Re: [Storagesync] Storagesync Digest, Vol 5, Issue 1

[Linhui Sun <[e-mail]>]

On 周一, 12月 7, 2015 at 08:38, Markus Unterwaditzer <[e-mail]>
wrote:
On Mon, Dec 07, 2015 at 08:31:55AM +0800, Linhui Sun wrote:
> The server only need to know the latest version in my view. They don't need to
> be able to identify last sync or change, just to check whether metadata file
is
> latest is enough.

The metadata file contains all etags *for all files* from the previous sync. It
is stored on the clientside and is never sent to the server. So the local metadata file is for client to decide whether to send a content.
But what if the file has been changed during two sync processes by another
participant who also shares the file.

>
> On Mon, Dec 07, 2015 at 08:17:26AM +0800, Linhui Sun wrote:
> > On 周一, 12月 7, 2015 at 01:36, Markus Unterwaditzer <[e-mail]>
> > wrote:
> > > IMO, etag is designed for client side cache. A typical usage: if the file
> > > on the server has no actual change, the client will use the cache and the
> > > server does not need to send the file content again. While for a storage
> > > service, we also need some some similar mechanism at server side. In this
> > > way, the client do not need to upload unchanged content to the server.
> >
> > There is no "true-and-only" usecase for etags, and no, you do not need
> anything
> > more than etags for synchronization. Using a additional "metadata" file, the
> > client can cheaply determine whether local content changed and whether
server
> > content changed, and that's all that is required for (in this case) file
> > synchronization. Sync conflicts are a different story, and the solution to
> that
> > heavily depends on the kind of data you're syncing. I'm a little bit
confused
> here: if I have a metadata file, why do I still need
> > the etag? The metadata file should contain something equivalent to the etag.
> >
> > >
> > > > --
> > > > Sent from my phone. Please excuse my brevity.
> > > >
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