Subject: [bitcoindev] Re: Relax OP_RETURN standardness restrictions

From: /dev /fd0 <[email-masked]>
Date: Fri, 2 May 2025 12:04:13 -0700 (PDT)

Hi Greg,

> Some Bitcoiners are of the opinion that they still want a knob, I think 
doing so is a disrespectful placebo[*] but I don't have a strong opinion if 
an option remains-- 
> the code is safer and cleaner without some filtering rules that few users 
would use but that really just a question between software maintainers and 
users.
> That said, Bitcoin core has generally not had knobs to adjust relay 
policy as distinct from mining policy in large part because of the design 
assumption that the
> two need to be the same.  But in this case if there were a knob here I 
think would make more sense for it to control mining policy rather than 
relay policy,
> since it would actually have some effect in the mining context (in 
excluding the txn from your own blocks) while as a relay only thing it is 
impotent.

Config `mempoolfullrbf` was added in July 2022: 
https://github.com/bitcoin/bitcoin/pull/25353
It was made default in August 2024: 
https://github.com/bitcoin/bitcoin/pull/30493
Option was removed in November 2024: 
https://github.com/bitcoin/bitcoin/pull/30592

`datacarrier` and `datacarriersize` already exist, so why is it a big deal 
to remove them after a few months of monitoring the usage with stats? 

/dev/fd0
floppy disk guy

On Friday, May 2, 2025 at 12:17:40 PM UTC+5:30 Greg Maxwell wrote:

> On Thursday, April 17, 2025 at 7:09:23 PM UTC Antoine Poinsot wrote:
>
>
> Since the restrictions on the usage of OP_RETURN outputs encourage harmful 
> practices while being ineffective in deterring unwanted usage, i propose to 
> drop them. 
>
>
> The situation is even somewhat worse than that:  There are a number of 
> design decisions where it's generally assumed that relay and mining policy 
> generally match, or at least that mismatches are short lived.
>
> When relay policy is more restrictive than what is actually being mined 
> there are at least two serious negative effects.
>
> The first is that the latency of block propagation is greatly harmed,  a 
> single missed transaction causes a tripling of the per hop transmission 
> delay.  If the missed transaction(s) are larger than the TCP window then 
> the increase may be many round trip times.  Also if the missed data is 
> large the currently unused prefill mechanism in compact blocks wouldn't 
> help (and would instead likely make things worse as then nodes will get 
> several times the same transaction data from different peers and you cannot 
> decode the compact block until all the prefill data has been received due 
> to the message checksum.  Delays in block propagation can have a 
> disproportionate effect on mining centralization because they cause larger 
> miners to have improved profitability over smaller ones. This happens 
> regardless of which party was on which side of the delay, no matter which 
> side is delayed its the smaller miner's expected profits that are 
> diminisned and the nature of mining competition means that less profitable 
> miners go bankrupt.
>
> This also encourages the establishment of direct miner submission which 
> can undermine the permissionless nature of bitcoin and in particular again 
> shifts profits towards larger miners because e.g. few would bother 
> connecting to a 1% miner's direct submission interface (if they could even 
> afford to make one).
>
> There are also a number of less significant harms, e.g. more restrictive 
> relay policy makes fee estimation less accurate/complete (though at least 
> estimation is designed to be fairly robust in that direction). 
>
> So on this basis I suggest a principle for these sorts of policy:   Relay 
> rules should admit all transactions which are reliably being mined.
>
> I think node software should adopt this principal as a general rule.
>
> Admitting the transactions is not endorsing them, it's just a recognition 
> of reality.  This policy or equivalent is also the requirement to not 
> suffer from the downsides of relay being more restrictive than mining.   If 
> we imagine that a miner is mining some kind of harmful attack transaction 
> e.g. a validation DOS attack, then the miner needs to be convinced to stop, 
> the implementation changed to not have bad performance, and/or consensus 
> rules must be changed ... but relay policy can't address it.
>
> By general rule I mean that should something like a miner begin mining 
> e.g. quadratic hashing bloat legacy txn, or using unused 
> opcode/successcode/version number or whatever by mistake or technical 
> ignorance there is no need to rush off enabling their relay. A general rule 
> isn't a suicide pact.  But if it were the case that transactions misusing a 
> particular forward compatibility feature were reliably getting mined then 
> that feature would just no longer be useful for forward compatibility 
> regardless of what relay policy says about it and it would be better to 
> relay them than have the downsides of not doing so.
>
> As Antoine Poinsot points out, the existent rule is entirely ineffectual:  
> Parties current bypass these rules with other transaction forms (such as 
> very harmful address stuffing which is impossible to block) or by direct 
> miner submission, which will continue considering the millions of dollars 
> miners have received mining transactions with violate the relay rules.  
> Because of this it will not become effectual with time or tweaking.  It is 
> a dead parrot^policy.  This is no surprise, since it's a product of 
> Bitcoin's anti-censorship properties that *generally* filtering will not 
> work except on the fringes.  As such there isn't practical upside to 
> keeping filtering beyond what miners currently perform. 
>
> Some Bitcoiners are of the opinion that they still want a knob, I think 
> doing so is a disrespectful placebo[*] but I don't have a strong opinion if 
> an option remains-- the code is safer and cleaner without some filtering 
> rules that few users would use but that really just a question between 
> software maintainers and users.  That said, Bitcoin core has generally not 
> had knobs to adjust relay policy as distinct from mining policy in large 
> part because of the design assumption that the two need to be the same.  
> But in this case if there were a knob here I think would make more sense 
> for it to control mining policy rather than relay policy, since it would 
> actually have some effect in the mining context (in excluding the txn from 
> your own blocks) while as a relay only thing it is impotent.
>  
>
> [*] It doesn't even conserve their resources meaningfully.  They'll still 
> receive and process the txn, then discard.  Then they likely have to fetch 
> it a second time when it shows up in a block.  Although they may save 
> re-transmitting it, on average network wide each transaction is sent once 
> and received once so the extra transmission for the block should offset the 
> relay savings.
>
>
>
>

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