EVM vs. SVM: Consensus
Learn the differences in how Ethereum and Solana achieve consensus.
Both Ethereum and Solana are known to use PoS (Proof of Stake) for their consensus mechanisms. They both generate blocks through validators based on staking. Although they fundamentally use the same consensus, Ethereum currently records about 30 TPS (transactions per second), while Solana boasts 4000 TPS. This difference indirectly shows how consensus can significantly impact block generation speed. This chapter will delve into the differences between the two chains.
Ethereum's original consensus
Originally, Ethereum adopted the Proof of Work(PoW) method, which is still used by Bitcoin. After the Merge upgrade in August 2022, Ethereum transitioned from Proof of Work to Proof of Stake, and now employs PoS as mentioned above.
Ethereum's current consensus
At its core, Ethereum uses PoS, but it specifically employs a consensus algorithm called Gasper. Gasper is a combination of Casper the Friendly Finality Gadget (Casper-FFG) and the LMD-GHOST fork choice algorithm. Before delving into Gasper, it's important to note that Ethereum initially generates blocks based on the PoW-based Nakamoto consensus. The Nakamoto consensus follows the Longest Chain Rule, selecting the longest chain in the blockchain during a fork. Therefore, Ethereum hasn't completely abandoned PoW; it retains basic block generation under PoW while integrating PoS elements on top.
Casper (Casper-FFG), a part of Gasper, upgrades certain blocks to a "finalized" state, ensuring network participants are synchronized with the regular chain. It was initially proposed for the transitional phase from a PoW-based chain to PoS during the Merge upgrade and now contributes partially to the larger Gasper algorithm. LMD-GHOST (Latest Message Driven Greediest Heaviest Observed SubTree) is a fork choice algorithm used to select the most valid and trustworthy chain among various forks. In case of a fork generating multiple new blocks, validators vote through attestation messages to determine which block to append to the existing chain. These attestations follow a path from the genesis block to the latest block (leaf block), selecting the block backed by the most recent attestations.
Solana's consensus
What are the corresponding technological components in Solana for each of Ethereum's consensus algorithms? The answer lies in Tower BFT, which supports PoS.
First, let's understand BFT and PBFT. BFT is a method for achieving reliable consensus among nodes in a distributed system, stemming from the 'Byzantine Generals Problem.' It ensures the system operates correctly even if some nodes are malicious or unreliable. PBFT is a practical implementation of BFT that guarantees system finality and consistency by securing agreement on all transactions among all nodes.
Tower BFT adopts a variant of PBFT, with one fundamental difference: Proof of History (PoH) acts as a global clock before consensus. In Solana's implementation, PoH is used as the network clock, arranging the order of blocks, transactions, and data.
Ethereum often inefficiently updates its entire network state for specific transactions, and transactions may not be processed sequentially. In contrast, Solana utilizes PoH (Proof of History) to support PoS. To determine the cryptographic time between two events, a series of computational steps are required. For example, consider two photos: one of an apple and another of the photo being taken. We can infer that the photo of the apple was taken first. Solana tracks their sequence by adding timestamps to data, ensuring no mix-up in its structures.
Using PoH, Tower BFT effectively determines the order of blocks, transactions, and data through timestamp verification. Therefore, validators can conclusively decide on forks, opting for the chain most trusted by votes. Ethereum lacks a timestamp concept like PoH for overall state synchronization, forcing validators to calculate from previous hashes to select a fork. Conversely, Solana's Tower BFT, based on PoH, effortlessly achieves consensus without needing full block verification.
Therefore, the comparison can be summarized as follows:
| Ethereum | Solana |
| Proof of Work » Proof of Stake | Proof of Stake> |
| Casper the Friendly Finality Gadget (Casper-FFG) | Tower BFT + PoH |
| LMD-GHOST Fork Choice Rule | Tower BFT |
Summary
- Ethereum’s Consensus: PoS based Gasper = Casper the Friendly Finality Gadget (Casper-FFG) + LMD-GHOST Fork Choice Rule
- Solana’s Consensus: PoS based Tower BFT + PoH
