Feedback-ID: i525146e8:Fastmail
Date: Mon, 7 Nov 2022 16:27:16 -0500
From: Peter Todd <pete@petertodd.org>
To: Suhas Daftuar <sdaftuar@gmail.com>,
 Bitcoin Protocol Discussion <bitcoin-dev@lists.linuxfoundation.org>
Message-ID: <Y2l4NK0HC6xsUwSL@petertodd.org>
References: <Y2ln2fJ+8+Q0qS0E@petertodd.org>
 <CAFp6fsH0BXn51DqpJLWn56ecohCJZ+skVvabGBRmjeK5u08vdg@mail.gmail.com>
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In-Reply-To: <CAFp6fsH0BXn51DqpJLWn56ecohCJZ+skVvabGBRmjeK5u08vdg@mail.gmail.com>
Subject: Re: [bitcoin-dev] Removing BIP-125 Rule #5 Pinning with the
 Always-Replaceable Invariant
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On Mon, Nov 07, 2022 at 04:21:11PM -0500, Suhas Daftuar via bitcoin-dev wro=
te:
> Hello bitcoin-dev,
>=20
> The description in the OP is completely broken for the simple reason that
> Bitcoin transactions can have multiple inputs, and so a single transaction
> can conflict with multiple in-mempool transactions. The proposal would
> limit the number of descendants of each in-mempool transaction to
> MAX_REPLACEMENT_CANDIDATES (note that this is duplicative of the existing
> Bitcoin Core descendant limits), but a transaction that has, say, 500
> inputs might arrive and conflict with 500 unrelated in-mempool
> transactions. This could result in 12,500 evictions -- far more than the
> 100 that was intended.

That's easy to fix: just sum up the number of nReplacementCandidates for ea=
ch
input in the multiple input case. Again, it'll overcount in the diamond cas=
e.
But so does the existing code.

The goal is to defeat pinning by ensuring that you can always replace a
transaction by double-spending an output; not that any possible way of
double-spending multiple outputs at once would work.

--=20
https://petertodd.org 'peter'[:-1]@petertodd.org

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