Lets talk about block time

The point of this thread is to start a productive discussion about the pros and cons of changing block time, and get a better understanding of what impacts both good and bad, it will have on users, businesses, exchanges, miners, devs, etc.

Here is what I understand about block time so far, and how it impacts these different groups of people. Please correct me if I am wrong, I am far from an expert.

  1. Decreasing block time increases the frequency of orphaned blocks which decreases miner profitability. Unless we add something that ETH does where uncle (orphaned) blocks are rewarded coins.
  2. Decreasing block time decreases the variance in time it takes for a transaction to be confirmed.
  3. Decreasing block time makes each block individually weaker as less hash power is securing each block. This could make individual blocks more vulnerable to be maliciously orphaned and make double spending confirmed transactions less costly.
  4. Decreasing block time would improve user experience because confirmation time would have less variance.
  5. Decreasing block time would give businesses the option to accept a faster 1 block confirmation for transactions if they are comfortable with it being backed by less hash power security. This would also make the user experience better.
  6. I understand 0-confirmation is relatively safe for small amounts, but I think most businesses feel much safer if they wait to accept at least 1 confirmation just to make sure everything is okay, myself included.

Questions I have about block time:

  1. Do we know why Satoshi choose 10 minutes for block time? Was it because 2009 tech was slower? If Satoshi was creating Bitcoin today in 2021 what block time do you think he would choose?

  2. In reference to point (3) above. How likely is it that a double spend attack would happen on a shorter block time? Would honest miners come to the rescue to stop a double spend attack? Similar to how honest miners have defended BCH when it came to contentious forks.

  3. I have discussed with crypto users ( mostly traders ) why they choose a coin like LTC over BCH and one of the reasons is because they can move their coins faster between exchanges. Now I understand LTC is the dominant coin for the Scrypt algo which means its less vulnerable to be attacked as it has the most amount of hash power for its algo. While BCH using the sha256 algo only has ~2% of the hash power of BTC. I assume this is the reason why exchanges are more laxed on confirmation times for LTC over BCH. Is there anything BCH can do that would increase the confidence in exchanges to be more laxed on confirmation time or do we just have to wait until we have a bigger % of the sha256 hash power? If we did decrease block time for BCH would it help traders? Or would exchanges just increase the # of block confirmations required because they think BCH is vulnerable to double spend attacks?

  4. In reference to point (6) above. How different is it in terms of security for a business to accept a 0-confirmation transaction or waiting for say a single 15 second block confirmation? Cause I feel I would trust the latter much more even if hash power was weak.


Vitalik Buterin has written a great piece on the considerations involved in choosing block time: On Slow and Fast Block Times | Ethereum Foundation Blog

Regarding your points:

  • Point 1: With shorter block times, the blocks are also smaller, so the main issue here is the fixed component of block propagation and validation time independent of block size - which indeed increases orphan rate. But there is a lot of room between our current 10 minutes and ETH’s 17 seconds.
  • Point 3: Double-spending confirmed transactions does not become cheaper if you increase the number of confirmations you wait proportionally to the block time decrease.

Other than that, I think the main challenges are of transitory nature: making sure the DAA, time-based smart contracts, and other processes tied to block height keep running smoothly though the change.

(BTW, Litecoin is no longer the dominant Scrypt coin - it’s been overtaken by Dogecoin. However, unlike BTC-BCH, both coins are merge-mined.)


Can you articulate a problem that will be solved with a shorter block time? It really doesn’t make any sense to me why a consensus rule would be in place because of current exchange policies. If they change their policy tomorrow do we all have another hard fork to adjust to it? Super silly to me.


The two problems I see it solving are the following:

  1. Decreasing block time would give businesses the option to accept a faster 1 block confirmation for transactions if they are comfortable with it being backed by less hash power security. This would also make the user experience better.

For example, I run a service that users can deposit SLP tokens into. I could accept 0-confirmation SLP token deposits, but I rather wait for one block confirmation. Users have to wait anywhere from a few minutes to an hour to wait for this confirmation before they can use their token on my service. If block times were shorter say 2 minutes, and I was comfortable accepting only one 2 minute block worth of hash power security then the user would only have to wait several seconds or up to 10 minutes for a confirmation. This would provide a much better user experience.

  1. Decreasing block time would improve user experience because confirmation time would have less variance.

A user waiting for a single 10 minute block would have more variance than say a user waiting for five 2 minute blocks. Both have same amount of hash power, but 2 minute blocks would be more predictable and have less time variance, which would provide a much better user experience. Instead of waiting anywhere from a few minutes to an hour with a single 10 minute block confirmation, I would guess the variance of five 2 minute blocks would be somewhere between 5 minutes to 20 minutes. Better user experience with 2 minute blocks.

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That problem as far as I know could be solved with fraud proofs which would be much less invasive than a hardfork, not to mention, the user experience enhancement would be negligible vs the risk of splitting the network. Also, I don’t see anyone choosing LTC over BCH. That coin has development that’s been abandoned and BCH routinely is higher in market cap, while, BTC with 10 min blocks has hit 60k.


Just mentioning in case you’re unaware, but @tom 's Double-Spend-Proofs (DSP) do a lot to mitigate the double-spend problem.


If the point of lower block times is to make exchange deposits faster, and lowering block times lowers security proportionally, then it wont likely make exchange deposits faster.

Im going to need more data, not speculation, to convince me lowering block times is good for anything.

Maybe a different approach would be better. 0-conf is what needs security. The best first step is double spend proofs. Further advancements would likely require some form of preconsensus, if done intelligently, such as never mandating block inclusion but only rejecting latercomer doublespends. But that could have bad tradeoffs too.

Decreasing block time would give businesses the option to accept a faster 1 block confirmation for transactions

That is an assumption about how businesses that I don’t think is backed by fact.

First of all, our track record with regards to frauds is enough to allow businesses to accept-as-final a transaction much faster than most do today.

The problem of businesses in today’s crypto landscape is one where it pays to be overly cautious. Likewise it can destroy companies if their risk profile is too low.
This, frankly, is no different than any other starting business-sector and history shows that as tech and expertise grows, user experience in this regard goes up.

When you realize this then the idea of differentiating yourself from the best understood crypto (BTC) is actually counter-productive.

The point to remember is that many companies are accepting a host of coins, they can’t possibly have expertise in all of them. Should one coin start to become the one that is used as money the most, this will change the landscape of crypto dramatically.

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LTC is the dominant coin for the Scrypt algo

That’s no longer the case, because of Doge.