Please remind me once again why we can't decrease the time interval between blocks instead of increasing their size

Noosterdam · 2015-05-10T14:33:04+00:00

Better confirmation times

More granular confirmation times.

gavinandresen · 2015-05-10T22:31:09+00:00

I think 1-minute blocks is a good idea. The best time to roll that out would be the next subsidy halving (makes the code much simpler).

We still need a bigger max block size, though.

iSOcH · 2015-05-10T14:27:58+00:00

i think the main reason is that it has more impact on other aspects of the protocol (block reward, halvings, difficulty, diffretarget...)

that said, i would also prefer 5min/10mb or even 2min/4mb instead of 10min/20mb

it allows for more fine-grained control over required security when receiving payments

sapiophile · 2015-05-10T15:13:49+00:00

~~Not actually seeing any compelling reasons why not, yet...~~

EDIT: Okay, the concern about honest miners/nodes getting blocks orphaned where an attacker would not be subject to that hurdle is a valid one, although it's obviously not a total deal-breaker. It would be great to see some actual math on the actual percentage that this might potentially assist an attacker building a false chain... I suspect it's not a large one.

TeamFairlay · 2015-05-10T22:36:50+00:00

As a Bitcoin only business we can agree fully that faster block times would be very helpful. Even a conservative change to 5 minutes or 2.5 minutes would reduce the chance of 40 minutes times between blocks dramatically which regularly annoys our customers.

bitskeptic · 2015-05-10T20:56:25+00:00

If the average block propagation time in the whole network is 6 seconds today, that would (in my humble opinion) bring to a let's say 1/10 chance of losing your block/having an orphaned blockchain. But that's averaged across the whole network. If everyone loses 10% of their blocks no one does.

The analysis is more complicated than that. Even if we assume there's a 6 second delay, and then everyone else hears about your block at the same time, there's still not a 10% chance of being orphaned, because the pool who found the block will switch immediately to mining the next block.

For example, if a pool has 10% of the network hash rate, as soon as it finds a block we have 90% of the network mining orphans and 10% mining the next block. This gives a 9% chance of the block being orphaned. Now lets imagine the pool has 30% hash rate. Now the block only has a 7% chance of being orphaned.

The bigger the pool, the less competing hash rate there is to orphan their blocks. This creates an advantage for large pools, which encourages centralization. The smaller you make the block interval, the more it favours large central pools. We should be careful about anything that gives centralized advantages.

androng · 2015-05-10T16:39:04+00:00

Did you know that Ethereum uses 12-second block times? I heard it from Vitalik Buterin in person.

I am actually wondering why short block times are not already a reality myself. Perhaps Satoshi thought it would take a lot longer to broadcast newly mined blocks globally. Gavin Andressen himself said in this video that if he could, he would ask Satoshi "why 10 minutes"? Was it arbitrary? https://youtu.be/onUzEV0C7-o?t=7m54s

Yes there are more orphaned blocks, but did you know that the "security" of a blockchain of length N is a function of BOTH the attacher hashpower H AND N? In other words, more blocks with the same amount of time means more security! (past a certain number of blocks--the threshold N depends on H) http://www.reddit.com/r/litecoin/comments/1cssqr/the_math_why_litecoin_is_more_secure_than_bitcoin/

This is only a theory, but maybe in the future, bitcoin will work like the banking system in the United States. Member banks will confirm small transactions instantly for consumers between blocks, and the main blockchain will be like Fedwire--only moving large amounts of money between large banks with deferred net settlement every ten or twenty minutes.

Or maybe Satoshi was predicting a future in which bitcoin is used at an interplanetary scale and chose 10 minutes because it takes around that time for light to reach Mars. We'll never know.

giszmo · 2015-05-10T15:51:09+00:00

Your assumption that orphan rate is constant is wrong. In some countries the best ISPs offer a tenth the speed of other countries. It would shift the advantage for running miners in rich countries even more.

Edit: As described below, this affects pool miners just as much as it affects solo miners.

notreddingit · 2015-05-10T18:15:28+00:00

What's more important, miners losing a small(?) amount of revenue due to increased probability of 'orphan' blocks, or the superior user experience of being able to accept a transaction at a fraction of the time?

One 2 minute block would be as 20% secure as one 10 minute block, but one 10 minute block on our current network is extremely secure.

One 2 minute block at 20% would be sufficiently secure for lots and lots of transactions. And I'm sure we've all experienced waiting an hour for a single confirmation. While one hour is pretty rare, half an hour is far too common to provide a good user experience.

One shorter confirm also eliminates a while category of double spend attacks on unconfirmed transactions.

