01. 數(shù)據(jù)準(zhǔn)備

ElasticSearch 向 my_index 索引中索引了 12 條文檔：

PUT /my_index/_doc/1
{
  "title": "文雅酒店",
  "content": "青島",
  "price": 556
}

PUT /my_index/_doc/2
{
  "title": "金都嘉怡假日酒店",
  "content": "北京",
  "price": 337
}

PUT /my_index/_doc/3
{
  "title": "金都欣欣酒店",
  "content": "天津",
  "price": 200
}

PUT /my_index/_doc/4
{
  "title": "金都酒店",
  "content": "上海",
  "price": 300
}

PUT /my_index/_doc/5
{
  "title": "自如酒店",
  "content": "南京",
  "price": 400
}

PUT /my_index/_doc/6
{
  "title": "如家酒店",
  "content": "杭州",
  "price": 500
}


PUT /my_index/_doc/7
{
  "title": "非常酒店",
  "content": "合肥",
  "price": 600
}


PUT /my_index/_doc/8
{
  "title": "金都酒店",
  "content": "淮北",
  "price": 700
}

PUT /my_index/_doc/9
{
  "title": "金都酒店",
  "content": "淮南",
  "price": 900
}

PUT /my_index/_doc/10
{
  "title": "麗舍酒店",
  "content": "阜陽(yáng)",
  "price": 1000
}

PUT /my_index/_doc/11
{
  "title": "文軒酒店",
  "content": "蚌埠",
  "price": 1020
}

PUT /my_index/_doc/12
{
  "title": "大理酒店",
  "content": "長(zhǎng)沙",
  "price": 1100
}

02. ElasticSearch 如何查詢所有文檔？

ElasticSearch 查詢所有文檔

GET /my_index/_search

根據(jù)查詢結(jié)果可以看出，集群中總共有12個(gè)文檔，hits.total.value=12， 但是在 hits 數(shù)組中只有 10 個(gè)文檔。如何才能看到其他的文檔？

{
  "took" : 688,
  "timed_out" : false,
  "_shards" : {
    "total" : 1,
    "successful" : 1,
    "skipped" : 0,
    "failed" : 0
  },
  "hits" : {
    "total" : {
      "value" : 12,
      "relation" : "eq"
    },
    "max_score" : 1.0,
    "hits" : [
      {
        "_index" : "my_index",
        "_type" : "_doc",
        "_id" : "2",
        "_score" : 1.0,
        "_source" : {
          "title" : "金都嘉怡假日酒店",
          "content" : "北京",
          "price" : 337
        }
      },
      {
        "_index" : "my_index",
        "_type" : "_doc",
        "_id" : "3",
        "_score" : 1.0,
        "_source" : {
          "title" : "金都欣欣酒店",
          "content" : "天津",
          "price" : 200
        }
      },
      {
        "_index" : "my_index",
        "_type" : "_doc",
        "_id" : "1",
        "_score" : 1.0,
        "_source" : {
          "title" : "文雅酒店",
          "content" : "青島",
          "price" : 556
        }
      },
      {
        "_index" : "my_index",
        "_type" : "_doc",
        "_id" : "4",
        "_score" : 1.0,
        "_source" : {
          "title" : "金都酒店",
          "content" : "上海",
          "price" : 300
        }
      },
      {
        "_index" : "my_index",
        "_type" : "_doc",
        "_id" : "5",
        "_score" : 1.0,
        "_source" : {
          "title" : "自如酒店",
          "content" : "南京",
          "price" : 400
        }
      },
      {
        "_index" : "my_index",
        "_type" : "_doc",
        "_id" : "6",
        "_score" : 1.0,
        "_source" : {
          "title" : "如家酒店",
          "content" : "杭州",
          "price" : 500
        }
      },
      {
        "_index" : "my_index",
        "_type" : "_doc",
        "_id" : "7",
        "_score" : 1.0,
        "_source" : {
          "title" : "非常酒店",
          "content" : "合肥",
          "price" : 600
        }
      },
      {
        "_index" : "my_index",
        "_type" : "_doc",
        "_id" : "8",
        "_score" : 1.0,
        "_source" : {
          "title" : "金都酒店",
          "content" : "淮北",
          "price" : 700
        }
      },
      {
        "_index" : "my_index",
        "_type" : "_doc",
        "_id" : "9",
        "_score" : 1.0,
        "_source" : {
          "title" : "金都酒店",
          "content" : "淮南",
          "price" : 900
        }
      },
      {
        "_index" : "my_index",
        "_type" : "_doc",
        "_id" : "10",
        "_score" : 1.0,
        "_source" : {
          "title" : "麗舍酒店",
          "content" : "阜陽(yáng)",
          "price" : 1000
        }
      }
    ]
  }
}

