28 Jun 2024

Parallel EVM: Sei-v2

This is a personal note for Sei-v2-blog as well as some terminology explained by EVM GPT.

1. Blockchain fundamentals

Mainnet: real transactions occur and have real-world value; any operation is final and irreversible.
Testnet: a sandbox environment with test cryptocurrencies without real-world value.

Alpha: test core functionalities and gather initial feedback in live environment.
Beta: more stable and feature-complete, but still need more testing.

L1: the main network where all transactions are processed and the primary chain is maintained.
L2: secondary frameworks on top of L1 chain, aimed to enhance scalability without compromising the security of the L1.

Processes transactions off-chain and periodically submits a summary (rollup) to L1.
Optimistic rollups: assume transactions are valid be default and use a challenge period to allow disputes
- Examples: Optimism, Arbitrum.
ZK-rollups: use zero-knowledge proofs to validate transactions.
- Examples: zkSync, StarkNet.

allow participants to conduct numerous off-chain transactions, with only the final state recorded on the L1.
Examples: Bitcoin lightning network.

Independent blockchains running parallel to the main chain, with own consensus and security.
Examples: Polygon.

Ethereum: a blockchain ecosystem, includes the blockchain, consensus mechanism, smart contracts, native cryptocurrency.
EVM: the runtime environment to execute smart contracts in Ethereum.

AVL tree: self-balancing binary tree where the difference in heights between left and right subtrees of anynode is at most one.
IAVL tree: immutable AVL tree; node cannot be changed once it is added.

Allows developers to write fast and portable smart contracts in WebAssembly.
Designed to be interoperable within in the Cosmos ecosystem, a network of independent blockchains connected via the Inter-blockchain communication (IBC) protocol.

A network of independent, interoperable blockchains designed to create an Internet of blockchain.
Decouples the consensus (BFT consensus engine) and networking (IBC protocol) layers from the application layers
Cosmos SDK: a modular framework for building application-specific blockchains efficiently.
Cosmos Hub: the first blockchain in the Cosmos network, serves as a central hub to connect multiple blockchains via IBC.

Infrastructure layer: the physical devices that support the network; and the underlying communication protocols for data transfer between nodes.
Data layer: the distributed ledger and the storage methods.
Consensus layer: the protocols, validators and miners; determines the transaction orders.
Execution layer: smart contracts and virtual machines; determines the transaction update.
Application layer: dApps to provide service and user interfaces.
Governance layer: the community decision-making process and proposals.
Security layer: cryptographic primitives and security protocols to avoid attacks.

Multiple transactions are processed in parallel under the assumption that they will conflict with each other; necessary corrections are made afterwards if conflicts are detected.
Increase throughput if conflicts are well handled.

Integrated: all components, e.g., execution layer, consensus mechanism, networking are tightly coupled; faster internal communication but lower flexibility and scalability.
Modular: allow independent upgrades for different components; enhance scalability.

Execution: responsible for running smart contracts and processing transactions.
Storage: store all blockchain data, e.g., accounts, smart contract states, transaction history.

Block: the average time for a new block to be added.
Finalize: the period after which a block is considered irreversible.
Faster block times often imply cheaper transaction fees due to increased transaction throughput and less block competition.

On mainnet beta since August 2023.
Consistently finalizes blocks at 390ms; the fastest chain in existence.
Consistently sees activity of >45 TPS (transaction per seconds); the second highest number of successful transactions per second.
Allows for Cosmwasm smart contracts written in Rust; more execution environments like EVM is the biggest request.

The first fully parallelized EVM.
Backwards compatibility of EVM smart contracts.
Optimistic parallelization; support parallelization without requiring any dependencies.
Improves the storage layer to prevent state bloat, read/write, and state sync for new nodes.
Seamless composability between different execution environments.
Offers 28,300 batched transactions per second of throughput; 390ms block times and 390ms finality; far cheaper per-transaction costs.
Once audits are complete, the upgrade is released in a public testnet in Q1 2024, and deployed to mainnet in H1 2024.

Ethereum contracts can be seamlessly deployed on Sei v2 with no code changes.
User can send a Eth transaction to the Ethereum contract on Sei v2 via the same interface, e.g., Metamask, Hardhat.
Sei v2 imports Geth (a Go EVM implementation) to process the Eth transaction, and convert the result to Sei storage.

Sei requires smart contract developers to optionally define the state that smart contracts are using, Sei v2 removes this need.
Sei v2 chain optimistically runs all transactions in parallel, when reaching conflicts, i.e., transactions touching the same state, the chain tracks the storage parts each transaction is touching.
Transactions touching different parts will be rerun in parallel; transactions touching the same state will be rerun sequentially.
Recursively continue until no more conflicts.
Since the transactions are ordered in a block, this process is deterministic.

Sei uses a vanilla database layer composed of an IAVL tree, which is less efficient in terms of storage and latency.
Sei v2 breaks the single IAVL tree into 2 components:
- state store: provide low latency direct access to raw key-value pairs to remove the overhead of redundant metadata and disk usage; uses a write-ahead log to help event recovery.
- state commitment: use an in-memory IAVL tree to help validators reach consensus faster.
After benchmarking, Sei v2 replaces GoLevelDB with PebbleDB for better read/write in multi-threaded access.

Sei v2 processes different transactions, e.g., Cosmwasm, EVM in a uniformed way, and then forwards them to different storage sections.