Disabling min-difficulty blocks on testnet4

The Problem Testnet4 has encountered significant issues due to its 20-minute min-difficulty rule, which was initially introduced to facilitate easier mining on the test network. This rule permits the mining of a block at the lowest difficulty level if no blocks have been mined in the past 20 minutes. However, this well-intentioned feature has led to unintended consequences, notably the proliferation of CPU miners who exploit this loophole to mine blocks at minimal difficulty. The fierce competition among miners to quickly broadcast these min-difficulty blocks has resulted in many opting to send empty blocks, thereby gaining slight advantages in terms of bandwidth and verification time. This strategy, while effective for individual miners, undermines the test network's primary function by significantly reducing the number of transactions confirmed per block.

In response to these challenges, a proposal has been put forward to disable the min-difficulty rule on Testnet4. This would be achieved through a hard fork scheduled at block height 201,600, coinciding with the epoch 100 boundary. This timing aligns neatly with the 2016-block difficulty adjustment interval and allows node operators adequate time to prepare for the upgrade. The proposed changes are anticipated to take effect between August and September of 2027, eliminating the 20-minute min-difficulty exception and enforcing standard difficulty rules through the GetNextWorkRequired() and PermittedDifficultyTransition() functions. Notably, the proposal opts against resetting the difficulty level to an arbitrary value at the fork, instead relying on standard retargeting mechanisms to facilitate a natural transition.

Several key points of discussion accompany this proposal. There is ongoing debate regarding the optimal block height for implementing the fork, with height 201,600 identified as a preliminary choice subject to further deliberation. Moreover, the question of whether these modifications necessitate the creation of a Bitcoin Improvement Proposal (BIP) has been raised, given the impact on Testnet4's consensus rules. Additionally, there are concerns about the potential for approximately one-hour block intervals during the period of difficulty normalization following the fork.

For further details on this proposal, interested parties can refer to the pull request on GitHub (PR), discussions on the Bitcoin developers' mailing list (Mailing list discussion), and the Bitcointalk forum thread (Bitcointalk). These resources provide comprehensive insights into the motivations behind the proposed changes and the broader community's perspectives on the issue.