[jp] Goodbye, and thanks for all

Jack Haverty jack at 3kitty.org
Tue Jul 16 15:37:11 EDT 2013


I worked at Oracle for 8 years, and one thing I learned is that 
distributed databases are Real Hard Problems, especially when the 
players can be "offline".

Consider some kind of calendar server, "syncing" with a couple of PDAs 
occasionally.  Perhaps you and your spouse both have some kind of 
smartphone and you use them to coordinate your schedules.

You enter an appointment - say to go to a shopping mall, and allocate an 
hour to shop.

You later decide you need more time, so you can go to a another nearby 
store and pick up something.  So you use your PDA to change the 
appointment to add a half-hour.

Independently, your spouse remembers another errand in that vicinity, 
and also uses a PDA to change the appointment to allow more time for 
that, also adding a half-hour to the appointment.

Depending on when you and your spouse "sync" with the server, the server 
will also change the appointment to reflect the changes it has been told 
about.

The question is -- when the dust settles, how long is the appointment 
set to be?  Depends on who syncs when.  I haven't looked at iCal or 
DAVICal, but in systems I have looked at, admittedly years ago, a likely 
answer was that the server would have concluded the appointment should 
be 1-1/2 hours long.  But you actually need two hours to do all your 
errands.   You can imagine lots of other similar scenarios where the end 
result is the wrong answer in the server database.  Any time when you 
have more than one device syncing to the same server you're potentially 
in trouble.  Distributed databases are Real Hard Problems...

What happens in this experiment when using iCal, DAVICal, etc...? It 
would be great to hear that they've solved this kind of problem.

The "folder/file sync" is not a solution to this problem either. You 
still have to be careful in how you use it.  But I've found that it's 
sufficient, if a little unwieldy, as an interim solution until someone 
creates the apps/servers that do it "right".   My ancient Palm just 
wasn't going to last much longer.  so, for now, the file/folder scheme 
lets me use my Android phone and tablet, as long as I'm careful about 
the syncing behavior.

/Jack


On 07/16/2013 11:08 AM, Johan Vromans wrote:
> "James E. LaBarre" <j.e.labarre at gmail.com> writes:
>
>> The problem with anything like Foldersync is it's a file-level sync;
>> PalmOS/jpilot operates on a record-level sync. Not much good if you
>> want to use a system offline, then replicate the changes later.
> That's why for agenda and contacts it is much better to use an iCal
> server like DAViCal. These work on a per-appointment (contact) basis.
>
> -- Johan
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