Coupang Engineering: Replacing Database Sequences with DynamoDB-Based Distributed Counter Service

Coupang's engineering team has shared a detailed account of building a distributed sequence service using DynamoDB and dual-layer caching to replace over 10,000 database sequences across 100+ services during a migration from relational databases to NoSQL.

The Challenge

• Over 100 teams depended on native database sequences for primary keys
• Some teams required sequences for sorting, others for downstream system compatibility
• Nearly 10,000 different counters across the organization
• DynamoDB doesn't support native sequences
• UUIDs would break existing sorting logic
• Snowflake IDs would introduce unwanted operational complexity

Requirements

• Unique and monotonically increasing values
• High availability (Tier-0 service)
• Low latency (sub-millisecond on hot path)
• Zero network calls on hot path (local cache generation)
• Backward compatible (start values, custom steps, ascending/descending)
• Zero-downtime migration capability

Architecture: Three-Layer Caching

Client Local Cache -> Server Cache Layer -> DynamoDB (source of truth)

• Client cache: Generates sequences locally without any network roundtrip
• Server cache: Pre-fetches 500-1000 values per batch
• DynamoDB: Atomic conditional updates using SET val = val + blockSize WHERE val = expectedValue
• Result: Less than 0.1% of requests reach DynamoDB

Key Design Decisions

1. Accept gaps: Unused sequences lost on server crash is acceptable
2. Batch fetching: One DynamoDB write supports hundreds of cache-level requests
3. No distributed locks: Conditional updates provide conflict-free uniqueness
4. Simplicity over sophistication: Avoided consensus protocols, vector clocks, distributed locks

Results

• Order team migrated 12 services in 3 weeks with zero downtime
• Less than 50 lines of code changed per service
• Sub-millisecond latency for cached sequence generation
• Complete backward compatibility with original database sequences

Design Philosophy

"Complex systems fail in complex ways. Every layer of coordination adds latency, more failure modes, and heavier operational burden." -- Coupang Engineering

This case study is a valuable reference for any organization migrating from relational databases to NoSQL and dealing with the sequence/ID generation challenge at scale.