求教熔断器parent的值是怎么算的

根据接口_nodes/stats/breaker?pretty，得到

{

  "_nodes" : {

    "total" : 1,

    "successful" : 1,

    "failed" : 0

  },

  "cluster_name" : "es",

  "nodes" : {

    "Ru5FtxEfSHma23mXhzy3ig" : {

      "timestamp" : 1600248223372,

      "roles" : [

        "master",

        "ingest",

        "data",

        "ml"

      ],

      "attributes" : {

        "ml.machine_memory" : "33565143040",

        "ml.max_open_jobs" : "20",

        "xpack.installed" : "true",

        "box_type" : "hot",

      },

      "breakers" : {

        "request" : {

          "limit_size_in_bytes" : 6871947673,

          "limit_size" : "6.3gb",

          "estimated_size_in_bytes" : 0,

          "estimated_size" : "0b",

          "overhead" : 1.0,

          "tripped" : 0

        },

        "fielddata" : {

          "limit_size_in_bytes" : 3435973836,

          "limit_size" : "3.1gb",

          "estimated_size_in_bytes" : 413791928,

          "estimated_size" : "394.6mb",

          "overhead" : 1.03,

          "tripped" : 0

        },

        "in_flight_requests" : {

          "limit_size_in_bytes" : 17179869184,

          "limit_size" : "16gb",

          "estimated_size_in_bytes" : 374,

          "estimated_size" : "374b",

          "overhead" : 2.0,

          "tripped" : 0

        },

        "accounting" : {

          "limit_size_in_bytes" : 17179869184,

          "limit_size" : "16gb",

          "estimated_size_in_bytes" : 3523929685,

          "estimated_size" : "3.2gb",

          "overhead" : 1.0,

          "tripped" : 0

        },

        "parent" : {

          "limit_size_in_bytes" : 15461882265,

          "limit_size" : "14.3gb",

          "estimated_size_in_bytes" : 13101554952,

          "estimated_size" : "12.2gb",

          "overhead" : 1.0,

          "tripped" : 3233

        }

      }

    }

  }

}

parent的estimated_size为啥不等于accounting+in_flight_requests+fielddata+request的estimated_size之和