While API 0.6 have implemented object versioning, preventing accidentally overwriting someone else's changes, with introduction of atomic uploads now I see many problems with duplicate data.
These come often with imports of data or generally if someone uploads any new data without modifying any existing data (like if someone just traces hundreds of buildings from ortophoto, or alike ....) Since in JOSM (and possibly in other tools) the atomic upload is the default method, that user presses some "upload" button and in few seconds all the changes are uploaded to the server, which then starts processing it (this could take some time for larger changes) and once it is finished, it will send new node ID's back to the editor. Unfortunately, sometimes while waiting for server to process the uploaded data, the connection will timeout, so the user sees some error message - thinking the upload failed, he presses "upload" again, starting to push new copy of all the objects to the server. Later, the server want to return ID's from first upload, but nobody is listening on the orher end anymore. Ultimate result is sometimes having 2 to 4 identical copies of some data, sometimes it is thousands of duplicate nodes and ways. Suggestion for one possible countermeasure: after server receives complete succesful atomic upload from user, compute SHA1, MD5, or some other checksum of the uploaded XML. Store it and if user tries uploading exactly the same thing again (because he thinks the upload have failed, which is not true), send him just some error message instead, like: "You have already uploaded this data". Or alternatively, send the user whatever result was there from the last upload (either new set of ID's, or some error message in case that previous upload failed because of some error) I think perhaps last 2 or 3 checksums could be stored in case someone have multiple parallel uploads in multiple editors. Martin _______________________________________________ talk mailing list [email protected] http://lists.openstreetmap.org/listinfo/talk
