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From: Rusty Russell <rusty@rustcorp.com.au>
To: Matt Corallo <lf-lists@mattcorallo.com>,
	bitcoin-dev@lists.linuxfoundation.org
Cc: lightning-dev@lists.linuxfoundation.org
Subject: Re: [bitcoin-dev] [Lightning-dev] CPFP Carve-Out for Fee-Prediction Issues in Contracting Applications (eg Lightning)
Date: Tue, 04 Dec 2018 14:03:53 +1030	[thread overview]
Message-ID: <878t163qzi.fsf@rustcorp.com.au> (raw)
In-Reply-To: <c3f68b73-84c6-7428-4bf6-b47802141392@mattcorallo.com>

Matt Corallo <lf-lists@mattcorallo.com> writes:
> As an alternative proposal, at various points there have been 
> discussions around solving the "RBF-pinning" problem by allowing 
> transactors to mark their transactions as "likely-to-be-RBF'ed", which 
> could enable a relay policy where children of such transactions would be 
> rejected unless the resulting package would be "near the top of the 
> mempool". This would theoretically imply such attacks are not possible 
> to pull off consistently, as any "transaction-delaying" channel 
> participant will have to place the package containing A at an effective 
> feerate which makes confirmation to occur soon with some likelihood. It 
> is, however, possible to pull off this attack with low probability in 
> case of feerate spikes right after broadcast.

I like this idea.

Firstly, it's incentive-compatible[1]: assuming blocks are full, miners
should always take a higher feerate tx if that tx would be in the
current block and the replaced txs would not.[2]

Secondly, it reduces the problem that the current lightning proposal
adds to the UTXO set with two anyone-can-spend txs for 1000 satoshis,
which might be too small to cleanup later.  This rule would allow a
simple single P2WSH(OP_TRUE) output, or, with IsStandard changed,
a literal OP_TRUE.

> Note that this clearly relies on some form of package relay, which comes 
> with its own challenges, but I'll start a separate thread on that.

Could be done client-side, right?  Do a quick check if this is above 250
satoshi per kweight but below minrelayfee, put it in a side-cache with a
60 second timeout sweep.  If something comes in which depends on it
which is above minrelayfee, then process them as a pair[3].

Cheers,
Rusty.
[1] Miners have generally been happy with Defaults Which Are Good For The
    Network, but I feel a long term development aim should to be reduce
    such cases to smaller and smaller corners.
[2] The actual condition is subtler, but this is a clear subset AFAICT.
[3] For Lightning, we don't care about child-pays-for-grandparent etc.


  parent reply	other threads:[~2018-12-04  3:34 UTC|newest]

Thread overview: 19+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-11-29 19:37 [bitcoin-dev] CPFP Carve-Out for Fee-Prediction Issues in Contracting Applications (eg Lightning) Matt Corallo
2018-11-30 17:38 ` Russell O'Connor
2018-11-30 19:33   ` Matt Corallo
2018-12-02 15:08 ` Bob McElrath
2018-12-03  4:16   ` [bitcoin-dev] [Lightning-dev] " ZmnSCPxj
2018-12-04  3:33 ` Rusty Russell [this message]
2019-01-07 15:18   ` Matt Corallo
2019-01-08  5:50     ` Rusty Russell
2019-01-08 14:46       ` Matt Corallo
2019-02-13  4:22         ` Rusty Russell
2019-10-24 13:49           ` Johan Torås Halseth
2019-10-24 21:25             ` Matt Corallo
2019-10-25  7:05               ` Johan Torås Halseth
2019-10-25 17:30                 ` Matt Corallo
2019-10-27 19:13                   ` Jeremy
2019-10-28  9:45                     ` Johan Torås Halseth
2019-10-28 17:14                       ` David A. Harding
2019-10-30  7:22                         ` Johan Torås Halseth
2019-10-27 22:54             ` David A. Harding

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