7 ms·

> If the clock skew is only off by a few seconds or even minutes, the impact isn't so horrible, but if the clock jumps ahead by 20 years, you've effectively pre

> If the clock skew is only off by a few seconds or even minutes, the impact isn't so horrible, but if the clock jumps ahead by 20 years, you've effectively prevented any writes to that key for 20 years. That's true, but (luckily) it's easy to remediate those objects in the Roshi architecture. > If the UX impact [of lost writes] is negligible for you, that's great. One interesting thing that I've observed about this kind of data system work is that there seems to be a as-of-yet unsolvable tension between "general purpose applicability" and "specific purpose usability". That is, there isn't a way to design a CRDT-based causally-consistent data system which has a general purpose API that consumers can use for a suitably broad set of use cases. Instead, success stories like Roshi seem to require specializing both data semantics and APIs to the specific use cases they target. So, yes, if someone can't tolerate/remediate lost writes due to clock drift, then Roshi is not a suitable system. But, that's fine: data systems don't have to be general purpose to be useful, or to advance the state of the art.

marknadal 7y ago
General purpose CRDTs have been available for at least 5+ years. We have such a system ( http://github.com/amark/gun http://github.com/amark/gun ) that is running in production at the Internet Archive, and P2P versions of Reddit & YouTube that have ~2M users. Dealing with this UX stuff is very important, and we have distributed systems correctness tests (https://github.com/gundb/panic-server https://github.com/gundb/panic-server) that does split brain simulation and recovery, and code to handle timestamp skew even if NTP is running. If you pass this off to developers to be responsible for, they won't know the difference between mistakes in your system and mistakes in theirs. They shouldn't need to be a distributed systems expert to use the database.
specialist 7y ago
I'm really digging this thread. Nicely done. Thanks. As a noob, some kind of Starting Assumptions and Context would be cool for all these distributed infra projects. For instance, I wouldn't have known about mitigating time skews in data centers. Or perhaps even a reference deployment, image(s), playbook, or whatever the devops people are now calling it.

marknadal 7y ago

General purpose CRDTs have been available for at least 5+ years. We have such a system ( http://github.com/amark/gun http://github.com/amark/gun ) that is running in production at the Internet Archive, and P2P versions of Reddit & YouTube that have ~2M users. Dealing with this UX stuff is very important, and we have distributed systems correctness tests (https://github.com/gundb/panic-server https://github.com/gundb/panic-server) that does split brain simulation and recovery, and code to handle timestamp skew even if NTP is running. If you pass this off to developers to be responsible for, they won't know the difference between mistakes in your system and mistakes in theirs. They shouldn't need to be a distributed systems expert to use the database.

specialist 7y ago

I'm really digging this thread. Nicely done. Thanks. As a noob, some kind of Starting Assumptions and Context would be cool for all these distributed infra projects. For instance, I wouldn't have known about mitigating time skews in data centers. Or perhaps even a reference deployment, image(s), playbook, or whatever the devops people are now calling it.