Re: [Gnumed-devel] Synching

[Thiemo Kellner]

> > Hm, actually a transaction is exactly what does this.
>
> Well, but not disconnected.

:-) As I pointed out too.

> > What I was thinking about that the GnuMed client might be able to
> > cache data and make changes on that information.
>
> That'd effectively mean implementing master-master
> replication with conflict resolution right in the client
> which is something far bigger players have failed at.
>
> > And only when
> > connection to the database is available again, the changes would get
> > transferred to the database.
>
> The hard problem isn't so much caching of data in
> disconnected mode but rather resolution of conflicts later on.

I fully agree that it would be a hard thing to implement a fully  
automatic conflict resolution. I'd even say it is impossible if you  
are to catch all cases. But I also think that it is completely  
unnecessary. The confict can be solved by who ever is trying to synch.  
It just would be handy for the one to have a tool supporting this.

On the other hand, if one took the approach to only add data, would it  
not be possible to have an automatic synch assuming that the order of  
the entries where of no importance. I guess one could even get an  
appropriate time order when the client would save the local  
uncommitted entry with its save timestamp and this timestamp would get  
committed to the database as well. Even if we ommitted the ordering,  
conficts would only raise if more than one visit would take place in  
at the "same" time or when the earlier visitor was lazy and would not  
synch as soon as possible. I reckon this is not often the case.

Thinking of all this. Couldn't conficts occur in GnuMed already. At  
the end it is client server technology and two (or more) clients  
accessing the same data would cache this data and if both of those  
clients changed the data, one would necessarily try to commit with  
outdated base data.

Never mind. If master client replication works it will fit my purpose anyway.

Cheers

Thiemo

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