There are even enterprise-ready setups using CouchDB (like Cloudant) for those that want it.
There’s tons of stuff CouchDB sync doesn’t support that end up being a huge problem with mobile apps… Here are the top 3 things Realm adds in my opinion: great client-side performance, native models that are extremely easy to use, and conflict-free sync (not conflict resolution!). With my own eyes I’ve seen a generation of developers try CouchDB for mobile apps and then abandon it because of the limitation of its approach. Personally I’m glad to see someone try to bring more options to developers. I think this is the first general-case true sync (à la Google Docs) for mobile, and I hope it will continue to spur more iterations & innovation in other open-source projects as well.
You lay it out there and then talk about what Realm adds, but never what Couch lacks. And are you including PouchDB in your evaluation of CouchDB for "Client-Side Performance"?
As I understand PouchDB is performant, uses JSON (pretty much the definition of "Native Models"), and allows server-arbitrated conflict resolution with stored revisions, making the simplest conflict resolution "last-in-wins" with user UI for "undo" (or any JS-object merge library).
Thanks!
I'm deeply relieved to see that they're launching something that does something about the fragile ios architectures built around JSON. It's similar to what they did with their mobile database: they actually listened to what mobile devs found annoying, and then they built something that completely sidestepped all the fragility problems that emerge when you wrap sqlite with an ORM. Instead, they made an approach that fit within our workflow, as opposed to taking us further from it.
Thanks for listing those potential benefits. Any idea if those CouchDB issues are covered in detail somewhere?
"great client-side performance": PouchDB is more than fast enough for most use cases, its just a wrapper over indexedDB. (there are areas we can improve, particularly performance of map reduce / mango queries).
"native models that are extremely easy to use": Not sure what that means, PouchDB and CouchDB use json, its native and easy to use in JavaScript
"conflict-free sync (not conflict resolution!)": Certainly going to have to take a look at this, any conflict free sync protocol I have seen put a lot of limitations on how data within your application is structured but conflict resolution certainly is something that can be improved within Pouch / Couch.
I do think there is a bunch we can (and are) improving in PouchDB and its great to see alternatives, will be looking into this further now. But I certainly do not agree that (C|P)ouchDB are not suited for mobile <-> web sync, thats the primary use case I work on Pouch for.
For "conflict-free sync," according to the docs, this appears to be last-write-wins along with a special case for deletes: https://realm.io/docs/realm-object-server/#conflict-resoluti... . (Incidentally Couch/Pouch also has a special case for deletes, but it does the opposite behavior by default – deletions lose to updates.)
There's also some language in here about how "insertions in lists are ordered by time;" I'd be curious to know how they coordinate clock times across nodes. Ditto for "last update wins" – important to know how "last" is determined.
In general, I tend to be skeptical of systems that hinge on last-write-wins, but LWW is definitely a model that works in a lot of cases where you're not too concerned about the possibility of losing data, and it's also a simpler mental model for the app developer.
This essentially means that the entire object graph is treated as one big CRDT [0], transparently handling conflict across individual objects, properties and relations.
When talking about ordering by time, both in the context of LWW and insertions in lists, we are talking about vector clock time, not necessarily device time (or though that is taken into account as well).
[0] https://en.wikipedia.org/wiki/Conflict-free_replicated_data_...
While reading the announce, my first guess was some recursive per-field LWW, but you mentioned vector clocks. That is intriguing.
This means native code (specifically not JSON). So in Java you would be dealing with POJOs, etc...
I'm happy to learn about a silver bullet here.
It's a fair trade-off, but hardly neither objectively worse or better than couch-sync. I'm excited to see where Realm goes.
In my very unscientific approximation couch/git-style sync solves about 80% of general use cases, CRDT/OT cover another 10-15% and the rest are poor souls that have to do something custom. (All this excluding binary sync/rsync/BitTorrent/Dropbox.)