[bitcoin-dev] BIP proposal: Increase block size limit to 2 megabytes

Jorge Timón jtimon at jtimon.cc
Sat Feb 6 03:14:03 UTC 2016

If it is to be uncontroversial and everybody will upgrade, there's no
fear of a "veto power" and there's no good reason not to wait for 95%
block version signaling for deployment coordination, ideally using
But that's for chosing the exact block where to start. The grace
period to give time to all users to upgrade should be before and not
after miner's final confirmation: that simplifies and accelerates
things. Assuming we chose a grace period that is really adequate,
nearly 100% of miners will have likely upgraded long before everyone
(since miners are a subset of "everyone"). If that is not the case and
miners happen to be the latest to upgrade, using bip9 after the grace
period (aka starting median-time/height) will make sure the hardfork
doesn't get activated without 95% of the miners having upgraded.

28 days seems extremely short (specially if the grace period comes
first), some people have suggested one year for simple hardforks like
this one.

On Sat, Feb 6, 2016 at 1:12 AM, Luke Dashjr via bitcoin-dev
<bitcoin-dev at lists.linuxfoundation.org> wrote:
> On Friday, February 05, 2016 8:51:08 PM Gavin Andresen via bitcoin-dev wrote:
>> Blog post on a couple of the constants chosen:
>>   http://gavinandresen.ninja/seventyfive-twentyeight
> Can you put this in the BIP's Rationale section (which appears to be mis-named
> "Discussion" in the current draft)?
>> Signature operations in un-executed branches of a Script are not counted
>> OP_CHECKMULTISIG evaluations are counted accurately; if the signature for a
>> 1-of-20 OP_CHECKMULTISIG is satisified by the public key nearest the top
>> of the execution stack, it is counted as one signature operation. If it is
>> satisfied by the public key nearest the bottom of the execution stack, it
>> is counted as twenty signature operations. Signature operations involving
>> invalidly encoded signatures or public keys are not counted towards the
>> limit
> These seem like they will break static analysis entirely. That was a noted
> reason for creating BIP 16 to replace BIP 12. Is it no longer a concern? Would
> it make sense to require scripts to commit to the total accurate-sigop count
> to fix this?
>> The amount of data hashed to compute signature hashes is limited to
>> 1,300,000,000 bytes per block.
> The rationale for this wasn't in your blog post. I assume it's based on the
> current theoretical max at 1 MB blocks? Even a high-end PC would probably take
> 40-80 seconds just for the hashing, however - maybe a lower limit would be
> best?
>> Miners express their support for this BIP by ...
> But miners don't get to decide hardforks. How does the economy express their
> support for it? What happens if miners trigger it without consent from the
> economy?
> If you are intent on using the version bits to trigger the hardfork, I suggest
> rephrasing this such that miners should only enable the bit when they have
> independently confirmed economic support (this means implementations need a
> config option that defaults to off).
>> SPV (simple payment validation) wallets are compatible with this change.
> Would prefer if this is corrected to "Light clients" or something. Actual SPV
> wallets do not exist at this time, and would not be compatible with a
> hardfork.
>> In the short term, an increase is needed to continue the current economic
>> policies with regards to fees and block space, matching market expectations
>> and preventing market disruption.
> IMO this sentence is the most controversial part of your draft, and it
> wouldn't suffer a loss to remove it (or at least make it subjective).
> I would also prefer to see any hardfork:
> 1. Address at least the simple tasks on the hardfork wishlist (eg, enable some
>    disabled opcodes; fix P2SH for N-of->15 multisig; etc).
> 2. Be deployed as a soft-hardfork so as not to leave old nodes entirely
>    insecure.
> Luke
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