Cluster Allocation Explain API

cluster allocation explanation API 的目的是帮助回答这个问题 “为什么这个分片没有被分配”。为了说明分片的分配（未分配状态），发出一个这样的请求 : 

$ curl -XGET 'http://localhost:9200/_cluster/allocation/explain' -d'{
  "index": "myindex",
  "shard": 0,
  "primary": false
}'

指定您希望查看的说明的 index 和 shard 的 id，和 primary 标记一样来指出是否 explain 一个主或者副本分片。

该响应如下 : 

{
  "shard" : {
    "index" : "myindex",
    "index_uuid" : "KnW0-zELRs6PK84l0r38ZA",
    "id" : 0,
    "primary" : false
  },
  "assigned" : false,                             ①
  "shard_state_fetch_pending": false,             ②
  "unassigned_info" : {
    "reason" : "INDEX_CREATED",                   ③
    "at" : "2016-03-22T20:04:23.620Z"
  },
  "allocation_delay_ms" : 0,                      ④
  "remaining_delay_ms" : 0,                       ⑤
  "nodes" : {
    "V-Spi0AyRZ6ZvKbaI3691w" : {
      "node_name" : "H5dfFeA",
      "node_attributes" : {                       ⑥
        "bar" : "baz"
      },
      "store" : {
        "shard_copy" : "NONE"                     ⑦
      },
      "final_decision" : "NO",                    ⑧
      "final_explanation" : "the shard cannot be assigned because one or more allocation decider returns a 'NO' decision",
      "weight" : 0.06666675,                      ⑨
      "decisions" : [ {                           ⑩
        "decider" : "filter",
        "decision" : "NO",
        "explanation" : "node does not match index include filters [foo:\"bar\"]"
      } ]
    },
    "Qc6VL8c5RWaw1qXZ0Rg57g" : {
      "node_name" : "bGG90GE",
      "node_attributes" : {
        "bar" : "baz",
        "foo" : "bar"
      },
      "store" : {
        "shard_copy" : "AVAILABLE"
      },
      "final_decision" : "NO",
      "final_explanation" : "the shard cannot be assigned because one or more allocation decider returns a 'NO' decision",
      "weight" : -1.3833332,
      "decisions" : [ {
        "decider" : "same_shard",
        "decision" : "NO",
        "explanation" : "the shard cannot be allocated on the same node id [Qc6VL8c5RWaw1qXZ0Rg57g] on which it already exists"
      } ]
    },
    "PzdyMZGXQdGhqTJHF_hGgA" : {
      "node_name" : "DKDM97B",
      "node_attributes" : { },
      "store" : {
        "shard_copy" : "NONE"
      },
      "final_decision" : "NO",
      "final_explanation" : "the shard cannot be assigned because one or more allocation decider returns a 'NO' decision",
      "weight" : 2.3166666,
      "decisions" : [ {
        "decider" : "filter",
        "decision" : "NO",
        "explanation" : "node does not match index include filters [foo:\"bar\"]"
      } ]
    }
  }
}

编号	描述
	Whether the shard is assigned or unassigned
	Whether information about the shard is still being fetched
	Reason for the shard originally becoming unassigned
	Configured delay before the shard can be allocated
	Remaining delay before the shard can be allocated
	User-added attributes the node has
	The shard copy information for this node and error (if applicable)
	Final decision and explanation of whether the shard can be allocated to this node
	Weight for how much the allocator would like to allocate the shard to this node
	List of node decisions factoring into final decision about the shard

对于一个已经分配的分片来说，输出与下面相似 : 

{
  "shard" : {
    "index" : "only-foo",
    "index_uuid" : "KnW0-zELRs6PK84l0r38ZA",
    "id" : 0,
    "primary" : true
  },
  "assigned" : true,
  "assigned_node_id" : "Qc6VL8c5RWaw1qXZ0Rg57g",      ①
  "shard_state_fetch_pending": false,
  "allocation_delay_ms" : 0,
  "remaining_delay_ms" : 0,
  "nodes" : {
    "V-Spi0AyRZ6ZvKbaI3691w" : {
      "node_name" : "bGG90GE",
      "node_attributes" : {
        "bar" : "baz"
      },
      "store" : {
        "shard_copy" : "NONE"
      },
      "final_decision" : "NO",
      "final_explanation" : "the shard cannot be assigned because one or more allocation decider returns a 'NO' decision",
      "weight" : 1.4499999,
      "decisions" : [ {
        "decider" : "filter",
        "decision" : "NO",
        "explanation" : "node does not match index include filters [foo:\"bar\"]"
      } ]
    },
    "Qc6VL8c5RWaw1qXZ0Rg57g" : {
      "node_name" : "I8hydUG",
      "node_attributes" : {
        "bar" : "baz",
        "foo" : "bar"
      },
      "store" : {
        "shard_copy" : "AVAILABLE"
      },
      "final_decision" : "ALREADY_ASSIGNED",        ②
      "final_explanation" : "the shard is already assigned to this node",
      "weight" : 0.0,
      "decisions" : [ {
        "decider" : "same_shard",
        "decision" : "NO",
        "explanation" : "the shard cannot be allocated on the same node id [Qc6VL8c5RWaw1qXZ0Rg57g] on which it already exists"
      } ]
    },
    "PzdyMZGXQdGhqTJHF_hGgA" : {
      "node_name" : "H5dfFeA",
      "node_attributes" : { },
      "store" : {
        "shard_copy" : "NONE"
      },
      "final_decision" : "NO",
      "final_explanation" : "the shard cannot be assigned because one or more allocation decider returns a 'NO' decision",
      "weight" : 3.6999998,
      "decisions" : [ {
        "decider" : "filter",
        "decision" : "NO",
        "explanation" : "node does not match index include filters [foo:\"bar\"]"
      } ]
    }
  }
}

编号	描述
	Node the shard is currently assigned to
	The decision is "ALREADY_ASSIGNED" because the shard is currently assigned to this node

您也可以让 Elasticsearch explain 第一个未分配分片的分配情况，它可以通过发送一个空的 body 来找到，例如 : 

$ curl -XGET 'http://localhost:9200/_cluster/allocation/explain'

如果您想要去包含所有的那些我们考虑到的最终的决策的决定，该 _include_yes_decisions _参数将返回所有的决策 : 

$ curl -XGET 'http://localhost:9200/_cluster/allocation/explain?include_yes_decisions=true'

此外，通过设置 include_disk_info_参数为 true_，您可以返回通过集群信息服务返回收集到的信息，包括硬盘使用和分配大小。

$ curl -XGET 'http://localhost:9200/_cluster/allocation/explain?include_disk_info=true'