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  1. Core Server
  2. SERVER-28333

Question about network partition and replica set

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    • Icon: Question Question
    • Resolution: Done
    • Icon: Major - P3 Major - P3
    • None
    • 3.2.11
    • Replication
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    Description

      Hello there,
      I have a question about a possible scenario happened with a replica set, involving a network partition. Mongo version is 3.2.11

      Let's suppose to have 3 nodes: A, B, C. A is the primary. B, C are secondary.
      Suddendly a network partition happens and it continues for lot of hours. During the network partition A and B can connect, as well as B and C.
      If I correctly understand how replication works:

      • A still see a majority of nodes and remains primary
      • C don't see A and thus attempts to start an election
      • C is disconnected from A and thus its data become older and older
      • B still see A and thus ignores the request for election from B
      • B continues to replicate from A

      Now let's suppose that, after a lot of hours, without fixing the network partition, node A crashes.
      If I'm correct B and C will start and election.

      The question is: are we 100% sure that the election will result in the node B (which is synchronized with A) to be elected as primary ?
      Or there is a possibility that instead the node C (which has very old data).

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            kelsey.schubert@mongodb.com Kelsey Schubert
            aldo Aldo
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