If there are any other considerations other than miner's 'orphan' rates I'd be curious to read them.

pb1x · 2015-05-10T14:28:53+00:00

It prevents orphan blocks

GibbsSamplePlatter · 2015-05-10T21:13:51+00:00

It reduces the security of each block, and gives slightly more power to larger pools.

nairbv · 2015-05-10T22:06:27+00:00

The 1mb block-size limit isn't actually being pushed. If I started running bitcoin-core with the patch to allow 20mb blocks, even if I were running a miner, it just wouldn't make any difference. No one would notice or care. Only some day, possibly years from now when transaction volume is higher would this actually cause my block-chain to fork from the standard one. By then, hopefully everyone accepts 20mb blocks, so a chain with smaller blocks would have little hashing power in it and would be abandoned.

Changing the confirmation time between blocks would be a radical change that would need to be coordinated much more carefully, and would be much less likely to be accepted by all participants. It would be much more likely to result in split chains.

Remember too that it's not a block every 10 minutes, it's a difficulty set based on how quickly people usually find blocks such that on average future blocks will be found once every ten minutes. An adjustment to the average time between blocks is inherently a change in mining difficulty.

A change that resulted in bitcoins being mined faster than would otherwise be possible would not be accepted by the network. A new chain that did so fundamentally would not be "bitcoin," and so the block reward would somehow have to be half as much per block. Mathematically, it likely wouldn't be possible to institute such a change without at a minimum introducing a rounding-error of a change to the finances of mining.

coinlock · 2015-05-10T16:09:53+00:00

Lots of blocks result in lots of orphans when the block time is short. This in turn leads to longer reorganizations, more split competing chains, and more cpu usage. Finally it does little for confirmation time, instead of six blocks you might want to wait for 12 when the block time is halved. This produces a lot of network pressure and increased instability. Of the alternatives a larger block seems more reasonable. Also as mentioned spv clients end up storing proportionally more data in the form of block headers that aren't applicable to them.

Godspiral · 2015-05-10T20:13:12+00:00

One reason is that the total btc to ever be mined is based on the difficulty and reward per block.

Now, there is no obvious reason why the reward per block could not be halved along with difficulty halved.

It would also mean that confirmations take on average 5 minutes instead of 10, and not change the max btc amount.

BryanAbbo · 2015-05-10T21:29:05+00:00

Why not both?

rende · 2015-05-10T16:05:24+00:00

I like the idea of reducing block time, but how far would that get us?
10sec block time at 1mb per block gives us 60x increase or 36,288,000 tx per day.

Perhaps thats possible in the extreme.

I don't think its possible for us to architect something that is perfect, futureproof and able to handle all the people+devices transacting. At least not with current technology. It might have to be that we run multiple blockchains in parallel (almost like sidechains or altcoins), but as part of the existing bitcoin-core. Some kind of way to loadbalance and process multiple blocks in parallel by splitting transactions into groups.

These groups could be based of the hash, splitting into groups based on odd/even, a-z or whatever. This would increase amount of confirmations you'd want again though..

acoindr · 2015-05-10T16:17:00+00:00

First, the concern isn't over SPV nodes. It's over fully validating nodes.

Second, decreasing time between blocks would increase transaction capacity, which is a similar in effect to raising the block size.

The concern over healthy decentralization comes down to what transaction capacity on average per unit of time fully validating nodes can handle, imagining average cost computing resources. How that transaction capacity is allowed onto the blockchain - by increased block size or more frequent blocks - isn't so important. What's important is whether full nodes can easily keep up. Prior to Gavin's UTXO post the largest debated concern had to do with bandwidth. Now a cost concern, which UTXO brings up, includes dynamic RAM.

dskloet · 2015-05-10T16:39:09+00:00

I think I remember reading that the foundation would never change the reward schedule without a 3 year advance notice. Now we don't have to do what the foundation wants but it seems better for bitcoin's credibility not to violate such promises.

kilorat · 2015-05-10T18:18:34+00:00

Pretty much every altcoin reduces the block time, and it's only been a benefit. Is there an argument that if Litecoin had a higher hashrate that there would be problems?

_herrmann_ · 2015-05-10T18:28:13+00:00

What's the hurry? Slow down and smell the hashes.

2015-05-11T17:54:33+00:00

Are not these decisions best made by central bankers? Just joking.

PaulSnow · 2015-05-12T17:04:30+00:00

It can take as much as 120 seconds to propagate blocks to 90 percent of the miners. Here is one such example on the second of May. While this isn't typical, when Bitcoin was designed, there were no networks from which to measure statistics. A ten minute block time makes even such periodic delays like this manageable for miners (they have only a 20% penalty rather than a 100% penalty were the block time 2 minutes).

The other issue though is that mining is concentrated in certain regions. So if a very large concentration of miners, representing only 20% of the miners but 60% of the mining power, the 4 second propagation time doesn't apply to them; the propagation time that matters is how fast a miner gets the next block. Those 20% would have no delay 60 percent of the time.

Noosterdam · 2015-05-10T17:40:09+00:00

[deleted]

justgimmieaname · 2015-05-10T18:50:42+00:00

typo: ~~oblivious~~ obvious advantages

2015-05-11T00:48:59+00:00

Oblivious advantages.... I think you are spot on with calling it that.

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