> So your cluster isn't going to need to plan to handle 15k transactions per > second, you're really looking at more like 200k or even 500k transactions per > second to handle peak-volumes. And if it can't, you're still going to see > full blocks.
When I first began to enter the blocksize debate slime-trap that we have all found ourselves in, I had the same line of reasoning that you have now. It is clearly untenable that blockchains are an incredibly inefficient and poorly designed system for massive scales of transactions, as I'm sure you would agree. Therefore, I felt it was an important point for people to accept this reality now and stop trying to use Blockchains for things they weren't good for, as much for their own good as anyone elses. I backed this by calculating some miner fee requirements as well as the very issue you raised. A few people argued with me rationally, and gradually I was forced to look at a different question: Granted that we cannot fit all desired transactions on a blockchain, how many CAN we effectively fit? It took another month before I actually changed my mind. What changed it was when I tried to make estimations, assuming all the reasonable trends I could find held, about future transaction fees and future node costs. Did they need to go up exponentially? How fast, what would we be dealing with in the future? After seeing the huge divergence in node operational costs without size increases($3 vs $3000 after some number of years stands out in my memory), I tried to adjust various things, until I started comparing the costs in BTC terms. I eventually realized that comparing node operational costs in BTC per unit time versus transaction costs in dollars revealed that node operational costs per unit time could decrease without causing transaction fees to rise. The transaction fees still had to hit $1 or $2, sometimes $4, to remain a viable protection, but otherwise they could become stable around those points and node operational costs per unit time still decreased. None of that may mean anything to you, so you may ignore it all if you like, but my point in all of that is that I once used similar logic, but any disagreements we may have does not mean I magically think as you implied above. Some people think blockchains should fit any transaction of any size, and I'm sure you and I would both agree that's ridiculous. Blocks will nearly always be full in the future. There is no need to attempt to handle unusual volume increases - The fee markets will balance it and the use-cases that can barely afford to fit on-chain will simply have to wait for awhile. The question is not "can we handle all traffic," it is "how many use-cases can we enable without sacrificing our most essential features?" (And for that matter, what is each essential feature, and what is it worth?) There are many distinct cut-off points that we could consider. On the extreme end, Raspberry Pi's and toasters are out. Data-bound mobile phones are out for at least the next few years if ever. Currently the concern is around home user bandwidth limits. The next limit after that may either be the CPU, memory, or bandwidth of a single top-end PC. The limit after that may be the highest dataspeeds that large, remote Bitcoin mining facilities are able to afford, but after fees rise and a few years, they may remove that limit for us. Then the next limit might be on the maximum amount of memory available within a single datacenter server. At each limit we consider, we have a choice of killing off a number of on-chain usecases versus the cost of losing the nodes who can't reach the next limit effectively. I have my inclinations about where the limits would be best set, but the reality is I don't know the numbers on the vulnerability and security risks associated with various node distributions. I'd really like to, because if I did I could begin evaluating the costs on each side. > How much RAM do you need to process blocks like that? That's a good question, and one I don't have a good handle on. How does Bitcoin's current memory usage scale? It can't be based on the UTXO, which is 1.7 GB while my node is only using ~450mb of ram. How does ram consumption increase with a large block versus small ones? Are there trade-offs that can be made to write to disk if ram usage grew too large? If that proved to be a prohibitively large growth number, that becomes a worthwhile number to consider for scaling. Of note, you can currently buy EC2 instances with 256gb of ram easily, and in 14 years that will be even higher. > So you have to rework the code to operate on a computer cluster. I believe this is exactly the kind of discussion we should be having 14 years before it might be needed. Also, this wouldn't be unique - Some software I have used in the past (graphite metric collection) came pre-packaged with the ability to scale out to multiple machines split loads and replicate the data, and so could future node software. > Further, are storage costs consistent when we're talking about setting up > clusters? Are bandwidth costs consistent when we're talking about setting up > clusters? Are RAM and CPU costs consistent when we're talking about setting > up clusters? No, they aren't. Bandwidth costs are, as intra-datacenter bandwidth is generally free. The other ones warrant evaluation for the distant future. I would expect that CPU resources is the first thing we would have to change - 13 thousand transactions per second is an awful lot to process. I'm not intimately familiar with the processing - Isn't it largely signature verification of the transaction itself, plus a minority of time spent checking and updating utxo values, and finally a small number of hashes to check block validity? If signature verification was controlling, a specialized asic chip(on a plug-in card) might be able to verify signatures hundreds of times faster, and it could even be on a cheap 130nm chipset like the first asic miners rushed to market. Point being, there are options and it may warrant looking into after the risk to node reductions. > You'd need a handful of experts just to maintain such a thing. I don't think this is as big a deal as it first might seem. The software would already come written to be spanned onto multiple machines - it just needs to be configured. For the specific question at hand, the exchange would already have IT staff and datacenter capacity/operations for their other operations. In the more general case, the numbers involved don't work out to extreme concerns at that level. The highest cpu usage I've observed on my nodes is less than 5%, less than 1% for the time I just checked, handling ~3 tx/s. So being conservative, if it hits 100% on one core at 60-120 tx/s, that works out to ~25-50 8-core machines. But again, that's a 2-year old laptop CPU and we're talking about 14 years into the future. Even if it was 25 machines, that's the kind of operation a one or two man IT team just runs on the side with their