Blockchain technology plays a crucial role in various industries globally, particularly in finance and data management. One such innovation in the blockchain space is the LMD-GHOST (latest-message-driven Greedy Heaviest Observed Subtree) fork choice rule. Terence Chain of the Prysm Ethereum Client recently emphasized the importance of blockchain liveness and the LMD-GHOST fork choice rule in a tweet on May 12, 2023. This came after an incident on May 11 involving Ethereum, the second-largest blockchain in terms of market capitalization.
On May 11, the Ethereum blockchain encountered a technical problem that led to a disruption where blocks were not being finalized for over an hour. This marked the second outage of this nature in the last 24 hours. Terence Chain observed that even though Ethereum did not finalize for three epochs during the incident, the blockchain continued to operate smoothly without any noticeable hiccups for users. He attributed this to the LMD-GHOST fork choice rule, which prioritizes liveness over strong safety.
Chain added in his tweet that those affected by the incident were mainly those who relied on the finalization of the chain, such as users waiting for L1 to L2 deposits to complete. He concluded by stating that if strong safety had been prioritized over liveness, the chain would have halted, and the user experience would have been far worse.
The outage raised significant security concerns for users of the Ethereum platform. The Ethereum Foundation stated that during periods when blocks are not being finalized, there is a potential risk of pending transactions being re-ordered or even dropped from the network. Terence Chain later reported on May 13 that the network had resumed finalizing blocks, but this was the second time within a 24-hour period that Ethereum’s performance had been affected. The same issue occurred the previous day when finality was paused for approximately 25 minutes.
LMD-GHOST is a fork choice rule that helps resolve conflicts in the blockchain when multiple blocks are proposed simultaneously. It allows validators to choose the “heaviest” subtree, which refers to the subtree containing the most recent block messages from validators. The heaviest subtree is considered the canonical chain, and all other subtrees are deemed to be forks. By utilizing this rule, the Ethereum blockchain is ensured to have a high level of liveness, meaning that it can continue to accept and process new transactions even when there is a lack of finality.
Liveness is an essential characteristic of blockchain systems as it ensures that the network remains functional even during times of uncertainty or potential attacks. It makes certain that users can continue to interact with the system and that their transactions are not halted indefinitely. On the other hand, strong safety prioritizes the security and integrity of the network by focusing on protecting against attacks, such as double-spending or chain reorganizations, which can potentially compromise the system’s security.
In the case of the Ethereum incident, the LMD-GHOST fork choice rule’s prioritization of liveness allowed the network to continue operating without much disruption, even when finality was not achieved for some time. This highlights the importance of liveness in blockchain systems and the need for a balance between safety and continued functionality.
Overall, Terence Chain’s emphasis on the LMD-GHOST fork choice rule and blockchain liveness offers valuable insight into the workings of the Ethereum blockchain and the importance of maintaining a balance between safety and functionality in blockchain systems. Blockchain developers and users alike must continue to prioritize both safety and liveness in the design and adoption of blockchain technologies to ensure that they remain efficient, secure, and functional even during times of uncertainty or network disruptions.