Re: Offline scenario with low bandwith
From: Steve B. (steve_beauge_at_com.msn.Swap.dotcom.and.msn)
Date: 01/28/05
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Date: Fri, 28 Jan 2005 09:17:33 +0100
Here are results of my investigation, FYI:
SQL replication transmits only changes.
SQL replication allows filtering data horizontally, using some builtin
functions, like SUSER_SNAME to work with a subset of data.
So the first time the application is launched, user-specific data and common
data are downloaded. Next times, the replication mechanisms detect changes
in subscribers and publisher to exchange only the required data.
That answers all of my questions.
Steve
"Darren Shaffer" <darrenshaffer@discussions.microsoft.com> a écrit dans le
message de news: %237nsNpzAFHA.612@TK2MSFTNGP09.phx.gbl...
> Steve,
>
> The idea of replicating a 40-60MB database across GPRS is not going to
> perform well, regardless of your choice of RDA, Merge, or a custom
> web-services-based
> replication strategy. GPRS today has about a 40kbps bandwidth and this is
> simply
> too much data for that bandwidth. Here are some suggestions for you:
>
> 1. figure out how to deploy the initial (very large) SQL CE database to
> your mobile
> users pre-loaded with reference/static data. In most systems, this type
> of data is the bulk
> of what needs to be on device anyway. You can create your .SDF file once
> loaded in this manner, include it as Content in your Visual Studio
> project, and deploy it
> along with your application to your users via CAB files or on memory
> cards.
>
> 2. create a web service on IIS that exposes methods to update the central
> server
> with datasets or diffgrams sent from the mobile users. only send what you
> must over
> GPRS to the central server. you'll have to manage conflicts yourself, but
> two tips to
> minimize these conflicts - 1) use GUIDs for everything unique across
> mobile users and
> 2) try to architect in such a way that you can do "deletes" and "inserts"
> rather than "updates"
> on the central server. don't be intimidated by building your own web
> services replication
> strategy - it's not as big as it sounds and gives you very fine-grained
> control over every aspect of
> the data replication.
>
> 3. delete data that has been successfully sent to the central server from
> the local devices
> (if it is no longer needed on device). be sure to compact your SQL CE
> database at frequent intervals
> to reclaim unused space and re-calculate index statistics (improving
> performance).
>
> When Microsoft built a mobile client for their CRM product, they used a
> hybrid approach
> involving RDA and web services to address this issue. A case study
> explaining that architecture
> is available at: http://www.only4gurus.com/v3/download.asp?ID=5511 and
> more detailed
> coverage in an Oct 2004 .Net Developer's Journal article that covers it
> (you must be
> a subscribed to obtain it).
>
> Darren Shaffer
> Principal Architect
> Connected Innovation
>
>
> "Steve B." <steve_beauge@com.msn.Swap.dotcom.and.msn> wrote in message
> news:41f6585c$0$20324$626a14ce@news.free.fr...
>> Hello,
>>
>> I'm working on an application that will be based on Pocket PC devices for
>> clients, and an office server.
>>
>> The central server will hold all data, and mobile users need to hold
>> their own data and product catalog (up to 60 MB).
>> When a user type something, it should be stored locally, and
>> periodically, the updates need to be applied to the main system, while
>> new products and chaged products are grabbed.
>>
>> I'm prototyping SQL CE to reach my goal, but I have some difficulties to
>> understant the architecture. Here it is what I suppose :
>>
>> The main server runs IIS 6.0, SQL Server 2000 and SQL CE agent
>> (configured and working).
>> The mobile device run SQL Server CE.
>>
>> The application (written in C#) works directly in the local SQL Ce DB.
>> When the network is available (typically when the user connect its device
>> to a GPRS network), the Remote Data Access object uploads changed data
>> (push), then drop table and download the entire table (pull).
>>
>> This process is not acceptable because of the heavy data that require to
>> transit on network (actually the 40 MB).
>>
>> So I wonder if I missed something.
>>
>> 1. Is it possible to pull only required data instead of pulling the whole
>> table (i.e. changed tables, deleted tables and insterted tables since the
>> last sync)?
>> 2. Where are located conflicted rows ?
>> 3. How whould you do to reach my goal ?
>>
>> Hope that you'll help in getting answers.
>>
>> Thanks,
>> Steve
>>
>
>
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