03. ElasticSearch 如何指定搜索結(jié)果的條數(shù)？

Elasticsearch 接受 from 和 size 參數(shù)：

from：顯示應(yīng)該跳過(guò)的初始結(jié)果數(shù)量，默認(rèn)是0
size：顯示應(yīng)該返回的結(jié)果數(shù)量，默認(rèn)是10

from 和 size 參數(shù)的默認(rèn)值分別為 0 和 10，因此如果不指定這兩個(gè)參數(shù)，將返回前 10 條記錄，這也是為什么集群中總共有12個(gè)文檔，hits.total.value=12， 但是在 hits 數(shù)組中只有 10 個(gè)文檔的原因。

如果我們想返回更多的結(jié)果數(shù)量，可以通過(guò)size參數(shù)來(lái)指定：

GET /my_index/_search
{
  "size": 15
}

集群中總共有12條文檔。size=15 會(huì)把集群中所有的文檔返回：

{
  "took" : 0,
  "timed_out" : false,
  "_shards" : {
    "total" : 1,
    "successful" : 1,
    "skipped" : 0,
    "failed" : 0
  },
  "hits" : {
    "total" : {
      "value" : 12,
      "relation" : "eq"
    },
    "max_score" : 1.0,
    "hits" : [
      {
        "_index" : "my_index",
        "_type" : "_doc",
        "_id" : "2",
        "_score" : 1.0,
        "_source" : {
          "title" : "金都嘉怡假日酒店",
          "content" : "北京",
          "price" : 337
        }
      },
      {
        "_index" : "my_index",
        "_type" : "_doc",
        "_id" : "3",
        "_score" : 1.0,
        "_source" : {
          "title" : "金都欣欣酒店",
          "content" : "天津",
          "price" : 200
        }
      },
      {
        "_index" : "my_index",
        "_type" : "_doc",
        "_id" : "1",
        "_score" : 1.0,
        "_source" : {
          "title" : "文雅酒店",
          "content" : "青島",
          "price" : 556
        }
      },
      {
        "_index" : "my_index",
        "_type" : "_doc",
        "_id" : "4",
        "_score" : 1.0,
        "_source" : {
          "title" : "金都酒店",
          "content" : "上海",
          "price" : 300
        }
      },
      {
        "_index" : "my_index",
        "_type" : "_doc",
        "_id" : "5",
        "_score" : 1.0,
        "_source" : {
          "title" : "自如酒店",
          "content" : "南京",
          "price" : 400
        }
      },
      {
        "_index" : "my_index",
        "_type" : "_doc",
        "_id" : "6",
        "_score" : 1.0,
        "_source" : {
          "title" : "如家酒店",
          "content" : "杭州",
          "price" : 500
        }
      },
      {
        "_index" : "my_index",
        "_type" : "_doc",
        "_id" : "7",
        "_score" : 1.0,
        "_source" : {
          "title" : "非常酒店",
          "content" : "合肥",
          "price" : 600
        }
      },
      {
        "_index" : "my_index",
        "_type" : "_doc",
        "_id" : "8",
        "_score" : 1.0,
        "_source" : {
          "title" : "金都酒店",
          "content" : "淮北",
          "price" : 700
        }
      },
      {
        "_index" : "my_index",
        "_type" : "_doc",
        "_id" : "9",
        "_score" : 1.0,
        "_source" : {
          "title" : "金都酒店",
          "content" : "淮南",
          "price" : 900
        }
      },
      {
        "_index" : "my_index",
        "_type" : "_doc",
        "_id" : "10",
        "_score" : 1.0,
        "_source" : {
          "title" : "麗舍酒店",
          "content" : "阜陽(yáng)",
          "price" : 1000
        }
      },
      {
        "_index" : "my_index",
        "_type" : "_doc",
        "_id" : "11",
        "_score" : 1.0,
        "_source" : {
          "title" : "文軒酒店",
          "content" : "蚌埠",
          "price" : 1020
        }
      },
      {
        "_index" : "my_index",
        "_type" : "_doc",
        "_id" : "12",
        "_score" : 1.0,
        "_source" : {
          "title" : "大理酒店",
          "content" : "長(zhǎng)沙",
          "price" : 1100
        }
      }
    ]
  }
}

