Elasticsearch 7：分片 shard


#Elasticsearch 笔记

创建索引时指定多个分片

示例：

PUT student
{
  "mappings" : {
    "properties" : {
      "name" : {
        "type" : "keyword"
      }
    }
  },
  "settings" : {
    "index" : {
      "number_of_shards" : 8
    }
  }
}

哈希算法

按照官方的讨论 ，使用了 murmur3 哈希算法。 作为 ES 使用者，不需要关注具体的算法，因为不保证以后不会换成其他的算法。

routing 参数

在文档相关的增删改查API 中，均可指定 routing 参数进行分片路由。

查询结果中展示文档所属分片

创建索引：

PUT student
{
  "mappings" : {
    "properties" : {
      "name" : {
        "type" : "keyword"
      }
    }
  },
  "settings" : {
    "index" : {
      "number_of_shards" : 8
    }
  }
}

插入数据时指定 routing 用于路由分片：

POST student/_doc/1?routing=1
{
  "name": "name01"
}

POST student/_doc/2?routing=abc
{
  "name": "name02"
}

在查询中指定 explain 为 true，可以看到文档的 shard 信息：

GET student/_search
{
  "explain": true,
  "query": {
    "match_all": {}
  }
}

结果：

{
  "took" : 1,
  "timed_out" : false,
  "_shards" : {
    "total" : 8,
    "successful" : 8,
    "skipped" : 0,
    "failed" : 0
  },
  "hits" : {
    "total" : {
      "value" : 2,
      "relation" : "eq"
    },
    "max_score" : 1.0,
    "hits" : [
      {
        "_shard" : "[student][0]",
        "_node" : "wFhSfuLwR3OX21eldbRIHg",
        "_index" : "student",
        "_type" : "_doc",
        "_id" : "1",
        "_score" : 1.0,
        "_routing" : "1",
        "_source" : {
          "name" : "name01"
        },
        "_explanation" : {
          "value" : 1.0,
          "description" : "*:*",
          "details" : [ ]
        }
      },
      {
        "_shard" : "[student][5]",
        "_node" : "wFhSfuLwR3OX21eldbRIHg",
        "_index" : "student",
        "_type" : "_doc",
        "_id" : "2",
        "_score" : 1.0,
        "_routing" : "abc",
        "_source" : {
          "name" : "name02"
        },
        "_explanation" : {
          "value" : 1.0,
          "description" : "*:*",
          "details" : [ ]
        }
      }
    ]
  }
}

查询每个分片的信息

示例：

GET /student/_search_shards

如何指定查询某个分片中的数据

查询 shard 0 ：

GET student/_search?preference=_shards:0

结果：

{
  "took" : 0,
  "timed_out" : false,
  "_shards" : {
    "total" : 1,
    "successful" : 1,
    "skipped" : 0,
    "failed" : 0
  },
  "hits" : {
    "total" : {
      "value" : 1,
      "relation" : "eq"
    },
    "max_score" : 1.0,
    "hits" : [
      {
        "_index" : "student",
        "_type" : "_doc",
        "_id" : "1",
        "_score" : 1.0,
        "_routing" : "1",
        "_source" : {
          "name" : "name01"
        }
      }
    ]
  }
}

查询 shard 1：

GET student/_search?preference=_shards:1

结果：

{
  "took" : 0,
  "timed_out" : false,
  "_shards" : {
    "total" : 1,
    "successful" : 1,
    "skipped" : 0,
    "failed" : 0
  },
  "hits" : {
    "total" : {
      "value" : 0,
      "relation" : "eq"
    },
    "max_score" : null,
    "hits" : [ ]
  }
}


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