Elasticsearch load is low, batch write latency is high, how to check the problem

elasticsearch load is low, batch write latency is high, how to check the problem , thanks

13:24:27 22.6s{
  "completed" : false,
  "task" : {
    "node" : "6nPgzz7_Q96pQzAompMFUQ",
    "id" : 470791605,
    "type" : "transport",
    "action" : "indices:data/write/bulk[s]",
    "status" : {
      "phase" : "rerouted"
    },
    "description" : "requests[1178], index[order_474]",
    "start_time_in_millis" : 1617197067488,
    "running_time_in_nanos" : 23322629616,
    "cancellable" : false,
    "parent_task_id" : "6nPgzz7_Q96pQzAompMFUQ:470791598",
    "headers" : { }
  }
}
13:24:27 22.5s{
  "completed" : false,
  "task" : {
    "node" : "U8NwB6i1SAWLpu8tX4241A",
    "id" : 133112682,
    "type" : "netty",
    "action" : "indices:data/write/bulk[s]",
    "status" : {
      "phase" : "waiting_on_primary"
    },
    "description" : "requests[1178], index[order_474]",
    "start_time_in_millis" : 1617197067527,
[root@CCLT-BL000591 .y]# head -n 50 c.txt 
13:24:23 26.8s{
  "completed" : false,
  "task" : {
    "node" : "U8NwB6i1SAWLpu8tX4241A",
    "id" : 133111967,
    "type" : "netty",
    "action" : "indices:data/write/bulk[s]",
    "status" : {
      "phase" : "waiting_on_primary"
    },
    "description" : "requests[612], index[item_411]",
    "start_time_in_millis" : 1617197063224,
    "running_time_in_nanos" : 26965101894,
    "cancellable" : false,
    "parent_task_id" : "r6gbkwdTRDSUUooaLfWZPw:861626961",
    "headers" : { }
  }
}
13:24:23 26.8s{
  "completed" : false,
  "task" : {
    "node" : "U8NwB6i1SAWLpu8tX4241A",
    "id" : 133111968,
    "type" : "direct",
    "action" : "indices:data/write/bulk[s][p]",
    "status" : {
      "phase" : "primary"
    },
    "description" : "requests[612], index[item_411]",
    "start_time_in_millis" : 1617197063226,
    "running_time_in_nanos" : 26972116722,
    "cancellable" : false,
    "parent_task_id" : "U8NwB6i1SAWLpu8tX4241A:133111967",
    "headers" : { }
  }
}
13:24:23 26.5s{
  "completed" : false,
  "task" : {
    "node" : "np9WVtzUQNOMFWrfksfq7g",
    "id" : 1100912635,
    "type" : "transport",
    "action" : "indices:data/write/bulk[s]",
    "status" : {
      "phase" : "rerouted"
    },
    "description" : "requests[396], index[item_411]",
    "start_time_in_millis" : 1617197063561,
    "running_time_in_nanos" : 26641739744,
    "cancellable" : false,

I believe you will need to provide a bit more information in order for someone to be able to help.

Which version of Elasticsearch are you using?

What is your use case?

What is the specification of your Elasticsearch cluster in terms of number of nodes, hardware, type of storage used and configuration?

What is the full output of the cluster stats API?