[aerogear-dev] Offline and Sync Brainstorm

[Rodney Russ]

FYI ... I know Mike has been planning to implement Operation Transforms (Eventual Consistency) in the 3.0 release of Errai.  It may be worth looking at whether there is something that can be shared from this as I know he had been considering working on this with the Infinspan team.

----- "Summers Pittman" <supittma at redhat.com> wrote:

> Sorry for the questionable formatting before, this should be more 
> correct now.
> 
> So for offline and sync for 2.0 I’ve been doing some thinking/research
> 
> and come up with some broad topics to discuss so we can start honing
> in 
> on what we want it to do/look like.
> 
> This isn’t a spec, this isn’t a proposal, this is just trying to
> narrow 
> down what we want at a high level so we can pick things to focus on.
> 
> 1. Documents vs Transactions
> 
> There are two “big picture” methods of doing sync. One is a Document 
> sync (Think like a gallery with videos and pictures). Documents are 
> saved, the whole document is sent to the server, then the whole
> document 
> is pushed out to other clients who are syncing against the same
> source. 
> The other is a Transactional sync where many small atomic operations
> are 
> sent to the server. The best analog I have is Google Drive/operation 
> transforms.
> 
> Obviously the server side implementations of these are hilariously 
> divergent and I will leave the relative complexity of each as an 
> exercise for the list.
> 
> 2. Background vs Foreground sync
> 
> Does the application have to be opened (foreground) for syncing to 
> happen? As far as I know, native Web requires this (barring extensions
> 
> to the browser, plugins etc). I think Cordova can in Android, but I 
> haven’t researched it. iOS seems like a mixed bag, but generally you
> can 
> only sync if your application is in the foreground (but you can use 
> notifications and badges to communicate that there is a pending sync
> or 
> new data). I understand there is CoreData + iCloud that is supposed to
> 
> do something, but that seems like it is still foreground only. On 
> Android background sync is easy.
> 
> Is it OK to only have background syncing on some platforms but not
> others?
> 
> 3. Push vs Poll?
> 
> Obviously pushing updates is better for devices and users, but polling
> 
> will let things work better for legacy services which may not have
> push 
> support or which may be difficult to integrate into AG-Controller.
> 
> Should we support both on the clients?
> 
> 4. Multiple clients,multiple users, and conflicts
> 
> How do we want to support multiple users and multiple clients? How 
> should we try to do conflict resolution? What does authorization and 
> authentication look like here?
> 
> At a high level here are some options I have seen for conflict
> resolution:
> 
> A. Last in always wins. The server explicitly trusts things in the
> order 
> it gets and pushes that data out to users.
> 
> B. Clients are allowed one submit at a time and must wait for the
> server 
> to acknowledge the receipt. If there is a conflict the app can either
> a) 
> merge the data, b)reload the latest from the server and make the user
> do 
> his operation again, or c) create a new document and inform the user.
> 
> C. Operation Transforms. This was meant to solve the conflict and sync
> 
> problem. However it is a LOT of work
> 
> 5. Offline Support
> 
> Really this is more what do we want to do for coming from an “offline”
> 
> mode to an “online” mode? Abstractly, operations which happen offline
> 
> are the same as operations which happen online just with a REALLY
> REALLY 
> laggy connection. :) We could just only viewing data when offline and
> 
> requiring a connection for editing, queueing an upload, etc.
> 
> 6. How much of this is the responsibility of AG-controller vs
> underlying 
> services?
> 
> How should the controller expose resources to clients, how should the
> 
> controller send data to its underlying services, how much data should
> 
> the controller be responsible itself for?
> 
> Should it be easy for an Operation Transform system to integrate with
> 
> AeroGear-controller?
> Should it be easy to write a Controller based project which polls a 
> third party source?
> How would the server handle passing credentials to the third party
> source?
> 
> Appendix Use Cases:
> 
> Here are a few contrived use cases that we may want to keep in mind.
> 
> 1. Legacy Bug Trackers From Hell
> a. It is a webapp written in COBOL, no one will ever EVER update or 
> change the code
> b. It has TONS of legacy but important data
> c. It has TONS of users
> d. It only has a few transactions per day, all creating and updating
> bug 
> reports
> e. Multiple users can edit the same report
> 
> 2. Slacker Gallery
> a. Each User has a multiple galleries, each gallery has multiple
> photos
> b. A Gallery has only one user, but the user may be on multiple
> devices
> c. Galleries may be renamed, created, and deleted
> d. Photos may only be created or deleted. Photos also have meta data 
> which may be updated, but its creation and deletion is tied to the
> Photo 
> object.
> 
> 3. Dropbox clone
> a. A folder of files may be shared among users
> b. There is a size limit to files and how much storage may be used per
> 
> folder
> c. Files are not updated. If there is a new file, there is an atomic 
> delete and create operation
> 
> 4. Email client
> a. This is an AG-controller which accesses a mail account.
> b. There are mobile offline and sync enabled clients which connect to
> 
> this controller.
> 
> 5. Google Docs clone
> a. Operational Transform out the wazzoo
> b. What would the server need?
> c. What would the client need?
> 
> Appendix Reference (Open Source) Products:
> 
> Wave-in-a-box
> CouchDB
> Google Drive RealtimeAPI
> share.js
> etherpad
> 
> Can you guys think of more projects/examples to look at for
> inspiration?
> 
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