Johan Torås Halseth [ARCHIVE] on Nostr: 📅 Original date posted:2019-10-25 📝 Original message: It essentially changes ...
📅 Original date posted:2019-10-25
📝 Original message:
It essentially changes the rule to always allow CPFP-ing the commitment as
long as there is an output available without any descendants. It changes
the commitment from "you always need at least, and exactly, one non-CSV
output per party. " to "you always need at least one non-CSV output per
party. "
I realize these limits are there for a reason though, but I'm wondering if
could relax them. Also now that jeremyrubin has expressed problems with the
current mempool limits.
On Thu, Oct 24, 2019 at 11:25 PM Matt Corallo <lf-lists at mattcorallo.com>
wrote:
> I may be missing something, but I'm not sure how this changes anything?
>
> If you have a commitment transaction, you always need at least, and
> exactly, one non-CSV output per party. The fact that there is a size
> limitation on the transaction that spends for carve-out purposes only
> effects how many other inputs/outputs you can add, but somehow I doubt
> its ever going to be a large enough number to matter.
>
> Matt
>
> On 10/24/19 1:49 PM, Johan Torås Halseth wrote:
> > Reviving this old thread now that the recently released RC for bitcoind
> > 0.19 includes the above mentioned carve-out rule.
> >
> > In an attempt to pave the way for more robust CPFP of on-chain contracts
> > (Lightning commitment transactions), the carve-out rule was added in
> > https://github.com/bitcoin/bitcoin/pull/15681. However, having worked on
> > an implementation of a new commitment format for utilizing the Bring
> > Your Own Fees strategy using CPFP, I’m wondering if the special case
> > rule should have been relaxed a bit, to avoid the need for adding a 1
> > CSV to all outputs (in case of Lightning this means HTLC scripts would
> > need to be changed to add the CSV delay).
> >
> > Instead, what about letting the rule be
> >
> > The last transaction which is added to a package of dependent
> > transactions in the mempool must:
> > * Have no more than one unconfirmed parent.
> >
> > This would of course allow adding a large transaction to each output of
> > the unconfirmed parent, which in effect would allow an attacker to
> > exceed the MAX_PACKAGE_VIRTUAL_SIZE limit in some cases. However, is
> > this a problem with the current mempool acceptance code in bitcoind? I
> > would imagine evicting transactions based on feerate when the max
> > mempool size is met handles this, but I’m asking since it seems like
> > there has been several changes to the acceptance code and eviction
> > policy since the limit was first introduced.
> >
> > - Johan
> >
> >
> > On Wed, Feb 13, 2019 at 6:57 AM Rusty Russell <rusty at rustcorp.com.au
> > <mailto:rusty at rustcorp.com.au>> wrote:
> >
> > Matt Corallo <lf-lists at mattcorallo.com
> > <mailto:lf-lists at mattcorallo.com>> writes:
> > >>> Thus, even if you imagine a steady-state mempool growth, unless
> the
> > >>> "near the top of the mempool" criteria is "near the top of the
> next
> > >>> block" (which is obviously *not* incentive-compatible)
> > >>
> > >> I was defining "top of mempool" as "in the first 4 MSipa", ie.
> next
> > >> block, and assumed you'd only allow RBF if the old package wasn't
> > in the
> > >> top and the replacement would be. That seems incentive
> > compatible; more
> > >> than the current scheme?
> > >
> > > My point was, because of block time variance, even that criteria
> > doesn't hold up. If you assume a steady flow of new transactions and
> > one or two blocks come in "late", suddenly "top 4MWeight" isn't
> > likely to get confirmed until a few blocks come in "early". Given
> > block variance within a 12 block window, this is a relatively likely
> > scenario.
> >
> > [ Digging through old mail. ]
> >
> > Doesn't really matter. Lightning close algorithm would be:
> >
> > 1. Give bitcoind unileratal close.
> > 2. Ask bitcoind what current expidited fee is (or survey your
> mempool).
> > 3. Give bitcoind child "push" tx at that total feerate.
> > 4. If next block doesn't contain unilateral close tx, goto 2.
> >
> > In this case, if you allow a simpified RBF where 'you can replace if
> > 1. feerate is higher, 2. new tx is in first 4Msipa of mempool, 3.
> > old tx isnt',
> > it works.
> >
> > It allows someone 100k of free tx spam, sure. But it's simple.
> >
> > We could further restrict it by marking the unilateral close somehow
> to
> > say "gonna be pushed" and further limiting the child tx weight (say,
> > 5kSipa?) in that case.
> >
> > Cheers,
> > Rusty.
