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Comment by nupark2 | Hacker News Reader

The problems on mobile are so incredibly different than server, I don't see that CouchDB would be useful client-side.

The focus client-side is on speed, battery-life, ease of programming, and perhaps most of all, maintaining separation of concerns between the server-side data model and the client data model. The server must be free to evolve independently of the client, and many remote clients will run legacy versions of your software for extended periods of time.

Moreover, rarely is data distribution sufficient to model high-level interactions between client and server, which is more likely to introduce bugs, complexity, and significantly detract from the long-term maintainability of the client/server protocol.

The end result is that you don't particularly benefit from CouchDB client-side, and especially not replication -- you need a well-defined supportable network model.

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Speed, battery-life, ease of programming are 3 of the main reasons we are motivated to build a Couch-compatible storage and sync layer on the device. If you have an intelligent sync solution, you can use significantly less radio time to present the same features. This saves battery life, and gives a better user experience as folks aren't waiting for hundreds of milliseconds for request and response to propagate across unreliable mobile networks.

As far as the maintainability concerns, it's an interesting point. There are certainly apps which may want to sacrifice the ease of use and performance advantages of having sync done for you, because they have specialized data sharing requirements.

But for a whole lot of apps the benefits of sync far outweigh the contraints of having the same data model on the client and server.

Some example use cases where sync can simplify programming (or even make a class of apps possible which would be much harder without it): point-of-sale, retail, medical records (doctor with an iPad and limited wifi), military (need that data no matter what).

Here's a pdf of the slides I presented yesterday at Chicago's WindyCityGo conference: http://dl.dropbox.com/u/14074521/syncpoint-windycity-small.p...

> Speed, battery-life, ease of programming are 3 of the main reasons we are motivated to build a Couch-compatible storage and sync layer on the device. If you have an intelligent sync solution, you can use significantly less radio time to present the same features.

You're just moving the costs around, and likely transmitting far more data than needs be sent.

In addition, you're front-loading the transmission of data that users don't need right now.

Having built many network-facing mobile applications with exceedingly large user bases, I'm unconvinced. The maintenance complexity, the excess transmission of data, issues of data consistency over time, the lack of integration with client-side business rules without considerable investment in code that significantly replaces the sync logic.

I think that the reality of the situation is that in the rare cases you need offline, fully synchronized data, it's not particularly difficult to just download what you need as an atomic unit and save it. The majority of the time, however, on-demand request handling is more efficient, well-defined, and maintainable.

For use cases where it's very important that users be able to read (and write) regardless of connection status, it makes a huge difference to have transparent sync.

As far as ease of writing apps (and maintaining them), time will tell, some of our users have been at it for a few years now. The things I've seen people do, show me the synchronizing document model works.

[edit] To be clear - Couchbase Server is mostly used for the explicit network model you advocate. For instance, the OMG POP mobile success story is using Couchbase as regular backend database storage.

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