This is Post 4 in the Blockchain Series. The previous post covered DeFi protocol design.

Why Layer 2 Exists

Base layers optimize decentralization and security, but throughput is limited. Layer 2 systems move execution off-chain while inheriting L1 settlement.

Rollup Types

  • Optimistic rollups: assume valid by default; fraud proofs during challenge windows.
  • ZK rollups: validity proofs (SNARK/STARK) submitted to L1.

Data Availability (DA)

State validity is not enough; users need transaction data to reconstruct state.

DA approaches:

  • Post calldata/data blobs on Ethereum.
  • Validium/volition (trade-offs in DA trust).
  • Modular DA layers for high throughput.

Choosing the Right Architecture

  • Need fastest finality and high security assumptions? → ZK rollup.
  • Need EVM compatibility with mature tooling? → Often optimistic first.
  • Need lowest costs for consumer apps? → Hybrid with strong DA guarantees.

References

  • Ethereum rollup-centric roadmap notes: https://ethereum-magicians.org/
  • OP Stack docs: https://docs.optimism.io/
  • zkSync docs: https://docs.zksync.io/
  • Arbitrum docs: https://docs.arbitrum.io/

Best Books

  • Alex Xu, System Design Interview (scalability mindset, complementary).
  • Narayanan et al., Bitcoin and Cryptocurrency Technologies.
  • Andreas M. Antonopoulos & Gavin Wood, Mastering Ethereum.

Updated:

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