[aerogear-dev] Offline and Sync Brainstorm

Wed Apr 10 05:23:38 EDT 2013

On Wed, Mar 27, 2013 at 7:43 PM, 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.
>
> IMO, because Aerogear is a library we should focus on a Transactional sync
to let the users a more fine-grained control. But later, we should be able
to provide some wrappers around this atomic operations to offer something
close to document sync (or let the users easily define a "Document", like a
view in SQL)

> 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?
>

Shouldn't we trigger a sync only when we go from an offline status to an
online status ? And sync strategy should be configurable (both on client
side and server side)

>
> 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?
>

Yes, we should promote push but have a fallback to a pull strategy

>
> 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
>

I would add another option :
E. The Strongest always win : i.e An admin user change will always be
considered with a higher weight when merging a conflict.

>
> 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.
>

Ideally, we should be able to provide the same functionality no matter we
are online or offline. For example, when I'm in the middle of the ocean, I
still want to be able to tag my Dolphins ;)
But we could think about "degraded service levels" ...

>
> 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?
>

We could take a look at the Grails html5-scaffolding plugin which cover
some of this use cases
https://github.com/3musket33rs/html5-mobile-scaffolding

>
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