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

From: Jeff Garzik <jgarzik@gmail•com>
To: "Jorge Timón" <jtimon@jtimon•cc>
Cc: Bitcoin Dev <bitcoin-dev@lists•linuxfoundation.org>
Subject: Re: [bitcoin-dev] The increase of max block size should be determined by block height instead of block time
Date: Fri, 18 Dec 2015 15:15:54 -0500	[thread overview]
Message-ID: <CADm_Wcah3V7yxCpt97rK89_0GY8HZm6xbCg0yqjKRWak7crt5Q@mail.gmail.com> (raw)
In-Reply-To: <CABm2gDoyzLErwA0g624A2aPUqSi3gXTgcmC7TTTUNDKyecDpuA@mail.gmail.com>

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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
attribute.

However I would like to hear from others about possible attacks with the
various approaches, before diverging from the default community approach of
switch-based-on-time.

On Fri, Dec 18, 2015 at 3:10 PM, Jorge Timón <jtimon@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@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@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@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.
>>>> _______________________________________________
>>>> bitcoin-dev mailing list
>>>> bitcoin-dev@lists•linuxfoundation.org
>>>> https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev
>>>>
>>>
>>> _______________________________________________
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>>>
>>

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