Event Sourcing vs. Blockchain: Where Immutability Matters

"Immutability isn’t magic—it’s a tradeoff."

Both event sourcing and blockchain promise:
🔒 Data that can’t be deleted
⏳ Full history tracking
🔍 Transparent auditing

But they solve very different problems. Use the wrong one, and you’ll pay—in complexity, performance, or coffee-fueled all-nighters.

Here’s how to choose.

1. Core Philosophies

Event Sourcing

• What it is:
  • Append-only log of domain events (e.g., OrderPlaced, UserBanned)
  • Projections rebuild current state
• Where it shines:
  • Debugging ("Why is this user’s balance $0?")
  • Temporal queries ("Show me yesterday’s dashboard")
  • Undo/redo workflows

Blockchain

• What it is:
  • Decentralized ledger of transactions
  • Consensus-driven (no single owner)
• Where it shines:
  • Distrustful environments (e.g., crypto, supply chains)
  • Provenance tracking (e.g., NFT ownership)
  • Censorship resistance

2. Key Differences

3. When to Use Event Sourcing

Ideal Scenarios

✅ Audit-heavy domains (banking, healthcare)
✅ Complex workflows (e.g., order cancellations)
✅ Debugging production issues

Example

# Replay to debug a pricing bug
events = EventStore.for(order_id).up_to("2023-05-10")
PricingCalculator.replay(events) # Find where math broke

4. When to Use Blockchain

Ideal Scenarios

✅ Distrustful parties (e.g., supplier tracking)
✅ Asset ownership (e.g., deeds, IP rights)
✅ Censorship resistance (e.g., activist archives)

Example

// NFT ownership on Ethereum
function transfer(address to, uint256 tokenId) public {
  require(ownerOf(tokenId) == msg.sender);
  _transfer(msg.sender, to, tokenId); // Immutable record
}

5. The Hybrid Approach

Case Study: Supply Chain

• Blockchain:
  • Record cross-company transactions (e.g., "Shipment left factory")
• Event Sourcing:
  • Power internal logistics (e.g., warehouse routing)

Implementation

# When shipment departs
event = ShipmentDispatched.new(tracking_id: "123")
EventStore.publish(event)
Blockchain.record(event) # Write to Hyperledger

6. Pitfalls to Avoid

🚫 Using blockchain as a database:

• 10K RPM writes will kill your wallet (and sanity) 🚫 Ignoring privacy in event sourcing:
• GDPR requests become nightmares without redaction 🚫 Overengineering:
• Not every app needs provable immutability

"But Our CTO Loves Blockchain!"

Ask:

1. Do we need decentralization? (If not, event sourcing is cheaper)
2. Who’s paying for gas fees? (Spoiler: Your ops team will revolt)
3. Can we fake it? (A cryptographically signed event store often suffices)

Have you used either (or both)? Share your war stories below.