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When working with clients, a common question arises: "Which standby type best suits our high availability needs?" Before answering, we ensure clients fully understand each standby concept and provide necessary guidance.
Standby servers are replicas of the primary database that can take over during failures. PostgreSQL offers multiple standby configurations, each with distinct use cases and trade-offs. This post examines three types: cold, warm, and hot standby.
1. Standby Types
1.1 Cold Standby
A cold standby server remains powered off or inactive until needed after a primary failure. It relies on periodic backups or filesystem snapshots.
Activation: Manual backup restoration or server activation.
1.2 Warm Standby
A warm standby continuously receives WAL (Write-Ahead Logging) files from the primary but doesn't process application queries. It remains in recovery mode, applying WAL updates.
Activation: Manual promotion via failover.
1.3 Hot Standby
A hot standby actively streams WAL data near-real-time and supports read-only queries while applying changes. Ideal for offloading reporting workloads.
Activation: Automatic promotion during failures.
2. Comparison: Pros, Cons & Use Cases
3. Conclusion
Choosing the right standby depends on business needs:
- Cold: Low cost → Non-critical systems
- Warm: Moderate recovery → Disaster recovery
- Hot: Minimal downtime → Mission-critical production
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