Amazon RDS Vs DynamoDB: Which Database Will Cost You Less?

When comparing Amazon RDS MySQL vs Amazon DynamoDB for querying a table with 1 million items, the differences in costs depends on factors like query complexity, read patterns, and indexing.

Here is a brief but detailed breakdown.

Amazon RDS MySQL Costs

• Instance Costs: RDS is billed based on the instance size and storage. A typical db.t3.medium costs $0.0416/hour ($30/month if running 24/7).

• Storage Costs: $0.115 per GB/month (10 GB = $1.15/month).

• IO Costs (if using IOPS-based storage): $0.10 per million I/O requests.

• Query Costs: There is no direct cost per query, but queries consume CPU, memory, and disk IO.

Total Estimate:

• If running an on-demand RDS instance 24/7: ~$31/month 

• If using Aurora Serverless: Starts at ~$4/month (but scales based on usage).

Amazon DynamoDB Costs

Read Costs:

• On-Demand Mode: $1.25 per million reads.

• Provisioned Mode: ~$0.00013 per read request (strongly consistent).

• Storage Costs: $0.25 per GB/month.

• Indexes: GSI costs extra ($0.25 per GB + read/write ops).

Query Costs:

• Queries typically cost 1 read per 4KB item, so fetching a 1KB item costs 1 read.

• Scanning the entire table would cost 1 million reads = $1.25 (on-demand).

Cost Comparison Summary

The Takeaways:

• If you query a few times per second, DynamoDB is cheaper.

• If you run complex queries on large datasets, RDS may be more cost-effective.

• For full table scans, RDS doesn’t charge per query, while DynamoDB can get expensive fast.

Which One Should You Use?

Use DynamoDB if:

• You need low-latency, high-scale queries.

• You mainly do single-item lookups or indexed range queries.

• You don’t want to manage servers.

• Your access patterns are predictable.

Use RDS if:

• You need complex filtering, aggregations, and joins.

• Your queries often involve ad-hoc conditions.

• You want to avoid DynamoDB’s per-query costs for large scans.

• Your dataset doesn’t grow exponentially.

One Tip To Save Costs

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Curated Article

1. “5 Strategies I Use To Save Big On Costs With DynamoDB”. Uriel Bitton. https://medium.com/towards-aws/5-strategies-i-use-to-save-big-on-costs-with-dynamodb-94f976e5d090

2. “How Samsung Cloud Uses DynamoDB To Optimize Costs”. Uriel Bitton. https://aws.plainenglish.io/how-samsung-cloud-uses-dynamodb-to-optimize-costs-a058e4033112