What are the steps to refactor an existing database schema without downtime?

Refactoring an existing database schema without causing downtime can be a complex process, especially for databases that are in active use. The goal is to make changes such as modifying structures, optimizing performance, or adding new features without disrupting the service. Refactoring a database schema without downtime requires careful planning, detailed testing, and meticulous execution. It’s crucial to involve all stakeholders (developers, DBAs, operations) throughout this process to ensure a smooth transition and continued integrity of the data.

In my experience, 1) Data migration in phased approach is very beneficial, move heavy volume of data from old schema to new schema a week before. 2)Then move data incrementally 3)On final day let the active transactions drain from application server side. 4)then point the application server to connect new DB =================== 0) copy structure and copy DB explain plans from old to new because even small character may create new plan at times it could be worse plan. Faced multiple times in my experience.

After reviewing the design modifications and data migration strategies. I found redefine online without any downtime strategy very helpful. Bold changes in your design may look scary, if the outcome/benefit weighs more in favor of simplicity, ease of use and efficiency, do it.

. Planning and Design Assess Current Schema: Understand the existing schema thoroughly. Identify potential issues and areas for improvement. Define Requirements: Clearly define what changes are needed. This might include adding new tables, changing data types, adding indexes, etc. Design New Schema: Create a detailed plan for the new schema. Consider how it will affect current queries and performance.

With Oracle Editioning (since Oracle 12.2), this is a straight-forward process. This process works at all levels, Dev, QA, UAT, Prod... 1) Implement the new edition of the schema. 2) Test the new edition of the schema. 3) Take out the new edition of the schema if it doesn't work. 4) Allow user connections to disconnect/reconnect to the new edition of the schema if it does work. 5) Remove the old edition of the scheme after all connections have transitioned.

1) Oracle Editioning (since Oracle 12.2) handles this automatically in the same database. A parallel database/environment is not required 2) If the current equipment can't handle the new schema, turn off the new schema and regroup/re-plan.

In Oracle Editioning (since Oracle 12.2), data migration occurs when you want. The old schema continues to function alongside the new schema in the same database until a complete transition is complete.

In Oracle Editioning (since Oracle 12.2), the switch-over can be delayed as long as needed. Each connection to the old schema will eventually go away and new connections will be made to the new schema. This transition can be organic, even during the highest traffic periods.

Continuous Monitoring and Optimization Monitor Database Logs and Performance Metrics: Keep an eye on performance issues that might surface after the changes. Optimize as Necessary: Based on the performance data, continue to make adjustments to indexes, queries, and configuration to optimize the new schema.