Local/Remote Data

[Ruslan Zasukhin]

on 10/13/03 7:46, Deane Venske at dean at eduss.com wrote:

> Hi Ian,
> 
>> Yes. When the user chooses to "synchronize", the online data would be
>> updated to show any changes she has made and changes made by other
>> users would be downloaded to her machine.
> 
> First problem you're going to have is when changes have been made to the
> same data. Who's data is the most recent etc. We're busy writing
> software that has local and remote data sources. The fun part about ours
> is that we have 3 way communication :
>   School <-> Server <-> Home
> Everytime you come up with a solution, throw scenarios at it and see
> what you can think of. We've been working with this model for so long
> and still seem to get hiccups. It's one thing having a definite source
> of the most recent data and just getting information from it, but
> syncing is difficult.
> I would use timestamping over incrementing. This still doesn't save you
> when 1 person syncs before another and they've both changed the same
> data. In that case 1 of the people are going to lose their changes. Time
> stamping becomes slightly unreliable when you have people (I've had it
> happen to me) change their system clock.
> Ultimately your only safe bet is to have the data live. Always coming to
> and from the server. This can still result in someone's data being
> overwritten (John and mary edit the same customer at the same time) but
> you can put read/write locks in your code so that the server knows when
> someone has accessed a record and wont allow that record to be edited
> until the user has finished with it.
> 
> Bottom line is that data syncing can be a nightmare.

Correct,

As I have write to Ian in private mail,
The only standard way in big DBMS -- replication
Actually is ONE WAY synchronization way.

User A can change only tables A B C
User B can change only tables D E F
In this can we will not catch conflict.

2 WAY synchronization can be made only with REAL DATE TIME timestamp,
But again we loose data of one of user in case they modify the same record.
And this is not nice.

May be SECOND user, should get refuse and notification of conflict with ask
to resolve it, like this do CVS.

-- 
Best regards,
Ruslan Zasukhin      [ I feel the need...the need for speed ]
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e-mail: ruslan at paradigmasoft.com
web: http://www.paradigmasoft.com

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