04. ElasticSearch 分頁(yè)查詢方式有哪些？

使用 from 和 size 參數(shù)來(lái)實(shí)現(xiàn)分頁(yè)查詢。
使用 scroll 查詢來(lái)實(shí)現(xiàn)分頁(yè)查詢。
使用搜索后再次查詢的方式來(lái)實(shí)現(xiàn)分頁(yè)查詢。

05. ElasticSearch 如何實(shí)現(xiàn) from+size 分頁(yè)查詢？

在 ElasticSearch 中，可以使用 from 和 size 參數(shù)來(lái)進(jìn)行分頁(yè)搜索。 from 和 size 參數(shù)用來(lái)指定從哪個(gè)文檔開始，返回多少個(gè)文檔。具體命令如下：

GET /my_index/_search
{
  "query": {
    "match": {
      "title": "酒店"
    }
  }, 
  "from": 0, // 從第 1 條數(shù)據(jù)開始
  "size": 3  // 返回 3 條數(shù)據(jù)
}

結(jié)果如下，總共有12條數(shù)據(jù)，從第1條數(shù)據(jù)開始，返回3條數(shù)據(jù)：

{
  "took" : 19,
  "timed_out" : false,
  "_shards" : {
    "total" : 1,
    "successful" : 1,
    "skipped" : 0,
    "failed" : 0
  },
  "hits" : {
    "total" : {
      "value" : 12,
      "relation" : "eq"
    },
    "max_score" : 0.075949445,
    "hits" : [
      {
        "_index" : "my_index",
        "_type" : "_doc",
        "_id" : "1",
        "_score" : 0.075949445,
        "_source" : {
          "title" : "文雅酒店",
          "content" : "青島",
          "price" : 556
        }
      },
      {
        "_index" : "my_index",
        "_type" : "_doc",
        "_id" : "4",
        "_score" : 0.075949445,
        "_source" : {
          "title" : "金都酒店",
          "content" : "上海",
          "price" : 300
        }
      },
      {
        "_index" : "my_index",
        "_type" : "_doc",
        "_id" : "5",
        "_score" : 0.075949445,
        "_source" : {
          "title" : "自如酒店",
          "content" : "南京",
          "price" : 400
        }
      }
    ]
  }
}

在上面的命令中，我們使用 from 參數(shù)指定從哪個(gè)文檔開始，使用 size 參數(shù)指定返回多少個(gè)文檔。例如，當(dāng) from=0 且 size=10 時(shí)，返回的是第 1 到第 10 條數(shù)據(jù)。當(dāng) from=10 且 size=10 時(shí)，返回的是第 11 到第 20 條數(shù)據(jù)。

06. ElasticSearch 如何實(shí)現(xiàn) searchAfter 分頁(yè)查詢？

Search After API 可以用于在 Elasticsearch 中處理大量數(shù)據(jù)。它允許您在不影響性能的情況下檢索大量數(shù)據(jù)。使用 Search After API，您可以在多個(gè)請(qǐng)求之間保持查詢上下文，并在每個(gè)請(qǐng)求中返回一定數(shù)量的結(jié)果。這樣，您就可以逐步處理大量數(shù)據(jù)，而不必一次性將所有數(shù)據(jù)加載到內(nèi)存中。

