Write-Ahead Message

Cloud-native pattern using S3-like storage, inspired by WAL. Traditional solutions work but are costly; WAM provides reliability at a fraction of the cost.

What is WAM?

Write-Ahead Message (WAM) is a pattern that ensures messages are written durably to cloud storage like S3 before acknowledgment. The core principle is "Write message first, acknowledge later".

WAM is inspired by the WAL (Write-Ahead Log) pattern from databases, but adapted for message-oriented systems. The key distinction: WAM is about messages, not logs.

The Concept

graph LR A[Client] -->|sends message| B[API] B -->|write to| C[Cloud Storage
S3-like] C -->|durable| D[ACK to Client] C -->|async| E[Cache Layer]
  • Message written to cloud storage (S3-like) synchronously
  • ACK sent only after durable write completes
  • Cache updated asynchronously for fast reads

Why WAM?

  • Cost-effective: Cloud storage (S3) is much cheaper than traditional databases at scale
  • Cloud-native: Built for modern cloud infrastructure, leveraging object storage
  • Reliable: Messages survive crashes and can be replayed to restore state

WAM vs WAL

Similarities: Both use append-only pattern and ensure durability before acknowledgment.

Difference: WAL handles database transactions, while WAM handles messages in chat platforms.

Conclusion

WAM brings reliable, cost-effective message durability to chat platforms using cloud-native storage. It adapts the proven WAL pattern from databases to the unique needs of message-oriented systems.