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  1. Infinispan
  2. ISPN-4949

Split brain: inconsistent data after merge

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      1) cluster A, B, C, D splits into 2 parts:
      A, B (coord A) finds this out immediately and enters degraded mode with CH [A, B, C, D]
      C, D (coord D) first detects that B is lost, gets view A, C, D and starts rebalance with CH [A, C, D]. Segment X is primary owned by C (it had backup on B but this got lost)
      2) D detects that A was lost as well, therefore enters degraded mode with CH [A, C, D]
      3) C inserts entry into X: all owners (only C) is present, therefore the modification is allowed
      4) cluster is merged and coordinator finds out that the max stable topology has CH [A, B, C, D] (it is the older of the two partitions' topologies, got from A, B) - logs 'No active or unavailable partitions, so all the partitions must be in degraded mode' (yes, all partitions are in degraded mode, but write has happened in the meantime)
      5) The old CH is broadcast in newest topology, no rebalance happens
      6) Inconsistency: read in X may miss the update

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              dberinde@redhat.com Dan Berindei
              rvansa1@redhat.com Radim Vansa (Inactive)
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