Search After API 從指定的某個(gè)數(shù)據(jù)后面開始讀。這種方式不能隨機(jī)跳轉(zhuǎn)分頁(yè)，只能一頁(yè)一頁(yè)地讀取數(shù)據(jù)，而且必須用一個(gè)唯一且不重復(fù)的屬性對(duì)查詢數(shù)據(jù)進(jìn)行排序。

POST /my_index/_search
{
  "size": 3,
  "query": {
    "match": {
      "title": "酒店"
    }
  },
  "sort": [
    {
      "price": "asc"
    }
  ],
  "track_total_hits": true
}

以上代碼表示從 my_index 索引中查詢 title 包含 酒店的數(shù)據(jù)，每次返回 3 條數(shù)據(jù)，并按照 price 字段升序排序。查詢結(jié)果中會(huì)返回一個(gè) sort 值，用于在后續(xù)請(qǐng)求中使用。同時(shí)，設(shè)置 track_total_hits 參數(shù)為 true，表示計(jì)算總命中數(shù)。

查詢文檔的總命中數(shù) hits.total.value 為12，返回3條數(shù)據(jù)：

{
  "took" : 3,
  "timed_out" : false,
  "_shards" : {
    "total" : 1,
    "successful" : 1,
    "skipped" : 0,
    "failed" : 0
  },
  "hits" : {
    "total" : {
      "value" : 12,
      "relation" : "eq"
    },
    "max_score" : null,
    "hits" : [
      {
        "_index" : "my_index",
        "_type" : "_doc",
        "_id" : "3",
        "_score" : null,
        "_source" : {
          "title" : "金都欣欣酒店",
          "content" : "天津",
          "price" : 200
        },
        "sort" : [
          200
        ]
      },
      {
        "_index" : "my_index",
        "_type" : "_doc",
        "_id" : "4",
        "_score" : null,
        "_source" : {
          "title" : "金都酒店",
          "content" : "上海",
          "price" : 300
        },
        "sort" : [
          300
        ]
      },
      {
        "_index" : "my_index",
        "_type" : "_doc",
        "_id" : "2",
        "_score" : null,
        "_source" : {
          "title" : "金都嘉怡假日酒店",
          "content" : "北京",
          "price" : 337
        },
        "sort" : [
          337
        ]
      }
    ]
  }
}

接下來(lái)，可以使用 sort 值來(lái)獲取下一頁(yè)數(shù)據(jù)：

POST /my_index/_search
{
  "size": 1000,
  "query": {
    "match": {
      "title": "酒店"
    }
  },
  "sort": [
    {
      "price": "asc"
    }
  ],
  "search_after": [337]
}

{
  "took" : 4,
  "timed_out" : false,
  "_shards" : {
    "total" : 1,
    "successful" : 1,
    "skipped" : 0,
    "failed" : 0
  },
  "hits" : {
    "total" : {
      "value" : 12,
      "relation" : "eq"
    },
    "max_score" : null,
    "hits" : [
      {
        "_index" : "my_index",
        "_type" : "_doc",
        "_id" : "5",
        "_score" : null,
        "_source" : {
          "title" : "自如酒店",
          "content" : "南京",
          "price" : 400
        },
        "sort" : [
          400
        ]
      },
      {
        "_index" : "my_index",
        "_type" : "_doc",
        "_id" : "6",
        "_score" : null,
        "_source" : {
          "title" : "如家酒店",
          "content" : "杭州",
          "price" : 500
        },
        "sort" : [
          500
        ]
      },
      {
        "_index" : "my_index",
        "_type" : "_doc",
        "_id" : "1",
        "_score" : null,
        "_source" : {
          "title" : "文雅酒店",
          "content" : "青島",
          "price" : 556
        },
        "sort" : [
          556
        ]
      }
    ]
  }
}

07. ElasticSearch 如何實(shí)現(xiàn) scroll 分頁(yè)查詢？

Scroll API 可以用于在 Elasticsearch 中處理大量數(shù)據(jù)。它允許您在不影響性能的情況下檢索大量數(shù)據(jù)。使用 Scroll API，您可以在多個(gè)請(qǐng)求之間保持查詢上下文，并在每個(gè)請(qǐng)求中返回一定數(shù)量的結(jié)果。這樣，您就可以逐步處理大量數(shù)據(jù)，而不必一次性將所有數(shù)據(jù)加載到內(nèi)存中。

