One implementation of it, google's, uses leveldb:
https://github.com/google/certificate-transparency
Another one out there uses postgres. It turns out that you can use traditional databases in many cases where you think you need a blockchain, and you'll be able to waste vastly less energy on proof-of-work and vastly less time dealing with the terrible mess that is "blockchain".
The reason not to use "blockchain" is that it has 200 definitions, all of them full of people trying to get rich, not getting things done.
Databases have long-since solved the problem of storing and distributing data.
Distributed stores like etcd, zookeeper, and so on have long since solved the problem of duplicating data.
Very few people need byzentine fault tolerance (due to having a large number of untrusted actors with write access), which is the only time the additional complexity blockchain includes is actually useful
Hence we shall issue signed receipts to all clients and providers then setup a system to pay out a large bounty if someone can produce a signed receipt not in our weekly-published-log. We'll automate the bounty, but perhaps a third party will also offer a validator. We will not even need Postgres for it, just nginx and a filesystem.
But that is not interesting enough by itself, and mentioning digital signatures just confuses people more. So we call it a Single-Issuer-Blockchain: Now people instantly get the idea.
In my case, this sentiment accompanies an implementation in the form of an easily-deployable open source microservice.
https://github.com/paragonie/chronicle
If it's too hard for people to build, they can use what I wrote.
> What is this hypothetical non-blockchain, where are you going to get it, and why not just use a blockchain if that's what you need?
That's the tx/s limit on Bitcoin today? I can do hundreds of writes per seconds to Chronicle on a modest VM without sweat. This is possible because it's centralized, albeit supports mirroring (i.e. replication) and cross-signing.
...
Are people still fighting about this or have they come to a consensus?
I'm probably the worst person to represent whether there's a consensus or not since I'm one of the designers of Ripple. But the important thing, at least in my opinion, is that there is no "secret sauce".
The software is open source. People are free to modify it however they please. We run the exact same software that we make available on our public servers and our validators. Others are free to run validators and they do so.
As it happens, much of the network infrastructure is run by us today. But we are more than happy to turn that over to others who are willing to do it.
Why do you care if something is decentralized? The main reason is usually that you don't want the users of the system to be forced to accept changes made by an owner/operator of the system whose interest may be averse to them. Ripple is decentralized in this sense.
For example, eBay is not decentralized. They don't warehouse their goods. But if eBay the company says no auctions of adult merchandise, then there will be no such auctions. It wouldn't matter if every user disagreed with the policy. Their only recourse would be to re-create what eBay had done, that is, to themselves implement eBay's secret sauce.
By contrast, Ripple has no secret sauce. Anyone can run their own servers. If we make changes people don't like, nothing requires them to run the code with those changes. If Ripple disappeared and users of the ledger wanted it to continue, nothing would stop them from continuing it.
https://bitcoin.stackexchange.com/questions/40448/is-ripple-...
It's way more like Certificate Transparency than Ripple. Chronicle has nothing to do with payments or currency. It's just a ledger.