[tahoe-lafs-trac-stream] [Tahoe-LAFS] #2814: "simultaneuous" edits not caught

[Tahoe-LAFS]

#2814: "simultaneuous" edits not caught
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     Reporter:  meejah                      |      Owner:  daira
         Type:  defect                      |     Status:  new
     Priority:  normal                      |  Milestone:  undecided
    Component:  code-frontend-magic-folder  |    Version:  1.11.0
   Resolution:                              |   Keywords:
Launchpad Bug:                              |
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Comment (by meejah):

 Really, I think this is actually another example of needing a better
 strategy than simple versioning. Also, it's really that we're not even
 downloading the other person's file (and therefore also not detecting a
 conflict).

 When Alice and Bob see the new file, they both believe that it's new; so
 they both upload a "version=0" file. (So in their own private collective-
 dirs, they each create a new file). When they try to sync next, they both
 see that they other side has a "version=0" file (which is the same as the
 biggest version in their local database, so nothing to do).

 What the "other" side really needs to determine what to do is something
 like a vector-clock, so they can tell "bob thought his file was new when
 he uploaded it" and then alice can conclude that it was a conflict
 (because she also though it was new).

 In this particular case, it might be sufficient to record *whose* version
 is in the local database (rather than just the plain version). Then, bob
 or alice can correctly conclude that they need to download. (I.e. bob will
 see "bob's version 0" is what he has, but alice also has a version 0 so he
 can conclude that she uploaded her own version 0 before seeing his, or her
 version would be 1).

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Ticket URL: <https://tahoe-lafs.org/trac/tahoe-lafs/ticket/2814#comment:1>
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