Domain 4 of 4 · Chapter 3 of 4

Cost-Optimized Databases

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Included in this chapter:

  • ElastiCache Reserved Nodes: payment options and break-even math
  • Aurora Serverless v2 ACU pricing vs provisioned RI — the utilization curve
  • DynamoDB on-demand vs provisioned: the utilization break-even
  • Worked example: ElastiCache on-demand → Reserved Node transition

Database cost optimization mechanisms by service

ServiceCommitment mechanismVariable-load mechanismCaching layer benefit
RDS (MySQL, PostgreSQL, etc.)RDS Reserved Instances (1/3 yr)Stop instance up to 7 daysElastiCache for read offload
AuroraAurora Reserved InstancesAurora Serverless v2 (ACU-based autoscaling)ElastiCache for hot keys
DynamoDBReserved Capacity (provisioned mode)On-demand modeDAX for read-through cache
ElastiCache (Redis, Memcached, Valkey)Reserved Nodes (1/3 yr)Serverless mode (ECPU-based)N/A (it's the cache)
RedshiftReserved Nodes (1/3 yr)Serverless (RPU-based)Result-set cache built-in
Cheat sheet

Cheat sheet

  • Predictability picks the pricing model
  • Caching reduces required database tier
  • DynamoDB on-demand vs provisioned: utilization-driven trade-off
  • Aurora Serverless v2 break-even ≈ 50% utilization
  • ElastiCache Reserved Nodes: same payment options as EC2 RIs
  • RDS instances can be stopped for up to 7 days
  • Lazy-loading vs write-through: pick by hot-key tolerance
  • Aurora I/O-Optimized: predictable cost when I/O is heavy
  • ElastiCache Serverless: auto-scales without capacity planning, pay-per-use, Valkey is 33% cheaper
  • ElastiCache data tiering (R6gd): hot data stays in memory, cold data moves to NVMe SSD — 60 %+ savings when ≤20 % is hot
  • Customer-managed KMS key: ~$1/key/month + per-request
  • Aurora Serverless v2: ACU autoscaling in 0.5-ACU increments

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Also tested in

References

  1. RDS Reserved DB Instances
  2. Aurora Serverless v2
  3. DynamoDB read/write capacity mode
  4. ElastiCache Reserved Nodes
  5. Stopping an RDS instance
  6. What is Amazon ElastiCache
  7. DynamoDB Accelerator (DAX)
  8. Amazon DynamoDB on-demand pricing
  9. DynamoDB Reserved Capacity
  10. Aurora I/O-Optimized vs Standard
  11. https://aws.amazon.com/kms/pricing/
  12. Amazon ElastiCache pricing
  13. Amazon Aurora pricing