elasticsearch学习笔记(三十四)——Elasticsearch 基于scoll技术滚动搜索大量数据

newbornzhao 2019-07-01

在实际应用中,通过from+size不可避免会出现深分页的瓶颈,那么通过scoll技术就是一个很好的解决深分页的方法。比如如果我们一次性要查出10万条数据,那么使用from+size很显然性能会非常的差,priority queue会非常的大。此时如果采用scroll滚动查询,就可以一批一批的查,直到所有数据都查询完。

scroll原理

scoll搜索会在第一次搜索的时候,保存一个当时的视图快照,之后只会基于该旧的视图快照提供数据搜索,如果这个期间数据变更,是不会让用户看到的。而且ES内部是基于_doc进行排序的方式,性能较高。
示例:

POST /test_index/_search?scroll=1m
{
  "query": {
    "match_all": {}
  },
  "sort": [
    "_doc"
  ],
  "size": 3
}

{
  "_scroll_id" : "DXF1ZXJ5QW5kRmV0Y2gBAAAAAAABu4oWUC1iLVRFdnlRT3lsTXlFY01FaEFwUQ==",
  "took" : 7,
  "timed_out" : false,
  "_shards" : {
    "total" : 1,
    "successful" : 1,
    "skipped" : 0,
    "failed" : 0
  },
  "hits" : {
    "total" : {
      "value" : 10,
      "relation" : "eq"
    },
    "max_score" : null,
    "hits" : [
      {
        "_index" : "test_index",
        "_type" : "_doc",
        "_id" : "1",
        "_score" : null,
        "_source" : {
          "field1" : "one"
        },
        "sort" : [
          0
        ]
      },
      {
        "_index" : "test_index",
        "_type" : "_doc",
        "_id" : "2",
        "_score" : null,
        "_source" : {
          "field1" : "two"
        },
        "sort" : [
          1
        ]
      },
      {
        "_index" : "test_index",
        "_type" : "_doc",
        "_id" : "3",
        "_score" : null,
        "_source" : {
          "field1" : "three"
        },
        "sort" : [
          2
        ]
      }
    ]
  }
}
POST /_search/scroll
{
  "scroll": "1m",
  "scroll_id": "DXF1ZXJ5QW5kRmV0Y2gBAAAAAAABu4oWUC1iLVRFdnlRT3lsTXlFY01FaEFwUQ=="
}
{
  "_scroll_id" : "DXF1ZXJ5QW5kRmV0Y2gBAAAAAAABu4oWUC1iLVRFdnlRT3lsTXlFY01FaEFwUQ==",
  "took" : 1,
  "timed_out" : false,
  "terminated_early" : true,
  "_shards" : {
    "total" : 1,
    "successful" : 1,
    "skipped" : 0,
    "failed" : 0
  },
  "hits" : {
    "total" : {
      "value" : 10,
      "relation" : "eq"
    },
    "max_score" : null,
    "hits" : [
      {
        "_index" : "test_index",
        "_type" : "_doc",
        "_id" : "4",
        "_score" : null,
        "_source" : {
          "field1" : "four"
        },
        "sort" : [
          3
        ]
      },
      {
        "_index" : "test_index",
        "_type" : "_doc",
        "_id" : "5",
        "_score" : null,
        "_source" : {
          "field1" : "five"
        },
        "sort" : [
          4
        ]
      },
      {
        "_index" : "test_index",
        "_type" : "_doc",
        "_id" : "6",
        "_score" : null,
        "_source" : {
          "field1" : "six"
        },
        "sort" : [
          5
        ]
      }
    ]
  }
}

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