An article introducing the history of the "difficulty bomb" and Ethereum Arrow Glacier upgrade

What changes will the Arrow Glacier upgrade bring?

Arrow Glacier is the third network upgrade of the Ethereum network’s proof-of-work blockchain scheduled for 2021. Earlier this year, the Ethereum mainnet successfully deployed the Berlin upgrade in April and the London upgrade in August, which deployed 4 EIPs and 5 EIPs respectively.

Arrow Glacier is tentatively scheduled to be completed on December 8, 2021.

What changes will the Arrow Glacier upgrade bring?

Arrow Glacier is another network upgrade similar to Muir Glacier. This will consist of only one improvement proposal to push the difficulty bomb until next summer to ensure that the chain does not freeze, aka an “ice age.”

EIP-4345: Difficulty Bomb Delayed to June 2022

The EIP proposal postpones the defusing of the bomb in London by a total of 10.7 million blocks, which is 1 million more than the last time London was postponed. This nuclear bomb may appear in June 2022.

On October 5, Tim Beiko initially proposed an EIP that would push the bomb to 10.5 million blocks, until May 2022. However, in further discussion at AllCoreDevs, it was decided to move the bomb to next summer.

The core developers’ reasonable confidence in getting a merged upgrade by next summer is undoubtedly a consideration. Beyond that, Thomas Jay Rush’s article Adventures in Difficulty Bombing provides a better reason for how far the bomb should be set and helps justify delaying its removal from the initial plan. Ethereum client teams want to avoid organizing another boycott when the next major upgrade is made.

History of the Difficulty Bomb

The difficulty bomb is a set of code added to the Ethereum blockchain to exponentially increase the difficulty level, making it difficult for miners to keep up. Block times will increase and will cause the blockchain to freeze. It's a very "steep" exponential curve; it's flat for a long time, and then when the bomb "explodes" it quickly kicks into gear.

Why add the difficulty bomb in the first place?

The difficulty adjustment process was originally designed to facilitate the transition to Proof of Stake. Over time, it acquired the additional property of forcing those who wish to continue running Ethereum to upgrade their nodes. This means that staying on the old chain is not an option.

Timeline and related EIPs

November 2015: EIP-2: Homestead Hard-fork Changes made changes to the pre-homestead difficulty adjustment algorithm.

April 2016: EIP-100: Changed the difficulty adjustment to target the average block time, including uncle blocks, and updated the difficulty adjustment algorithm to target a constant average block generation rate, including uncle blocks, thereby ensuring a highly predictable issuance rate that cannot be increased by manipulating the uncle block rate.

June 2016: EIP-649: Metropolis Difficulty Bomb Delay and Block Reward Reduction, delaying the difficulty bomb by about a year and a half and reducing block rewards using the Byzantium fork, the first part of the Metropolis fork.

July 2018: EIP-1234: Constantinople Difficulty Bomb Delay and Block Reward Adjustment delayed the difficulty bomb by approximately 12 months and reduced block rewards via the Constantinople fork (the second part of the Metropolis fork).

November 2019: EIP-2384: Muir Glacier Difficulty Bomb Delay, postpones the difficulty bomb to the next 4,000,000 blocks (~611 days).

May 2021: EIP-3554: Difficulty Bomb Delayed to December 2021, this EIP was deployed in August along with the London upgrade to delay the difficulty bomb so that it would show effects in the first week of December 2021.

October 2021: EIP-4345: Difficulty Bomb Delayed to June 2022 This EIP pushes the difficulty bomb to 10,700,000 blocks later than the actual block number. Most likely, it will be activated on the Ethereum mainnet on December 8, 2021.

What do I need to do?

If you are running any number of Ethereum PoW nodes, it is strongly recommended that you upgrade your nodes with the latest client version before the Arrow Glacier upgrade activation date. Please stay tuned to the Ethereum Foundation's announcement blog for more information.

Source: https://medium.com/ethereum-cat-herders/ethereum-arrow-glacier-upgrade-e8d20fa4c002