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Schema:
{ "fields" :
    [ {"name": "version", "type": "int", "doc": "version id"},
      {"name": "partitions",
        "type": {"type": "map",
                 "values": {"type": "array", "items": "int", "doc": "a list of replica ids"},
                 "doc": "a map from partition id to replica list"},
      }
    ]
}
Example:
{
  "version": 1,
  "partitions": {"0": [0, 1, 3] } }
}