Database migrations without downtime
Strategies for zero-downtime database migrations Downtime can hit users hard and hurt revenue. With careful planning, you can migrate databases with little or no interruption. The key is to combine non-blocking changes, continuous data sync, controlled cutover, and good monitoring. Start by mapping the most disruptive steps and then replace them with safer alternatives. Use non-blocking schema changes: add new columns with default NULL, avoid long-running locks. In PostgreSQL, create indexes concurrently; in MySQL, tools like gh-ost or pt-online-schema-change help minimize locks. Run dual writes and backfill data: keep old and new schema in sync during the transition. The app can write to both paths, then backfill existing rows in the background. Leverage replication and read traffic shifts: use read replicas to absorb load during the migration. Streaming replication keeps backups ready for a quick switch. Employ canary and blue-green rollout: run the new code path for a small user segment, then widen the exposure as confidence grows. Cutover with feature flags and clear rollback: toggle the new behavior behind a flag, monitor metrics, and roll back if problems appear. Validate with checks and safeguards: run row counts, checksums, and latency tests. Have a rollback plan and a tested, documented recovery path. Example approach to a common change: adding a new nullable field and then using a view to unify reads. ...