AdvancedSystem-Design
45 min
Design a Blockchain Ledger System
BlockchainConsensusDatabasesSecurity
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Interview Question
Design a blockchain ledger for financial transactions with consensus, immutability, and efficient query capabilities.
Key Points to Cover
- Consensus: PoW, PoS, Raft/BFT trade-offs
- Block structure, Merkle trees, immutability guarantees
- Smart contract execution model and gas/fees
- Querying chain state efficiently; indexes and snapshots
- Security considerations: Sybil attacks, double spend, forks
Evaluation Rubric
Correct consensus model trade-offs25% weight
Sound ledger structure & immutability25% weight
Efficient chain state/query design25% weight
Security threat model handling25% weight
Hints
- 💡Use append-only logs and snapshots for fast queries.
Common Pitfalls to Avoid
- ⚠️Over-reliance on a single consensus mechanism without considering trade-offs for specific use cases.
- ⚠️Underestimating the complexity of integrating efficient query capabilities with blockchain immutability.
- ⚠️Neglecting the 'oracle problem' – securely bringing external data onto the blockchain for smart contracts.
- ⚠️Insufficient gas/fee mechanism design leading to economic instability or network congestion.
- ⚠️Lack of robust security auditing and ongoing vulnerability management for smart contracts and the network infrastructure.
Potential Follow-up Questions
- ❓How do you prevent forks?
- ❓How would you prune/archive historical data?
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