elasticsearch學習筆記（三十四）——Elasticsearch 基於scoll技術滾動搜索大量數據

在實際應用中，經過from+size不可避免會出現深分頁的瓶頸，那麼經過scoll技術就是一個很好的解決深分頁的方法。好比若是咱們一次性要查出10萬條數據，那麼使用from+size很顯然性能會很是的差，priority queue會很是的大。此時若是採用scroll滾動查詢，就能夠一批一批的查，直到全部數據都查詢完。

scroll原理

scoll搜索會在第一次搜索的時候，保存一個當時的視圖快照，以後只會基於該舊的視圖快照提供數據搜索，若是這個期間數據變動，是不會讓用戶看到的。並且ES內部是基於_doc進行排序的方式，性能較高。
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
        ]
      }
    ]
  }
}