[bitcoin-dev] The increase of max block size should be determined by block height instead of block time

Jeff Garzik jgarzik at gmail.com
Fri Dec 18 20:15:54 UTC 2015

My preference is height activation + one step per block (i.e. also
height).  Height seems KISS.

AFAICT most of the attacks would occur around the already-heavily-watched
flag day activation event, in a height based environment, a useful

However I would like to hear from others about possible attacks with the
various approaches, before diverging from the default community approach of

On Fri, Dec 18, 2015 at 3:10 PM, Jorge Timón <jtimon at jtimon.cc> wrote:

> Well, if it's not going to be height, I think median time of the previous
> block is better than the time of the current one, and would also solve Chun
> Wang's concerns.
> But as said I prefer to use heights that correspond to diff recalculation
> (because that's the window that bip9 will use for the later 95%
> confirmation anyway).
> On Dec 18, 2015 9:02 PM, "Jeff Garzik" <jgarzik at gmail.com> wrote:
>> From a code standpoint, based off height is easy.
>> My first internal version triggered on block 406,800 (~May 5), and each
>> block increased by 20 bytes thereafter.
>> It was changed to time, because time was the standard used in years past
>> for other changes; MTP flag day is more stable than block height.
>> It is preferred to have a single flag trigger (height or time), rather
>> than the more complex trigger-on-time, increment-on-height, but any
>> combination of those will work.
>> Easy to change code back to height-based...
>> On Fri, Dec 18, 2015 at 2:52 PM, Jorge Timón <
>> bitcoin-dev at lists.linuxfoundation.org> wrote:
>>> I agree that nHeight is the simplest option and is my preference.
>>> Another option is to use the median time from the previous block (thus
>>> you know whether or not the next block should start the miner confirmation
>>> or not). In fact, if we're going to use bip9  for 95% miner upgrade
>>> confirmation, it would be nice to always pick a difficulty retarget block
>>> (ie block.nHeight % DifficultyAdjustmentInterval == 0).
>>> Actually I would always have an initial height in bip9, for softforks
>>> too.
>>> I would also use the sign bit as the "hardfork bit" that gets activated
>>> for the next diff interval after 95% is reached and a hardfork becomes
>>> active (that way even SPV nodes will notice when a softfork  or hardfork
>>> happens and also be able to tell which one is it).
>>> I should update bip99 with all this. And if the 2 mb bump is
>>> uncontroversial, maybe I can add that to the timewarp fix and th recovery
>>> of the other 2 bits in block.nVersion (given that bip102 doesn't seem to
>>> follow bip99's recommendations and doesn't want to give 6 full months as
>>> the pre activation grace period).
>>> On Dec 18, 2015 8:17 PM, "Chun Wang via bitcoin-dev" <
>>> bitcoin-dev at lists.linuxfoundation.org> wrote:
>>>> In many BIPs we have seen, include the latest BIP202, it is the block
>>>> time that determine the max block size. From from pool's point of
>>>> view, it cannot issue a job with a fixed ntime due to the existence of
>>>> ntime roll. It is hard to issue a job with the max block size unknown.
>>>> For developers, it is also easier to implement if max block size is a
>>>> function of block height instead of time. Block height is also much
>>>> more simple and elegant than time.
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