From: "=?UTF-8?Q?Ad=c3=a1n_S=c3=a1nchez_de_Pedro_Crespo?=" <adan@stampery.co>
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To: bitcoin-dev@lists.linuxfoundation.org
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Date: Thu, 19 Oct 2017 15:41:51 +0200
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Subject: Re: [bitcoin-dev] Improving Scalability via Block Time Decrease
Precedence: list

Blockchains with fast confirmation times are currently believed to
suffer from reduced security due to a high stale rate.

As blocks take a certain time to propagate through the network, if miner
A mines a block and then miner B happens to mine another block before
miner A's block propagates to B, miner B's block will end up wasted and
will not "contribute to network security".

Furthermore, there is a centralization issue: if miner A is a mining
pool with 30% hashpower and B has 10% hashpower, A will have a risk of
producing a stale block 70% of the time (since the other 30% of the time
A produced the last block and so will get mining data immediately)
whereas B will have a risk of producing a stale block 90% of the time.

Thus, if the block interval is short enough for the stale rate
to be high, A will be substantially more efficient simply by virtue of
its size. With these two effects combined, blockchains which produce
blocks quickly are very likely to lead to one mining pool having a large
enough percentage of the network hashpower to have de facto control over
the mining process.

Another possible implication of reducing the average block time is that
block size should be reduced accordingly. In an hypothetical 5 minutes
block size Bitcoin blockchain, there would be twice the block space
available for miners to include transactions, which could lead to 2
immediate consequences: (1) the blockchain could grow up to twice the
rate, which is known to be bad for decentralization; and (2) transaction
fees might go down, making it cheaper for spammers to bloat our beloved
UTXO sets.

There have been numerous proposals that tried to overcome the downsides
of faster blocks, the most noteworthy probably being the "Greedy
Heaviest Observed Subtree" (GHOST) protocol:
http://www.cs.huji.ac.il/~yoni_sompo/pubs/15/btc_scalability_full.pdf

Personally, I can't see why Bitcoin would need or how could it even
benefit at all from faster blocks. Nevertheless, I would really love if
someone in the list who has already run the numbers could bring some
valid points on why 10 minutes is the optimal rate (other than "if it
ain't broke, don't fix it").

-- 
Adán Sánchez de Pedro Crespo
CTO, Stampery Inc.
San Francisco - Madrid