Subject: Re: [bitcoindev] [BIP Proposal] Mempool Validation and Relay Policies via User-Defined Scripts

From: Garlo Nicon <[email-masked]>
Date: Fri, 26 Sep 2025 09:58:26 +0200

> You cannot pick and choose which parts of a block you like and which
parts are "abusive".

In the current implementation, yes. But if you accept a proof, that a block
is valid, instead of accepting a block in plaintext, then you can land on
the same chain. Because after all, pruned nodes care only about the last
288 blocks, or something like that. If they can update their UTXO set, and
always land on a valid chain, then they don't need transaction data in
plaintext. They just need to update their UTXO database in a way, where
attacking it would require breaking ECDSA, SHA-256, or similar things (a
proof-based system, which would not weaken existing cryptographic
assumptions, would be sufficient).

And the same is true about Initial Blockchain Download. Only today, you
have to download hundreds of GBs, to synchronize the new node from scratch.
But it can be changed, and as the size of the whole chain will grow, people
will be pushed, to start deploying some optimizations. Otherwise, there
will be even less nodes, if node operators will decide to trust centralized
solutions instead, or do things, which already happened in some altcoins,
where people passed around an already synced node data, and trusted, that
it is valid (especially in CPU-mined coins, where verifying thousands
blocks required similar effort, than mining a new block).

pt., 26 wrz 2025 o 02:25 Andrew Poelstra <[email-masked]>
napisał(a):

> On Thu, Sep 25, 2025 at 11:52:02AM -0600, Chris Guida wrote:
> >
> > Anyway, forcing users to relay transactions they consider abusive if they
> > want to relay any transactions at all does not seem in keeping with
> > bitcoin's ethos, not to mention that it obviously would never work.
> >
>
> Once a transaction is in a block, you need to relay the transaction if
> you want to relay a block. You cannot pick and choose which parts of a
> block you like and which parts are "abusive". This is what it means for
> something to be a consensus system.
>
> The purpose of the mempool is to approximate the contents of blocks,
> both to help individual node operators (who would otherwise get large
> quantities of "surprise transactions" with every block) and to help the
> network (which would otherwise have poor propagation properties).
>
> Any sort of filtering beyond that done by miners is contrary to this
> purpose of the mempool. This is a technical fact. It has nothing to do
> with "bitcoin's ethos", except its ethos as a consensus system, which
> directly contradicts your point.
>
> --
> Andrew Poelstra
> Director, Blockstream Research
> Email: apoelstra at wpsoftware.net
> Web:   https://www.wpsoftware.net/andrew
>
> The sun is always shining in space
>     -Justin Lewis-Webster
>
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