You need to split full_name into first_name and last_name on a busy table, while old app versions keep reading full_name. Which order does it with no downtime and no broken readers?

Options

• ✗ Rename the column in one ALTER TABLE, then deploy the new code
• ✗ Deploy code that reads the new columns, then add them
• ✓ Add the new columns, write both, backfill old rows, switch reads, and drop full_name once nothing reads it Correct
• ✗ Copy the table, swap the names in a transaction, and drop the old one

Why

This is expand and contract. Expanding (new nullable columns, dual writes) is additive, so old code keeps working. The backfill fills the rows written before the dual writes began. Reads switch only once every row has the new shape, and the contract step drops the old column only after the last reader of it is gone. Each step is its own deploy and can be rolled back until the drop. A one-shot rename locks a big table and breaks every reader of the old name at once.

Review this in your daily deck → All cards in Databases