> > _______________________________________________
> > Lightning-dev mailing list
> > Lightning-dev at lists.linuxfoundation.org
> > <mailto:Lightning-dev at lists.linuxfoundation.org>
> > https://lists.linuxfoundation.org/mailman/listinfo/lightning-dev
> >
>
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📝 Original message:
It essentially changes the rule to always allow CPFP-ing the commitment as
long as there is an output available without any descendants. It changes
the commitment from "you always need at least, and exactly, one non-CSV
output per party. " to "you always need at least one non-CSV output per
party. "
I realize these limits are there for a reason though, but I'm wondering if
could relax them. Also now that jeremyrubin has expressed problems with the
current mempool limits.
On Thu, Oct 24, 2019 at 11:25 PM Matt Corallo <lf-lists at mattcorallo.com>
wrote:
> I may be missing something, but I'm not sure how this changes anything?
>
> If you have a commitment transaction, you always need at least, and
> exactly, one non-CSV output per party. The fact that there is a size
> limitation on the transaction that spends for carve-out purposes only
> effects how many other inputs/outputs you can add, but somehow I doubt
> its ever going to be a large enough number to matter.
>
> Matt
>
> On 10/24/19 1:49 PM, Johan Torås Halseth wrote:
> > Reviving this old thread now that the recently released RC for bitcoind
> > 0.19 includes the above mentioned carve-out rule.
> >
> > In an attempt to pave the way for more robust CPFP of on-chain contracts
> > (Lightning commitment transactions), the carve-out rule was added in
> > https://github.com/bitcoin/bitcoin/pull/15681. However, having worked on
> > an implementation of a new commitment format for utilizing the Bring
> > Your Own Fees strategy using CPFP, I’m wondering if the special case
> > rule should have been relaxed a bit, to avoid the need for adding a 1
> > CSV to all outputs (in case of Lightning this means HTLC scripts would
> > need to be changed to add the CSV delay).
> >
> > Instead, what about letting the rule be
> >
> > The last transaction which is added to a package of dependent
> > transactions in the mempool must:
> > * Have no more than one unconfirmed parent.
> >
> > This would of course allow adding a large transaction to each output of
> > the unconfirmed parent, which in effect would allow an attacker to
> > exceed the MAX_PACKAGE_VIRTUAL_SIZE limit in some cases. However, is
> > this a problem with the current mempool acceptance code in bitcoind? I
> > would imagine evicting transactions based on feerate when the max
> > mempool size is met handles this, but I’m asking since it seems like
> > there has been several changes to the acceptance code and eviction
> > policy since the limit was first introduced.
> >
> > - Johan
> >
> >
> > On Wed, Feb 13, 2019 at 6:57 AM Rusty Russell <rusty at rustcorp.com.au
> > <mailto:rusty at rustcorp.com.au>> wrote:
> >
> > Matt Corallo <lf-lists at mattcorallo.com
> > <mailto:lf-lists at mattcorallo.com>> writes:
> > >>> Thus, even if you imagine a steady-state mempool growth, unless
> the
> > >>> "near the top of the mempool" criteria is "near the top of the
> next
> > >>> block" (which is obviously *not* incentive-compatible)
> > >>
> > >> I was defining "top of mempool" as "in the first 4 MSipa", ie.
> next
> > >> block, and assumed you'd only allow RBF if the old package wasn't
> > in the
> > >> top and the replacement would be. That seems incentive
> > compatible; more
> > >> than the current scheme?
> > >
> > > My point was, because of block time variance, even that criteria
> > doesn't hold up. If you assume a steady flow of new transactions and
> > one or two blocks come in "late", suddenly "top 4MWeight" isn't
> > likely to get confirmed until a few blocks come in "early". Given
> > block variance within a 12 block window, this is a relatively likely
> > scenario.
> >
> > [ Digging through old mail. ]
> >
> > Doesn't really matter. Lightning close algorithm would be:
> >
> > 1. Give bitcoind unileratal close.
> > 2. Ask bitcoind what current expidited fee is (or survey your
> mempool).
> > 3. Give bitcoind child "push" tx at that total feerate.
> > 4. If next block doesn't contain unilateral close tx, goto 2.
> >
> > In this case, if you allow a simpified RBF where 'you can replace if
> > 1. feerate is higher, 2. new tx is in first 4Msipa of mempool, 3.
> > old tx isnt',
> > it works.
> >
> > It allows someone 100k of free tx spam, sure. But it's simple.
> >
> > We could further restrict it by marking the unilateral close somehow
> to
> > say "gonna be pushed" and further limiting the child tx weight (say,
> > 5kSipa?) in that case.
> >
> > Cheers,
> > Rusty.
> > _______________________________________________
> > Lightning-dev mailing list
> > Lightning-dev at lists.linuxfoundation.org
> > <mailto:Lightning-dev at lists.linuxfoundation.org>
> > https://lists.linuxfoundation.org/mailman/listinfo/lightning-dev
> >
>
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