bip9 model bits – Ought to block top or MTP or a mix of each be utilized in a comfortable fork activation mechanism?
Ought to block top or MTP (median time previous […]) or a mix of each be utilized in an activation mechanism like BIP 8 or BIP 9 for outlining the timings of the state transitions? What are the benefits and drawbacks of each and the way do they evaluate?
The primary benefit of MTP is that it often roughly corresponds to wall time, so it is easy to speak what a quantity means to people. For instance, BIP141 says: “the BIP9 starttime can be midnight 15 november 2016 UTC […] and BIP9 timeout can be midnight 15 november 2017 UTC”. When each of these MTP values have been reached on the precise community, they have been inside three hours of precise UTC.
The primary drawback of MTP is that it may be manipulated by miners. MTP is the median of the worth recorded within the nTime discipline of the present block header and the earlier 10 blocks. Miners can set their nTime values to any worth higher than the present MTP and fewer than two hours sooner or later. This makes it potential for a majority of miners working for an prolonged period of time to carry MTP to an previous worth (say 3 months in the past) after which, within the house of a single block, transfer to a a lot later time (say 1 month in the past). This could enable them to leap over MTP-based necessary signaling durations comparable to laid out in BIP148.
The primary benefit of block heights is that there is not any solution to skip over a height-based threshold, in order that they make sense for flag day activations, necessary signaling necessities, and different transitions we need to guarantee occur (comparable to from BIP9 LOCKED_IN to ACTIVE, which occurs utilizing a relative height-based threshold of two,016 blocks).
The primary drawback of block heights is that they are not significantly constant. In a mean yr, we count on there to be 52,596 blocks, however it could not be extraordinary for there to be 58,440 blocks—reducing an supposed 12-month deployment to 10.8 months.
There isn’t any hurt in mixing MTP instances and heights, and there might be important benefits when you can make the most of each strengths on the similar time with out dropping an excessive amount of to their weaknesses.