Re: [bitcoin-dev] Unlimited Max Blocksize (reprise)

[Daniele Pinna <daniele.pinna@gmail.com>]

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I think that the argument for Peter's optimal block construction algorithm
(leading to the definition of the Fee Demand Curve) is that in the limit of
a mempool with a very large number of transactions, you should be able to
assume that for any given transaction [image: i] of size [image: s_i] and
fee density [image: \phi_i], many transactions [image: j] will exist such
that [image: s_j<s_i] and [image: \phi_j=\phi_i]. This means that, in
solving the knapsack problem, one has the choice of including what
effectively amounts to fractions of transactions. This in turn results in
an unbounded knapsack problem for which Peter's greedy algorithm is an
asymptotically optimal solution.

Obviously this breaks down in small mempool scenarios where the
discreteness of transactions can not be washed away (such as the current
state of the network).

I hope this clarifies your point.

Daniele

---------- Forwarded message ----------
From: Daniele Pinna <daniele.pinna@gmail.com>
Date: Sun, Aug 30, 2015 at 1:11 PM
Subject: Another issue with the Fee Demand curve
To: Peter R <peter_r@gmx.com>


This was pointed out to me by Tom Harding.

Choosing what the optimal way of choosing transactions to be included in a
block is a knapsack problem (an NP-complete problem!):

https://en.wikipedia.org/wiki/Knapsack_problem

For which your suggested solution, which is by no means exact, is known as
the "Greedy Approximation Algorithm". This algorithm in turn works best
only when a very large quantity of high density transactions is available
in the mempool.

This wouldn't invalidate your proof but it may significantly alter the
optimal block size value.

Just thought I would throw this your way.

Daniele

---------- Forwarded message ----------
From: Tom Harding <tomh@thinlink.com>
Date: Sat, Aug 29, 2015 at 10:21 PM
Subject: Re: [bitcoin-dev] Unlimited Max Blocksize (reprise)
To: Daniele Pinna <daniele.pinna@gmail.com>


Daniele --

Thanks!  I printed it and read the whole thing.  It's really a great step
forward building on the Peter R paper. The conclusions are enticing.  I'm
looking forward to understanding it in more detail and participating in the
discussion.

I find your work to be rational and scholarly without being obscure,
pedantic, or getting caught up in unimportant details.  It has a long-term
focus.


"The optimal strategy, first analyzed in [3]"  I don't recall whether Peter
R considered constrained block space or not, but if it is considered,
simple fee-density prioritization is not necessarily optimal (it is a
knapsack problem).




On 8/29/2015 10:16 AM, Daniele Pinna wrote:

Here you go Tom!

https://www.scribd.com/doc/276849939/On-the-Nature-of-Miner-Advantages-in-Uncapped-Block-Size-Fee-Markets

Daniele Pinna, Ph.D

On Thu, Aug 27, 2015 at 12:59 AM, Tom Harding <tomh@thinlink.com> wrote:

>
> Thanks for posting this.  I'm very interested to read your paper when it
> is available.
>
>
>
> On 8/26/2015 3:22 PM, Daniele Pinna via bitcoin-dev wrote:
>
> I don't get how it's very risky to have the Mike and Gavin redirect the
> course of the bitcoin protocol but it's totally fine to consider complex
> miner voting protocols as a hard fork option.
>
> I believe that this community has not given due weight to the analysis
> proposed by Peter__R on the existence of fee markets with  uncapped max
> blocksizes. The critiques made toward his work were in no way definitive
> and discussion just stopped. Is it the math that bothers people?
>
> If his work stands the test of scrutiny, then a controlled raising of the
> max blocksize in the interim to ease into the fee market dynamic described
> is the best option. Possibly a stepwise BIP101 where the community
> hardforks every two years until we all trust the fee market dynamics.
>
> The main critique to uncapped max blocksizes which I've heard stems from
> our incapacity to quantify the advantages that large miners have over
> smaller ones. As I will show in an upcoming paper, these advantages do not
> stem from the act of propagating large blocks but rather from the block
> subsidies which allow miners to mine unnecessary large blocks irregardless
> of the fees contained therein. One typical example is Peter Todd's
> suggested attack whereby a miner creates a massive block filled with spam
> transactions that pay himself solely to slow down the rest of the network
> and gain an advantage. Putting aside the increased orphan risk arising from
> the propagation of such a large block, this attack would never be viable if
> it weren't for the existence of current block subsidies.
>
> As such, exponential increases to the max blocksize make perfect sense
> since the block reward decreases exponentially also. All arguments invoking
> rates of technological advances (see Gavin's original posts) don't mean
> anything. Rational miners will NOT be incentivized to mine gargantuan spam
> filled blocks in the presence of a vanishing block reward.
>
> I truly hope this matter gets the consideration it deserves. Particularly
> with the upcoming scaling workshops.
>
> Dpinna
> On Aug 21, 2015 11:35 PM, "Daniele Pinna" <daniele.pinna@gmail.com> wrote:
>
> "I ran some simulations, and if blocks take 20 seconds to propagate, a
> network with a miner that has 30% of the hashing power will get 30.3% of
> the blocks."
>
> Peter_R's analysis of fee markets in the absence of blocksize limits [1]
> shows that the hashrate advantage of a large miner is a side-effect of
> coinbase subsidization. As the block rewards get smaller, so will large
> miner advantages. An easy way to think about this is as follows:
>
> Currently, the main critique of larger blocksizes is that we'll connected
> miners can cut out smaller miners by gratuitously filling up blocks with
> self-paying transactions. This only works because block subsidies exist.
> The moment block rewards become comparable to block TX fees, this exploit
> ceases to be functional.
>
> Basically, large miners will still be forced to move full blocks, but it
> will go against their interest to fill them with spam since their main
> source of income is the fees themselves. As a result, large miners (unlike
> smaller ones) will lose the incentive to mine an un full block this evening
> the playing                           field.
>
> In this context, large blocksizes as proposed by BIP100-101 hope to
> stimulate the increase of TX fees by augmenting the network's capacity. The
> sooner block rewards become comparable to block fees, the sooner we will
> get rid of mine centralization.
>
> Dpinna
>
> [1]
> http://www.scribd.com/mobile/doc/273443462/A-Transaction-Fee-Market-Exists-Without-a-Block-Size-Limit
>
>

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