About DynamoDB Query Simulator

Simulate DynamoDB scan and query operations with expressions. Part of the DevTools Surf developer suite. Browse more tools in the Database Tools collection.

Use Cases

• Design DynamoDB query patterns before building the application data model
• Test scan vs query performance trade-offs for access patterns
• Understand how to use the sort key for range queries and filtering
• Prototype Global Secondary Index (GSI) queries without deploying infrastructure

Tips

• Define your table's partition key and sort key before building queries — DynamoDB's access patterns are determined by key design, not query flexibility like SQL
• Use the FilterExpression vs KeyConditionExpression distinction — filter expressions apply after reading all matching partition items; key conditions limit which items are read
• The consumed capacity display shows how many read capacity units (RCUs) each simulated query consumes — optimize by reducing scan width and using projections

Fun Facts

• Amazon DynamoDB was launched in 2012, based on lessons from Amazon's internal Dynamo paper published in 2007. The original Dynamo paper described a highly available key-value store that sacrificed consistency for availability — an influential design that spawned multiple NoSQL databases.
• DynamoDB stores data across multiple partitions automatically. A partition can handle 3,000 RCUs and 1,000 WCUs and stores up to 10GB. Tables with millions of items and hot partitions can exhaust per-partition limits even when total table capacity is unused — requiring careful key design to distribute load.
• DynamoDB's on-demand pricing mode, launched in 2018, charges per-request rather than for provisioned capacity. This made DynamoDB cost-effective for unpredictable or spiky workloads where provisioned capacity was often wasted — a significant shift in serverless architecture economics.

FAQ

When should I use DynamoDB vs PostgreSQL?

DynamoDB excels at high-throughput key-value and document access at any scale with predictable single-digit millisecond latency. PostgreSQL is better when you need complex queries, joins, ad-hoc analysis, or ACID transactions across multiple entities. DynamoDB requires knowing all access patterns upfront.

What is a hot partition in DynamoDB?

A hot partition occurs when too many requests target the same partition key, exceeding the per-partition limits (3,000 RCUs, 1,000 WCUs). Common causes: sequential keys (dates, incremental IDs), celebrity items. Solutions: add a random suffix (sharding), use write sharding patterns.

What is the difference between Scan and Query in DynamoDB?

Query reads items with a specific partition key (optionally filtering by sort key) — efficient and targeted. Scan reads every item in the table (or index) and optionally filters — expensive and should be avoided in production for large tables.