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

[Markus Unterwaditzer <[e-mail]>]

Note that this is not specific to remoteStorage. This is how WebDAV sync
clients work in practice (not via the sync protocol, which is not popular
enough), it is how remoteStorage sync clients work in practice. At least in
terms of the kind of data they access from server and client, the exact
algorithm may be different.

On Mon, Dec 07, 2015 at 01:33:20PM +0100, Markus Unterwaditzer wrote:
> > > That works, but do you think this could make the things complicated? It
> > > sounds like different situations have different mechanisms. Why not just
> > > make the metadata exchanged, any disadvantage for doing that?
> > 
> > > I don't know what that means.
> 
> > The question is why you just keep the metadata locally at client side but not
> > exchange the metadata between client and server to make both of them (both
> > peers) have the latest metadata store in time.
> 
> I think we have a misunderstanding here.
> 
> We have a server storage that has an etag for each file. We have a client
> storage that has an etag for each file.
> 
> The sync client accesses those *and* a "status" file that contains a list of
> all files + etags for *both* sides, as they were after the previous sync.  This
> is similar to the algorithm described in
> http://blog.ezyang.com/2012/08/how-offlineimap-works/, except that one doesn't
> deal with files being modified. As said, this warrants a longer blogpost, but I
> don't have the time to write one now.
> 
> > 
> > >
> > > >
> > > > >
> > > > > >
> > > > > > 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.
> > > > > > > > >
> > > > > > > > > _______________________________________________
> > > > > > > > > Storagesync mailing list
> > > > > > > > > [e-mail]
> > > > > > > > > [https://www.ietf.org/mailman/listinfo/storagesync] https://www.ietf.org/mailman/listinfo/storagesync
> > [https://www.ietf.org/mailman/listinfo/storagesync]
> > > > > > > > >
> > > > > > >
> > > > > > > > _______________________________________________
> > > > > > > > Storagesync mailing list
> > > > > > > > [e-mail]
> > > > > > > > [https://www.ietf.org/mailman/listinfo/storagesync] https://www.ietf.org/mailman/listinfo/storagesync
> > [https://www.ietf.org/mailman/listinfo/storagesync]
> > > > > >
> > > > > > > _______________________________________________
> > > > > > > Storagesync mailing list
> > > > > > > [e-mail]
> > > > > > > [https://www.ietf.org/mailman/listinfo/storagesync] https://www.ietf.org/mailman/listinfo/storagesync
> > [https://www.ietf.org/mailman/listinfo/storagesync]
> > > >
> > 
> > > _______________________________________________
> > > Storagesync mailing list
> > > [e-mail]
> > > [https://www.ietf.org/mailman/listinfo/storagesync] https://www.ietf.org/mailman/listinfo/storagesync
> > [https://www.ietf.org/mailman/listinfo/storagesync]