[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 markberger):

 If I am remembering this correctly, !ServermapUpdater starts querying
 servers and it will stop after epsilon (k) servers have responded with no
 shares. However, the querying process can end while we know a server has
 shares, but we haven't finished communicating with it yet.

 So lets say our epsilon is 2, and we have three servers: A, B, and C.
 !ServermapUpdater will send queries to servers A, B, and C. Server A
 responds that it has shares, so !ServermapUpdater starts making more
 requests to get info about each share on server A. But before we can
 finish our transactions with server A, servers B and C respond that they
 have no shares. After servers B and C respond, !ServermapUpdater checks to
 see if it hit the epsilon limit. Since our limit is 2, the limit has been
 hit, and we start rejecting all responses from server A. Since we never
 finished our transaction with server A, a writer for server A was not
 created.

 This is an issue when the number of servers is greater than or equal to N
 + k because the querying process will not end until it receives feedback
 from N + k servers during a share write.

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Ticket URL: <https://tahoe-lafs.org/trac/tahoe-lafs/ticket/2034#comment:12>
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