[aerogear-dev] Offline and Sync Brainstorm

Wed Apr 10 09:30:26 EDT 2013

On Wed, Apr 10, 2013 at 3:00 PM, Summers Pittman <supittma at redhat.com>wrote:

>  On 04/10/2013 05:23 AM, Sebastien Blanc wrote:
>
>
>
>
> 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 ?
>
> No.  The only difference (conceptually) between being online and offline
> is latency.
>
> If I am polling (yuck) ever 5 minutes and I am offline for two of those
> minutes, I should still only poll when my five minutes is up and am
> online.  We don't want an extra sync in the middle.
>
>
>   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
>
> And push could lean on a NNP Notifier perhaps?
>
>
>> 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.
>
> Does ag-controller have an idea of privileged levels right now?
>

Yes, if combined with ag-sec :
https://github.com/aerogear/aerogear-controller-demo/blob/master/src/main/java/org/jboss/aerogear/controller/demo/Routes.java#L83

>
>
>
>>
>> 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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>
>
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