What Is a Zero-Downtime Schema Change?
A zero-downtime schema change modifies a database that is serving live traffic without taking the application offline. It relies on non-blocking or online operations and backward-compatible steps so reads and writes continue throughout. Techniques like expand-contract and online table rebuilds make the change invisible to users.
Why it matters
Naive schema changes can lock a table and stall every query until they finish, causing an outage. Online, compatible techniques let teams evolve the schema while the service keeps running.
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