you are relying on the database to throw a error when you put invalid data, then you should write a test around this assumption, so that when someone changes the database to not behave the way you assumed it to behave, the test you wrote will break and it will force the team to think about the change to the database that is being undertaken. If the change is really required, then the team would fix the test else rollback the change being made.
I will be presenting about Evolutionary Database Design and Database Refactoring at ThoughtWorks Master Class Series 2007 at Bangalore on May 19th and Pune on May 26. This will be the first time I will be presenting in India.