ES内存使用过高

ES的集群的配置：
三台服务器，每台服务器的内存是18G，硬盘800G，
分配ES内存是8G
数据量在白天半小时的数据量是480万，算下来每秒钟会有2660的数据量。ES 集群在运行的时候内存的使用率居高不下，下面是集群的信息：

{

  "_nodes" : {

    "total" : 3,

    "successful" : 3,

    "failed" : 0

  },

  "cluster_name" : "ES",

  "timestamp" : 1509951969945,

  "status" : "green",

  "indices" : {

    "count" : 99,

    "shards" : {

      "total" : 982,

      "primaries" : 491,

      "replication" : 1.0,

      "index" : {

        "shards" : {

          "min" : 2,

          "max" : 10,

          "avg" : 9.919191919191919

        },

        "primaries" : {

          "min" : 1,

          "max" : 5,

          "avg" : 4.959595959595959

        },

        "replication" : {

          "min" : 1.0,

          "max" : 1.0,

          "avg" : 1.0

        }

      }

    },

    "docs" : {

      "count" : 1013971510,

      "deleted" : 66960

    },

    "store" : {

      "size" : "1.2tb",

      "size_in_bytes" : 1373088950761,

      "throttle_time" : "0s",

      "throttle_time_in_millis" : 0

    },

    "fielddata" : {

      "memory_size" : "452.6mb",

      "memory_size_in_bytes" : 474654080,

      "evictions" : 0

    },

    "query_cache" : {

      "memory_size" : "619.7mb",

      "memory_size_in_bytes" : 649838032,

      "total_count" : 3010207,

      "hit_count" : 395960,

      "miss_count" : 2614247,

      "cache_size" : 45228,

      "cache_count" : 62364,

      "evictions" : 17136

    },

    "completion" : {

      "size" : "0b",

      "size_in_bytes" : 0

    },

    "segments" : {

      "count" : 12777,

      "memory" : "3.3gb",

      "memory_in_bytes" : 3619016398,

      "terms_memory" : "2.9gb",

      "terms_memory_in_bytes" : 3143711676,

      "stored_fields_memory" : "346.6mb",

      "stored_fields_memory_in_bytes" : 363456936,

      "term_vectors_memory" : "0b",

      "term_vectors_memory_in_bytes" : 0,

      "norms_memory" : "19.8mb",

      "norms_memory_in_bytes" : 20776576,

      "points_memory" : "31.6mb",

      "points_memory_in_bytes" : 33171794,

      "doc_values_memory" : "55.2mb",

      "doc_values_memory_in_bytes" : 57899416,

      "index_writer_memory" : "86.9mb",

      "index_writer_memory_in_bytes" : 91152660,

      "version_map_memory" : "703kb",

      "version_map_memory_in_bytes" : 719948,

      "fixed_bit_set" : "0b",

      "fixed_bit_set_memory_in_bytes" : 0,

      "max_unsafe_auto_id_timestamp" : 1509928479068,

      "file_sizes" : { }

    }

  },

  "nodes" : {

    "count" : {

      "total" : 3,

      "data" : 3,

      "coordinating_only" : 0,

      "master" : 3,

      "ingest" : 3

    },

    "versions" : [

      "5.2.2"

    ],

    "os" : {

      "available_processors" : 18,

      "allocated_processors" : 18,

      "names" : [

        {

          "name" : "Linux",

          "count" : 3

        }

      ],

      "mem" : {

        "total" : "52.4gb",

        "total_in_bytes" : 56268460032,

        "free" : "878.2mb",

        "free_in_bytes" : 920948736,

        "used" : "51.5gb",

        "used_in_bytes" : 55347511296,

        "free_percent" : 2,

        "used_percent" : 98

      }

    },

    "process" : {

      "cpu" : {

        "percent" : 43

      },

      "open_file_descriptors" : {

        "min" : 963,

        "max" : 1071,

        "avg" : 1031

      }

    },

    "jvm" : {

      "max_uptime" : "4.7d",

      "max_uptime_in_millis" : 406672392,

      "versions" : [

        {

          "version" : "1.8.0_131",

          "vm_name" : "Java HotSpot(TM) 64-Bit Server VM",

          "vm_version" : "25.131-b11",

          "vm_vendor" : "Oracle Corporation",

          "count" : 3

        }

      ],

      "mem" : {

        "heap_used" : "12.3gb",

        "heap_used_in_bytes" : 13294911944,

        "heap_max" : "23.8gb",

        "heap_max_in_bytes" : 25612910592

      },

      "threads" : 283

    },

    "fs" : {

      "total" : "2.3tb",

      "total_in_bytes" : 2576948920320,

      "free" : "1tb",

      "free_in_bytes" : 1178129113088,

      "available" : "1tb",

      "available_in_bytes" : 1178129113088,

      "spins" : "true"

    },

    "plugins" : [ ],

    "network_types" : {

      "transport_types" : {

        "netty4" : 3

      },

      "http_types" : {

        "netty4" : 3

      }

    }

  }

}

我现在有两个问题：
1、是不是这个配置低了？有那方面可以调优？
2、下面这段，摘自上面的jvm里面，堆内存其实只是用了一般左右，但是总的内存是使用到了98%，ES默认的堆内存是锁死吗？
"mem" : { "heap_used" : "12.3gb", "heap_used_in_bytes" : 13294911944, "heap_max" : "23.8gb", "heap_max_in_bytes" : 25612910592 },