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Comment by crdrost | Hacker News Reader

There's a whole database, Datomic, that works roughly this way -- not the UDP multicast but the idea of having a slightly more nuanced consistency/availability/partition tolerance tradeoff by having a thin transaction organizer which is not partition tolerant and officially states which one came first and second, upstream of the replicas that grant normal availability.

I would have liked the discussion about Raft/Paxos that they said they'd leave out of this episode though :(

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CORFU and Tango are interesting research implementations in this general area, with emphasis on a dedicated "sequencer" - see https://rebeccabilbro.github.io/the-shared-log-abstraction/

Facebook's LogDevice had a similar sequencer component too https://engineering.fb.com/2017/08/31/core-data/logdevice-a-...

Yeah, and the key idea here is that the sequencer is soft state that can be recovered from the log at any time. It acts to improve throughput while it's up, but if it's down the system can still make progress. The key to this is that the log is the ultimate ground source of truth, and individual entries in the log are write once. This means racing writers can detect and work around each other in the absence of a sequencer, via the hole filling protocol.

FaunaDB (fauna.com) is a commercial system based on Calvin.

Disclosure: I work on FaunaDB.

Sounds similar to xtdb

https://github.com/xtdb/xtdb

Yeah as I understand it XTDB was built by Juxt after using Datomic for a long while, to make a different set of trade-off choices.

Whenever one comes up, the other is likely to be mentioned close at hand:

https://docs.xtdb.com/resources/faq/#comparisons

What's the state of Datomic these days? I stopped keeping up with it a while back when I stopped really paying attention to the Clojure space in general. Last I remember hearing it was still a purely pay to use their instances sort of deal.

> What's the state of Datomic these days?

Continuous, minor improvements over time (just like Clojure). Nothing too groundbreaking lately AFAIK, but still worthy to use if you have the use cases for it. Changelog can be found here: https://docs.datomic.com/on-prem/changes.html

There's on-prem which is the original model, and then the newer Datomic Cloud (came about in ~2018) which is installed from AWS Marketplace and billed through AWS. There are some feature differences between them. With on-prem there are free and $$ licensing options. Might be that the on-prem gratis licensing options were more limited before.

Some of the cool kids in Clojure world seem to have moved over to XTDB these days.

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