Database Cost Engineering: Rules of Thumb

Database costs sneak up. Five rules of thumb cap them without sacrificing performance.

Why DB costs sneak

Storage grows; instance class drifts up; backups accumulate; replicas pile on.

Without active management, DB cost compounds.

Five rules of thumb

• 1. Right-size instance class quarterly.
• 2. Tier old data to cheaper storage.
• 3. Prune unused indexes.
• 4. Cap backup retention.
• 5. Audit replicas for actual usage.

Per-rule savings

Right-size: 20-40%.

Tier old data: 50-80% on archived data.

Index prune: 5-15% storage + write speedup.

Backup retention: 30-50% of backup spend.

Replica audit: 10-30% replica spend.

Order of operations

Order: right-size first (highest impact). Then archive. Then index. Backups + replicas last.

Apply quarterly; the cumulative effect is large.

Antipatterns

• Database growth as inevitable. Mostly preventable.
• One-time cost cut. Drift returns.
• Cost vs performance as binary. Most fixes do both.

What to do this week

Three moves. (1) Apply this pattern to your most-loaded table. (2) Measure query latency / write throughput before/after. (3) Document the win and the constraint so the next refactor inherits the knowledge.