It's also amazing how much you can fit in RAM if you're careful. I remember ~2007 people were aghast at Facebook's 4T memcached deployment that stored basically everyone's social network posts; now you can get single servers for ~$4K with 4T of RAM.
The trick is basically that you have to eschew the last 15 years of "productivity" enhancements. Pretty much any dynamic language is out; if you must use the JVM or .NET, store as much as possible in flat buffers of primitive types. I ended up converting order books from the obvious representation (hashtable mapping prices to a list of Order structs) to a pair of SortedMaps from FastUtils, which provides an unboxed float representation with no pointers. That change ended up reducing memory usage by about 4x.
You can fit a lot of ints and floats in today's 100G+ machines, way more than needed to represent the entire cryptocurrency market. You just can't do that when you're chasing 3 pointers, each with their associated object headers, to store 4 bytes.
The more I read comments on subjects I am intimately familiar with, the more I realize most people who comment on HN don't really know what they're talking about and mostly make things up.
To answer your question, you can't find these servers because they don't exist. A server with 4T of RAM will cost you at a minimum $20,000 and that will be for some really crappy low-grade RAM. Realistically for an actual server that one would use in an actual semi-production setting, you're looking at a minimum of $35,000 for 4TB of RAM and that's just for the RAM alone, although to be fair that 35k ends up dominating the cost of the entire system.
> the more I realize most people who comment on HN don't really know what they're talking about and mostly make things up.
I don't think they're typically making things up. It's what I prefer to call Reddit knowledge. They saw someone else claim it somewhere, they believed it, and so they're repeating it so they can be part of the conversation (people like to belong, like to be part of, like to join). It's an extremely common process on Reddit and most forums, and HN isn't immune to it. Most people don't read much and don't acquire most of their knowledge from high quality sources, their (thought to be correct) wider knowledge - on diverse topics they have no specialization on - is frequently acquired from what other people say and that they believe. So they flip around on Reddit or Twitter for a bit, digest a few nuggets of questionable 'knowledge' and then regurgitate it at some later point, in a process of wanting to participate and belong socially. It's how political talking points function for example, passed down to mimic distributors that spread the gospel to other mimic followers (usually without questioning). It's how religion functions. And it's how most teachers / teaching functions, the teachers are distribution mimics (mimics with a bullhorn, granted authority by other mimics to keep the system going, to clone).
It's because some very high percentage of all of humans are mimics. It's not something Reddit caused of course, it's biology, it's a behavior that has always been part of humanity. It's an increased odds of success method of optimizing for survival of the species, successful outcomes, meets the Internet age. It's why most people are inherent followers, and can never be (nor desire to be) leaders. It's why few people create anything original or even attempt to across a lifetime. It's why such a small fraction of the population are very artistic, particularly drawn to that level of creative expression. If you're a mimic biologically it's very difficult to be the opposite. This seems to be viewed by most people as an insult (understandably, as mimics are the vast majority of the population and control the vote), however it's not, it's simply how most living things function, system wise, by mimicry (or even more direct forms of copying). Humans aren't that special, we're not entirely distinct from all the other systems of animal behavior.
That saying, safety in numbers? That's what that is all about. Mimicry. Don't stand out.
The reason most Wall Street money managers can't beat the S&P 500? It's because they're particularly aggressive mimics, they intentionally copy eachother toward safe, very prosperous, gentle mediocrity. They play a game of follow, with popular trends (each decade or era on Wall Street has popular trends/fads). Don't drift too far below the other mimics and it's a golden ticket.
Nobody got fired for buying IBM? Same thing. Mimic what has worked well for many others is biologically typically a high success outcome pattern (although amusingly not always, it can also in rare occasions lead off a cliff).
The Taliban? The Soviet Union? Nazism? Genocide? Multi generational patterns of mistake repetition passed down from parental units? That's how you get that. People mimic (perhaps especially parental units; biology very much in action), even in cases where it's an unsuccessful/negative pattern. All bad (and good) ideologies have mimic distributors and mimic followers, the followers do what they're told and implement as they're told. And usually there are only a very small number of originators, which is where the mimic distributors get their material.
The concept of positive role models? It's about mimicry toward successful outcomes.
Being a mimic and being a leader/creator are not exclusive; you can do both in various fields. One can even mimic and eventually start creating their own things on the back of that: “fake it until you make it” is a real thing.
> The more I read comments on subjects I am intimately familiar with, the more I realize most people who comment on HN don't really know what they're talking about and mostly make things up.
HN doesn't look exactly like SlashDot, but it's absolutely just like SlashDot.
I just Googled [servers with 4T of RAM], but apparently no, it does not include the RAM itself. Came up with this (about $4K base, another $44K to max it out with RAM):
Yeah, I've been eyeing the EPYC servers, but RAM pricing seems to very roughly be in the ballpark of $1,000 for 128GB, so $4k for 4T sounded very attractive and I wanted to make sure that I wasn't missing anything. As
cvwright pointed out, you can get old DDR3 RAM for less, but I haven't found servers that can fit that many DIMMs. Thanks for your response.
I'm fairly sure I know where I can buy used/refurb Dell R820 at good prices with 512 or 1024GB of RAM, but I don't think I could accomplish the same for 4TB of RAM and $4000. Certainly not in one machine. And not with two $2000 machines each with 2048MB. We're close, but it's not that cheap yet.
Looking on ebay I can find some pretty decent R820 with 512GB each for right around $1500 a piece. Not counting any storage, even if they come used with some spinning hard drives, would end up replacing with SSDs. So more like three servers, 1.5TB of RAM, for $4500.
Yeah I run mirrors for certain sites in different regions of the world and a trick I often do is scrape the target site and then hold the entire site in memory. Even the top 500 posts of HN and all of the associated comments can fit in < 16 MB of RAM. If you want to serve that up over a socket, it's really fast to grab a pointer to the memory and just write it to the socket. You can get response times which are dwarfed by network latency that way.
The trick is basically that you have to eschew the last 15 years of "productivity" enhancements. Pretty much any dynamic language is out; if you must use the JVM or .NET, store as much as possible in flat buffers of primitive types. I ended up converting order books from the obvious representation (hashtable mapping prices to a list of Order structs) to a pair of SortedMaps from FastUtils, which provides an unboxed float representation with no pointers. That change ended up reducing memory usage by about 4x.
You can fit a lot of ints and floats in today's 100G+ machines, way more than needed to represent the entire cryptocurrency market. You just can't do that when you're chasing 3 pointers, each with their associated object headers, to store 4 bytes.