[Bitcoin-development] Cost savings by using replace-by-fee, 30-90%

Mark Friedenbach mark at friedenbach.org
Tue May 26 20:56:06 UTC 2015


Please let's at least have some civility and decorum on this list.

On Tue, May 26, 2015 at 1:30 PM, <joliver at airmail.cc> wrote:

> You're the Chief Scientist of __ViaCoin__ a alt with 30 second blocks
> and you have big banks as clients. Shit like replace-by-fee and leading
> the anti-scaling mob is for your clients, not Bitcoin. Get the fuck out.
>
> Peter Todd - 8930511 Canada Ltd.
> 1214-1423 Mississauga Valley Blvd.
> Mississauga ON L5A 4A5
> Canada
>
>
> https://www.ic.gc.ca/app/scr/cc/CorporationsCanada/fdrlCrpDtls.html?corpId=8930511
>
> On 2015-05-26 00:10, Peter Todd wrote:
> > On Tue, May 26, 2015 at 12:03:09AM +0200, Mike Hearn wrote:
> >> CPFP also solves it just fine.
> >
> > CPFP is a significantly more expensive way of paying fees than RBF,
> > particularly for the use-case of defragmenting outputs, with cost
> > savings ranging from 30% to 90%
> >
> >
> > Case 1: CPFP vs. RBF for increasing the fee on a single tx
> > ----------------------------------------------------------
> >
> > Creating an spending a P2PKH output uses 34 bytes of txout, and 148
> > bytes of txin, 182 bytes total.
> >
> > Let's suppose I have a 1 BTC P2PKH output and I want to pay 0.1 BTC to
> > Alice. This results in a 1in/2out transaction t1 that's 226 bytes in
> > size.
> > I forget to click on the "priority fee" option, so it goes out with the
> > minimum fee of 2.26uBTC. Whoops! I use CPFP to spend that output,
> > creating a new transaction t2 that's 192 bytes in size. I want to pay
> > 1mBTC/KB for a fast confirmation, so I'm now paying 418uBTC of
> > transaction fees.
> >
> > On the other hand, had I use RBF, my wallet would have simply
> > rebroadcast t1 with the change address decreased. The rules require you
> > to pay 2.26uBTC for the bandwidth consumed broadcasting it, plus the
> > new
> > fee level, or 218uBTC of fees in total.
> >
> > Cost savings: 48%
> >
> >
> > Case 2: Paying multiple recipients in succession
> > ------------------------------------------------
> >
> > Suppose that after I pay Alice, I also decide to pay Bob for his hard
> > work demonstrating cryptographic protocols. I need to create a new
> > transaction t2 spending t1's change address. Normally t2 would be
> > another 226 bytes in size, resulting in 226uBTC additional fees.
> >
> > With RBF on the other hand I can simply double-spend t1 with a
> > transaction paying both Alice and Bob. This new transaction is 260
> > bytes
> > in size. I have to pay 2.6uBTC additional fees to pay for the bandwidth
> > consumed broadcasting it, resulting in an additional 36uBTC of fees.
> >
> > Cost savings: 84%
> >
> >
> > Case 3: Paying multiple recipients from a 2-of-3 multisig wallet
> > ----------------------------------------------------------------
> >
> > The above situation gets even worse with multisig. t1 in the multisig
> > case is 367 bytes; t2 another 367 bytes, costing an additional 367uBTC
> > in fees. With RBF we rewrite t1 with an additional output, resulting in
> > a 399 byte transaction, with just 36uBTC in additional fees.
> >
> > Cost savings: 90%
> >
> >
> > Case 4: Dust defragmentation
> > ----------------------------
> >
> > My wallet has a two transaction outputs that it wants to combine into
> > one for the purpose of UTXO defragmentation. It broadcasts transaction
> > t1 with two inputs and one output, size 340 bytes, paying zero fees.
> >
> > Prior to the transaction confirming I find I need to spend those funds
> > for a priority transaction at the 1mBTC/KB fee level. This transaction,
> > t2a, has one input and two outputs, 226 bytes in size. However it needs
> > to pay fees for both transactions at once, resulting in a combined
> > total
> > fee of 556uBTC. If this situation happens frequently, defragmenting
> > UTXOs is likely to cost more in additional fees than it saves.
> >
> > With RBF I'd simply doublespend t1 with a 2-in-2-out transaction 374
> > bytes in size, paying 374uBTC. Even better, if one of the two inputs is
> > sufficiently large to cover my costs I can doublespend t1 with a
> > 1-in-2-out tx just 226 bytes in size, paying 226uBTC.
> >
> > Cost savings: 32% to 59%, or even infinite if defragmentation w/o RBF
> >               costs you more than you save
> >
> >
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