Amazon DynamoDB
maang.io System Design Series
DynamoDB is AWS's fully-managed, serverless database from the Dynamo lineage — the same distribution ideas as Cassandra, but operated for you. Master its partition/sort keys, GSIs vs LSIs, capacity modes, tunable consistency, and query-first single-table design, and you can reason about planet-scale key-value systems and defend when to reach for it over a self-managed cluster.
This deep dive comes in four parts:
- Foundations & Core Concepts — the data model, keys, and partitions.
- Internals — capacity (RCU/WCU), adaptive capacity, indexes, and consistency, with worked numbers.
- Advanced Internals — Streams, TTL, and single-table design patterns.
- Interview — Staff/Principal Q&A: modeling, hot partitions, and DynamoDB vs Cassandra.
Amazon DynamoDB — Part 3: Reads, Capacity & Indexes
maang.io System Design Series
What is this?
Part 2 took a write from the front desk to durable storage. This chapter follows a read back out, then covers the four things a Staff engineer must actually reason about in a design review: how much a read or write costs (RCU/WCU), how you pay for it (provisioned vs on-demand, and how DynamoDB absorbs spikes), how to query by something other than your primary key (GSIs vs LSIs — the single most-asked DynamoDB interview question), and the change-capture and expiry tools (Streams, TTL, transactions).
Same warehouse: now we care about how fast the concierge can fetch a box, how many robots you rented, and the extra card-catalogs you set up to find boxes by something other than their label.
The one-line idea: Every DynamoDB knob is a cost-vs-guarantee trade: eventual reads are half the price of strong ones; on-demand trades a small premium for zero planning; a GSI buys a new query pattern at the cost of extra storage, extra writes, and eventual consistency; and adaptive capacity papers over moderate skew but never rescues a single scorching-hot key.
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