[tahoe-lafs-trac-stream] [tahoe-lafs] #2034: Update for mutable files is sensitive to the number of servers

[tahoe-lafs]

#2034: Update for mutable files is sensitive to the number of servers
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     Reporter:  markberger    |      Owner:  markberger
         Type:  defect        |     Status:  new
     Priority:  normal        |  Milestone:  1.11.0
    Component:  code-mutable  |    Version:  1.10.0
   Resolution:                |   Keywords:  review-needed blocks-release
Launchpad Bug:                |
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Comment (by zooko):

 I just had a look at https://github.com/markberger/tahoe-
 lafs/commit/08f70b511345c9ae267ae90fe31adf5cee1fd723, but I wasn't sure I
 understood the issue. I thought maybe looking at a unit test would help me
 understand what this patch is fixing, but there is no unit test included
 in the patch. Then I came back and read this ticket's original message and
 started to understand it better.

 However, I still don't really understand it.

 > However, this can occur before the !ServermapUpdater? has added the
 server to the servermap, causing the client to reject the server's
 response. Since the server is not added to the servermap, a writer for
 that server is not created.

 When can this happen? Is this if there are > K servers in existence, and K
 servers have responded to queries, saying that they have no shares (or,
 perhaps some servers fail instead of responding "I have no shares"), and
 then… what happens? Is this server that "is not added to the servermap",
 mentioned above, one of the servers that has not yet been queried? Or it
 has been queried but it has not yet responded?

 Ideas:

 * Should we patch the unit tests, as described in the original message::

     "This race condition can be replicated by setting the number of
 servers for allmydata.test.test_mutable.Update to 13."

     ?
 * Should the resulting unit test have a comment giving this ticket # and
 URL to this ticket?

-- 
Ticket URL: <https://tahoe-lafs.org/trac/tahoe-lafs/ticket/2034#comment:9>
tahoe-lafs <https://tahoe-lafs.org>
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