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Explain advanced database migration strategies in zero-downtime PHP systems at scale.
Updated May 24, 2026
Short answer
Zero-downtime migrations use backward-compatible schema changes, phased rollouts, and dual-write strategies to evolve databases without service interruption.
Deep explanation
In high-scale PHP systems, database schema changes are one of the highest-risk operations. Zero-downtime migration strategies ensure that production systems remain available while schema evolves.
Core principles:
- Backward compatibility first
- Additive changes only (new columns, nullable fields)
- Avoid destructive changes initially
- Expand–Contract pattern
- Expand: add new schema alongside old
- Migrate: dual-write or backfill
- Contract: remove old schema later
- Dual write strategy
- application writes to old and new schema simultaneously
4.…
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