Database compatibility
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The document discusses migrating a database table's column from storing percentage values in the range of 0 to 100 to storing decimal values in the range of 0 to 1, without downtime or changing the database schema. It proposes doing this by adding a new column to store the decimal values, populating it from the existing percentage column, then dropping the original column and modifying the new one to be the main value column. This allows applications to continue reading and writing as normal during the migration.
![DB: DogfightingTable users with two columns id and valueValue is a percentage, stored as [0, 100]Migrate to [0, 1] representationClustered servers talking to the DBNo downtimeCompany Confidential - Wealthfront Inc.](https://image.slidesharecdn.com/dbcompatibility-forexport-110301132919-phpapp02/85/Database-compatibility-3-320.jpg)
![DB: DogfightingCompany Confidential - Wealthfront Inc.Reads id & valueWrites [0, 100] in valuecreate table users ( id int not null, value int not null);](https://image.slidesharecdn.com/dbcompatibility-forexport-110301132919-phpapp02/85/Database-compatibility-4-320.jpg)
![DB: DogfightingCompany Confidential - Wealthfront Inc.Reads id & valueWrites [0, 100] in valueWrites [0, 1] in value_dec](https://image.slidesharecdn.com/dbcompatibility-forexport-110301132919-phpapp02/85/Database-compatibility-6-320.jpg)
![DB: DogfightingCompany Confidential - Wealthfront Inc.Reads id & value_decWrites [0, 1] in value_dec](https://image.slidesharecdn.com/dbcompatibility-forexport-110301132919-phpapp02/85/Database-compatibility-8-320.jpg)
![DB: Top GunTable users with two columns id and valueValue is a percentage, stored as [0, 100]Migrate to [0, 1] representationClustered servers talking to the DBNo downtimeNo DDL change (value is decimal)Company Confidential - Wealthfront Inc.NEW](https://image.slidesharecdn.com/dbcompatibility-forexport-110301132919-phpapp02/85/Database-compatibility-10-320.jpg)
Database compatibility
- 1. Database compatibility(i.e. Application talking to a DB)Select statementApp. is reader, DB is writerInsertApp. is writer, DB is readerCompany Confidential - Wealthfront Inc.
- 2. DB: Rules of EngagementAdding a table: ✔Removing a table: ✔Table is unusedRemoving a column: ✔Column is unusedAdding a column: ✔NullableORNot-null with default valueRenaming a column: ✖Company Confidential - Wealthfront Inc.
- 3. DB: DogfightingTable users with two columns id and valueValue is a percentage, stored as [0, 100]Migrate to [0, 1] representationClustered servers talking to the DBNo downtimeCompany Confidential - Wealthfront Inc.
- 4. DB: DogfightingCompany Confidential - Wealthfront Inc.Reads id & valueWrites [0, 100] in valuecreate table users ( id int not null, value int not null);
- 5. DB: DogfightingCompany Confidential - Wealthfront Inc.alter table users modify value int, add value_dec decimal;
- 6. DB: DogfightingCompany Confidential - Wealthfront Inc.Reads id & valueWrites [0, 100] in valueWrites [0, 1] in value_dec
- 7. DB: DogfightingCompany Confidential - Wealthfront Inc.update users set value_dec = value / 100 where value_dec is null;
- 8. DB: DogfightingCompany Confidential - Wealthfront Inc.Reads id & value_decWrites [0, 1] in value_dec
- 9. DB: DogfightingCompany Confidential - Wealthfront Inc.alter table users drop column value, modify value_dec decimal not null;
- 10. DB: Top GunTable users with two columns id and valueValue is a percentage, stored as [0, 100]Migrate to [0, 1] representationClustered servers talking to the DBNo downtimeNo DDL change (value is decimal)Company Confidential - Wealthfront Inc.NEW