[gpodder-devel] my.gpodder episode sync design problem: "since" values
- From: dovdevel at gmail.com (Dov Feldstern)
- Date: Fri, 1 Jul 2011 17:54:46 +0300
On Fri, Jul 1, 2011 at 16:54, Dov Feldstern <dovdevel at gmail.com> wrote:
> On Fri, Jul 1, 2011 at 16:29, Neal H. Walfield <neal at walfield.org> wrote:
>> At Fri, 1 Jul 2011 15:35:52 +0300,
>> Dov Feldstern wrote:
>>> 3. n900 at 9:18 : connects to network, stored actions are uploaded; so
>>> the action from step (1) is now uploaded, *but its timestamp is still
>>> "9:14"*! Since "9:14" is earlier than the new "since" value ("9:16"),
>>> the episode action will never get synced back to the desktop...
>>
>>> So, I think that the "timestamp" stored with actions is *not* the
>>> value which should be used for purposes of comparing with "since"
>>> values and syncing; rather, an "upload-timestamp" should be stored
>>> server-side, which would serve for this purpose.
>>
>> Why not use Lamport timestamps to do the ordering?
>>
>> ?http://en.wikipedia.org/wiki/Lamport_timestamps
>>
>> Neal
>
> Hmmm, first of all, because I was not familiar with Lamport timestamps ;) .
>
> However, after skimming over the article, I think they solve a
> different problem than the one we're facing. In our case, there's a
> single point of reference (the server), so we really don't have a
> problem of ordering events -- we can *know* the *exact* order in which
> the events happen on the server, which is what's important for
> syncing.
>
> Our problem is that there are really two different events happening
> (the actions themselves, and the actions upload) at two different
> times (action-time, upload-time). For sync purposes, only the
> upload-time is interesting; however, we're confusing the two times,
> and using action-times for dync purposes, which is what's causing the
> problem.
>
> So, I don't really think that Lamport timestamps can help us out here,
> though they may be useful if some kind of client-to-client
> synchronization, which does not go through a central server, is ever
> implemented...
>
> Thanks!
> Dov
>
Thinking about this a bit more, I think that using server-based
action-upload times would also solve / obviate the need for solving
https://bugs.gpodder.org/show_bug.cgi?id=1366 .
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