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by brmunk 3439 days ago
You are absolutely right - the general problem is super hard. But even solving a specific use-case is hard for most developers who haven't done it before. It just takes a ton of time, and you often get some details wrong. And when you think you nailed it, then new requirements turns up :-) The result is that many apps don't work very well offline. That's why we have spent several man-years on making a general solution with sufficient flexibility to cover most use-cases. We want to enable all developers to be able to add offline first and real-time features without the hassle of reinventing the wheel every time.
1 comments
espadrine 3439 days ago
Another reason that OT is hard is that it doesn't fall out of a generic proof; you have to prove that your particular instance of OT follows a mathematical equation. And there is no tooling to verify that (it can't be ensured by typical type checkers).

So people either rely on an OT implementation that is generic enough for their needs, or risk inconsistency or subtle bugs to chase after for years.

Other approaches such as CRDT or total order are not vulnerable to that problem, but they have other concerns (like read performance, garbage collection, or intent preservation).

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simonask 3439 days ago
This is an interesting point. We at Realm have actually spent significant time thinking about it, and it is absolutely true that there is no easy way to prove the correctness of a system using OT.

But it helps to understand the fundamental constraints - for example, that operations must be commutative. In our case, we have had the luxury of designing our own database system, which means we could pick the semantics that we knew would lend themselves well to operational transformation. We have also made an effort to reuse semantics at multiple levels, limiting the number of OT instances that we had to convince ourselves would work.

Then of course, and for me at least, formal arguments are not enough, which is why we have spent a remarkable amount of resources on testing the system, including guided fuzz testing. :-)

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bsaul 3438 days ago
Some advice : if you want to have people trust and thus use this feature, you should make this kind of talk :

https://youtu.be/4fFDFbi3toc

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