[bitcoin-dev] Segregated Witness in the context of Scaling Bitcoin

Dave Scotese dscotese at litmocracy.com
Sat Dec 19 23:03:20 UTC 2015


A couple observations:

   - The consensus block limit is different than the disk space required to
   do validation.  Some participants are worried about one and some about the
   other, and sometimes they feel what amounts to an imaginary contention
   because they perceive these two different things as the same.  They are
   both addressed by scaling solutions, but to different degrees.  This is the
   most concrete I can get about my impression whenever someone writes "not
   correct."  Less concrete is my usual impression, "you're both right."

   - "Kicking the can" has value, but no one has connected the value to the
   phrase, so here it is: The more time we have to make changes, the better
   the changes will be.  Of course it's a trade-off (because we suffer through
   that extra time with the unsolved problem), but using (or thinking of)
   "kicking the can" as bad is a mistake.

   - Whether or not there is a massive campaign targeting *current
   bitcoiners* has a very strong effect on upgrade rates.

It seems that a hardfork to a 2MB limit on 5/5/16 is a tad more than one
LOC, since we want an if-then around it so it doesn't happen til the agreed
date.  But I still support it.

On Fri, Dec 18, 2015 at 11:50 PM, Mark Friedenbach via bitcoin-dev <
bitcoin-dev at lists.linuxfoundation.org> wrote:

> Not entirely correct, no. Edge cases also matter. Segwit is described as
> 4MB because that is the largest possible combined block size that can be
> constructed. BIP 102 + segwit would allow a maximum relay of 8MB. So you
> have to be confident that an 8MB relay size would be acceptable, even if a
> block full of actual transactions would be closer to 3.5MB.
>
> On Fri, Dec 18, 2015 at 6:01 PM, sickpig--- via bitcoin-dev <
> bitcoin-dev at lists.linuxfoundation.org> wrote:
>
>> Anthony,
>>
>>
>> On Thu, Dec 17, 2015 at 6:55 PM, Anthony Towns via bitcoin-dev <
>> bitcoin-dev at lists.linuxfoundation.org> wrote:
>>
>>> On Thu, Dec 17, 2015 at 04:51:19PM +0100, sickpig--- via bitcoin-dev
>>> wrote:
>>> > On Thu, Dec 17, 2015 at 2:09 PM, Jorge Timón wrote:
>>> > > Unless I'm missing something, 2 mb x4 = 8mb, so bip102 + SW is
>>> already
>>> > > equivalent to the 2-4-8 "compromise" proposal [...]
>>> > isn't SegWit gain ~75%? hence 2mb x 1.75 = 3.5.
>>>
>>> Segwit as proposed gives a 75% *discount* to witness data with the
>>> same limit, so at a 1MB limit, that might give you (eg) 2.05MB made up
>>> of 650kB of base block data plus 1.4MB of witness data; where 650kB +
>>> 1.4MB/4 = 1MB at the 1MB limit; or 4.1MB made up of 1.3MB of base plus
>>> 2.8MB of witness, for 1.3MB+2.8MB/4 = 2MB at a 2MB limit.
>>>
>>> > 4x is theoric gain you get in case of 2-2 multisig txs.
>>>
>>> With segregated witness, 2-2 multisig transactions are made up of 94B
>>> of base data, plus about 214B of witness data; discounting the witness
>>> data by 75% gives 94+214/4=148 bytes. That compares to about 301B for
>>> a 2-2 multisig transaction with P2SH rather than segwit, and 301/148
>>> gives about a 2.03x gain, not a 4x gain. A 2.05x gain is what I assumed
>>> to get the numbers above.
>>>
>>> You get further improvements with, eg, 3-of-3 multisig, but to get
>>> the full, theoretical 4x gain you'd need a fairly degenerate looking
>>> transaction.
>>>
>>> Pay to public key hash with segwit lets you move about half the
>>> transaction data into the witness, giving about a 1.6x improvement by
>>> my count (eg 1.6MB = 800kB of base data plus 800kB of witness data,
>>> where 800kB+800kB/4=1MB), so I think a gain of between 1.6 and 2.0 is
>>> a reasonable expectation to have for the proposed segwit scheme overall.
>>>
>>>
>> many thanks for the explanation.
>>
>> so it should be fair to say that BIP 102 + SW would bring a gain between
>> 2*1.6 and 2*2.
>>
>> Just for the sake of simplicity if we take the middle of the interval we
>> could say
>> that BIP102 + SW will bring us a max block (virtual) size equal to 1MB *
>> 2 * 1.8 = 3.6
>>
>> Is it right?
>>
>>
>>
>>
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>> https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev
>>
>>
>
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>


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