Interrupted sync causes duplicate uploads to WebDAV

First of all, I have to say that the sync feature is really awesome (as is Zotero in general). Great work! :-)

However, here's a somewhat frustrating problem I've encountered a couple of times now. (Sorry if it's already been raised elsewhere... I couldn't find it). I'm using Zotero 1.5b2 in FF3, running Windows XP:

This occurs when I've had a sync interrupted by some external problem (e.g. broken Internet connection, or browser crash). If that happens in the middle of Zotero downloading lots of data files from my WebDAV server, then it doesn't seem to realise that the files came from a sync. Instead, it knows the files are there, but treats them as being new additions to my library. As such, when I attempt to resume the sync, it starts trying to upload the files to WebDAV. The sometimes creates inevitable conflicts, and at least causes a bunch of unnecessary uploads/downloads.

The only good solution I've found to this problem is simply to delete my local copy of the Zotero data, and either re-download everything from sync, or restore locally from a backup or other 'clean' copy (e.g. from another machine). That's really not ideal though, as I use Zotero to store rather a lot of data files, so it's a lot of stuff to transfer.

Hopefully the syncs can be made more atomic in the final version of 1.5, so that a partial sync doesn't break stuff? In the meantime though, is there anything I can do when this does occur... e.g. instruct Zotero to roll-back the broken sync or something?
  • Metadata syncing is already atomic, but file syncing shouldn't need to be atomic—it should be able to be interrupted at any time without trouble. We'll see if we can reproduce the problem you're seeing.
  • Hi Dan. Any success reproducing the problem?

    In the meantime, I've been trying to sync my home PC again using the 1.5b2.1 release. I completely deleted my local Zotero folder, and told it to restore everything from the server. The metadata was fine, and the storage download seemed to proceed as normal (getting 323 files). After quite a while though, it was still syncing. Hovering the mouse over the sync progress bar indicated that the downloads had finished, but it was proceeding to *upload* 323 files. (Oddly, no file conflicts were reported though.)

    I am just letting it run through the upload for now, and when I get into work tomorrow, I'll see what happens when I sync from there. (That's the PC I usually use Zotero from.)

    Incidentally, the same thing tries to happen on my laptop too, so I've reproduced it without doing anything special, as far as I know. Perhaps there could be something specific in my collection which is causing a problem? Would debug output be likely to capture anything useful?
  • I can confirm the problem peterbloomfield is describing.

    In my hands it occurred on 2 different PCs that sync to the same account. Deleting the zotero folder does not help. Restoring from the server doesn't help either. I couldn't find what triggered the problem. There are no errors associated with it. With me it does not affect the entire collection.
  • I just tried to clear the problem by uninstalling zotero, deleting the entire mozilla and zotero folders (I had the zotero folder on a separate disk partition). After that I installed zotero and synced from the server. It downloaded 768 files and immediately after that it started uploading 195 files (the same number of files it was trying to upload previously). This makes me thing the problem is not with the local client but with the server (either zotero or the webdav storage). I don't know enough how the syncing logic works to figure out what exactly went wrong.
  • Thanks for confirming the problem pesho.

    I just synced from my work PC (Zotero 1.5b2.1, in FF3 running on Vista Home Premium). As before, the metadata was fine, and it started downloading *all* files for storage sync (337 now), even though almost all of them were already on my local collection here. Once again, it then proceeded to upload them all yet again to my WebDAV server. No errors or file conflicts were reported.

    Perhaps there is a problem syncing between different operating systems?

    One other random possibility (a total shot in the dark) is that I have several documents on my work PC which are not stored in Zotero, but there are links from Zotero items to those documents. Those documents are not on my other computers, and obviously they are not carried across in the sync, but presumably the names/paths of the files are carried over in metadata. Could the storage sync be getting confused by the absence of those files?
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