extra duties. It isn't enough to hire a fulltime tech for. > Disks are going to be failing every day when you are storing multiple PB, so > you can't just count a flat cost of $20/TB and expect that to work. I mean, that's literally what Amazon does for you with S3, which was even cheaper than the EBS datastore pricing I was looking at. So.... Even disregarding that, raid operation was a solved thing more than 10 years ago, and hard drives 14 years out would be roughly ~110 TB for a $240 hard drive at a 14%/year growth rate. In 2034 the blockchain would fit on 10 of those. Not exactly a "failing every day" kind of problem. By 2040, you'd need *gasp* 22 $240 hard drives. I mean, it is a lot, but not a lot like you're implying. > And you need a way to rebuild everything without taking the system offline. That depends heavily upon the tradeoffs the businesses can make. I don't think node operation at an exchange is a five-nines uptime operation. They could probably tolerate 3 nines. The worst that happens is occasionally people's withdrawals and deposit are delayed slightly. It won't shut down trading. > I'm sure there are a dozen other significant issues that one of the Visa > architects could tell you about when dealing with mission-critical data at > this scale. Visa stores the only copy. They can't afford to lose the data. Bitcoin isn't like that, as others pointed out. And for most businesses, if their node must be rebooted periodically, it isn't a huge deal. > Once we grow the blocksize large enough that a single computer can't do all > the processing all by itself we get into a world of much harder, much more > expensive scaling problems. Ok, when is that point, and what is the tradeoff in terms of nodes? Just because something is hard doesn't mean it isn't worth doing. That's just a defeatist attitude. How big can we get, for what tradeoffs, and what do we need to do to get there? > You have to check each transaction against each other transaction to make > sure that they aren't double spending eachother. This is really not that hard. Have a central database, update/check the utxo values in block-store increments. If a utxo has already been used this increment, the block is invalid. If the database somehow got too big(not going to happen at these scales, but if it did), it can be sharded trivially on the transaction information. These are solved problems, the free database software that's available is pretty powerful. > You have to be a lot more clever than that to get things working and > consistent. NO, NOT CLEVER. WE CAN'T DO THAT. Sorry, I had to. :) > None of them have cost structures in the 6 digit range, and I'd bet (without > actually knowing) that none of them have cost structures in the 7 digit range > either. I know of and have experience working with systems that handled several orders of magnitude more data than this. None of the issues brought up above are problems that someone hasn't solved. Transaction commitments to databases? Data consistency across multiple workers? Data storage measured in exabytes? Data storage and updates approaching hundreds of millions of datapoints per second? These things are done every single day at numerous companies. On Fri, Mar 31, 2017 at 11:23 AM, David Vorick <david.vor...@gmail.com> wrote: > Sure, your math is pretty much entirely irrelevant because scaling systems > to massive sizes doesn't work that way. > > At 400B transactions per year we're looking at block sizes of 4.5 GB, and a > database size of petabytes. How much RAM do you need to process blocks like > that? Can you fit that much RAM into a single machine? Okay, you can't fit > that much RAM into a single machine. So you have to rework the code to > operate on a computer cluster. > > Already we've hit a significant problem. You aren't going to rewrite Bitcoin > to do block validation on a computer cluster overnight. Further, are storage > costs consistent when we're talking about setting up clusters? Are bandwidth > costs consistent when we're talking about setting up clusters? Are RAM and > CPU costs consistent when we're talking about setting up clusters? No, they > aren't. Clusters are a lot more expensive to set up per-resource because > they need to talk to eachother and synchronize with eachother and you have a > LOT more parts, so you have to build in redundancies that aren't necessary > in non-clusters. > > Also worth pointing out that peak transaction volumes are typically 20-50x > the size of typical transaction volumes. So your cluster isn't going to need > to plan to handle 15k transactions per second, you're really looking at more > like 200k or even 500k transactions per second to handle peak-volumes. And > if it can't, you're still going to see full blocks. > > You'd need a handful of experts just to maintain such a thing. Disks are > going to be failing every day when you are storing multiple PB, so you can't > just count a flat cost of $20/TB and expect that to work. You're going to > need redundancy and tolerance so that you don't lose the system when a few > of your hard drives all fail within minutes of eachother. And you need a way > to rebuild everything without taking the system offline. > > This isn't even my area of expertise. I'm sure there are a dozen other > significant issues that one of the Visa architects could tell you about when > dealing with mission-critical data at this scale. > > -------- > > Massive systems operate very differently and are much more costly per-unit > than tiny systems. Once we grow the blocksize large enough that a single > computer can't do all the processing all by itself we get into a world of > much harder, much more expensive scaling problems. Especially because we're > talking about a distributed system where the nodes don't even trust each > other. And transaction processing is largely non-parallel. You have to check > each transaction against each other transaction to make sure that they > aren't double spending eachother. This takes synchronization and prevents > 500 CPUs from all crunching the data concurrently. You have to be a lot more > clever than that to get things working and consistent. > > When talking about scalability problems, you should ask yourself what other > systems in the world operate at the scales you are talking about. None of > them have cost structures in the 6 digit range, and I'd bet (without > actually knowing) that none of them have cost structures in the 7 digit > range either. In fact I know from working in a related industry that the > cost structures for the datacenters (plus the support engineers, plus the > software management, etc.) that do airline ticket processing are above $5 > million per year for the larger airlines. Visa is probably even more > expensive than that (though I can only speculate). _______________________________________________ bitcoin-dev mailing list bitcoin-dev@lists.linuxfoundation.org https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev
