Change management of database scripts


In this post I’m going to discuss the strategy used by our team to manage the changes taking place in the database. Most of the time we as developers mainly focus on implementing the feature and put less effort on manage the database changes. For instance individual might not straight away see the importance in the first place and also this may not be very important for projects with smaller teams but for projects with a larger scope, involving multiple teams and frequency of changes in the functionality is high then might feel the importance of coming up with a strategy to manage this.

First lets try to identify situations that favours to coming up with a strategy for projects that requires to maintain a RDBMS as the data store.

  • For a project having multiple teams to carrying out the development.
  • For a project with a larger scope, having fortnight or monthly deliverables.
  • For a projects with a longer duration.
  • For projects having teams distributed across different geographic locations.

Above list might not be a complete one, so the reader is always welcome for suggestions. I’ll be taking the above scenarios as the base for the rest of my discussion. The obvious fact is that the change is inevitable. To accommodate this change almost every development team use version controlling to effectively mange the development carry out by each individual in the team. Similarly it’s best to come up with a strategy early in the development life cycle on managing the changes taking place to the database of the application(s). The changes can take place to the database under following categories:

  1. A way to keep track of the new insertions of table(s).
  2. A way to keep track of insertion, updates and deletion of column(s) in a table.
  3. A way to keep track of insertion, updates and deletion of row(s) in a table.
  4. A way to manage application configurations/fixed data mappings.
  5. A way to manage setting up of the database for fresh installation or upgrades.

Step 1

The Step 1 can be handled by maintaining a separate SQL script (lets name it db_tables.sql) to keep track of all the new insertion of table(s) into the application. Most of the situations inserting of new table(s) arises when there is a requirement to implement a new feature. So this would give a clear picture of the database about when and at which point in time each table got introduced and by whom.

Step 2 & 3

The Step 2 & 3 can be handled by maintaining a separate SQL script (lets name it db_tables_tracker.sql).

Step 4

In the Step 4, maintain individual SQL scripts to represent the data mapping of each identified table(lets name them as sys_config.sql, app_modules.sql, etc…), also the changes required by each can be introduced directly in to mapping itself or can be accommodated via db_tables_tracker.sql. For tables having larger number of records as data mapping it would be easier to alter the existing mappings to reflect the new change rather accommodating it via db_tables_tracker.sql. This way it helps an individual to get an idea of the most recent state of the mapping just by looking at the SQL script, this approach fails when the application required to main foreign key constraints among related tables because this approach requires to drop and reintroduce the table every time the update takes place on the table column(s) or to the data.

Step 5

The Step 5 can be elaborated by broken it down in to two.

Fresh installation of the database

To accommodate a fresh installation scenario of the database, all the SQL scripts created in first 4 steps can be combines into one batch by carefully arranging the SQL scripts as follows.

  • SQL script from step 1 – db_tables.sql
  • SQL script from step 2 & 3 – db_tables_tracker.sql
  • SQL scripts from step 4 – sys_config.sql, app_modules.sql, etc…

Note : Above sequence can be automated using a shell script (db_init.sh).

Upgrading of an existing database

For the purpose of preparing the database to accommodate new changes on to the existing table(s) we can maintain a new SQL script called db_upgrade_tracker.sql. This script will only hold the SQL statements required for updating the previous version of the database to the new state, taken from db_tables.sql and db_tables_tracker.sql scripts. Next step is to sequence the flow of the SQL scripts for the database upgrade as follows:

  • db_upgrade_tracker.sql
  • SQL scripts from step 4 – sys_config.sql, app_modules.sql, etc…

Note : Above sequence can be automated using a shell script (db_upgrade.sh).

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