第一個(gè)查詢會(huì)在內(nèi)存中保存一個(gè)歷史快照和光標(biāo)（scroll_id）來(lái)記錄當(dāng)前消息查詢的終止位置。下次查詢會(huì)從光標(biāo)記錄的位置往后進(jìn)行查詢。這種方式性能好，一般用于海量數(shù)據(jù)導(dǎo)出或者重建索引。但是 scroll_id 有過(guò)期時(shí)間，兩次查詢之間如果 scroll_id 過(guò)期了，第二次查詢會(huì)拋異?！罢也坏?“scroll_id”。

啟用游標(biāo)查詢可以通過(guò)在查詢的時(shí)候設(shè)置參數(shù) scroll 的值為我們期望的游標(biāo)查詢的過(guò)期時(shí)間。 游標(biāo)查詢的過(guò)期時(shí)間會(huì)在每次做查詢的時(shí)候刷新，所以這個(gè)時(shí)間只需要足夠處理當(dāng)前批的結(jié)果就可以了，而不是處理查詢結(jié)果的所有文檔的所需時(shí)間。 這個(gè)過(guò)期時(shí)間的參數(shù)很重要，因?yàn)楸３诌@個(gè)游標(biāo)查詢窗口需要消耗資源，所以我們期望如果不再需要維護(hù)這種資源就該早點(diǎn)兒釋放掉。 設(shè)置這個(gè)超時(shí)能夠讓 Elasticsearch 在稍后空閑的時(shí)候自動(dòng)釋放這部分資源。

① 執(zhí)行初始查詢，獲取scroll_id，其中，scroll參數(shù)指定了scroll查詢的有效時(shí)間，這里設(shè)置為1分鐘，size 表示每次返回7條數(shù)據(jù)。

POST /my_index/_search?scroll=1m
{
  "size": 7,
  "query": {
    "match": {
      "title": "酒店"
    }
  }
}

執(zhí)行上述查詢后，查詢結(jié)果中會(huì)返回一個(gè) scroll_id，用于在后續(xù)請(qǐng)求中使用，類似于以下內(nèi)容：

{
  "_scroll_id" : "DXF1ZXJ5QW5kRmV0Y2gBAAAAAAACQVUWZFFwRElpblJROU9lZV9LeXI5MUpPQQ==",
  "took" : 0,
  "timed_out" : false,
  "_shards" : {
    "total" : 1,
    "successful" : 1,
    "skipped" : 0,
    "failed" : 0
  },
  "hits" : {
    "total" : {
      "value" : 12,
      "relation" : "eq"
    },
    "max_score" : 0.06382885,
    "hits" : [
      {
        "_index" : "my_index",
        "_type" : "_doc",
        "_id" : "1",
        "_score" : 0.06382885,
        "_source" : {
          "title" : "文雅酒店",
          "content" : "青島",
          "price" : 556
        }
      },
      {
        "_index" : "my_index",
        "_type" : "_doc",
        "_id" : "4",
        "_score" : 0.06382885,
        "_source" : {
          "title" : "金都酒店",
          "content" : "上海",
          "price" : 300
        }
      },
      {
        "_index" : "my_index",
        "_type" : "_doc",
        "_id" : "5",
        "_score" : 0.06382885,
        "_source" : {
          "title" : "自如酒店",
          "content" : "南京",
          "price" : 400
        }
      },
      {
        "_index" : "my_index",
        "_type" : "_doc",
        "_id" : "6",
        "_score" : 0.06382885,
        "_source" : {
          "title" : "如家酒店",
          "content" : "杭州",
          "price" : 500
        }
      },
      {
        "_index" : "my_index",
        "_type" : "_doc",
        "_id" : "7",
        "_score" : 0.06382885,
        "_source" : {
          "title" : "非常酒店",
          "content" : "合肥",
          "price" : 600
        }
      },
      {
        "_index" : "my_index",
        "_type" : "_doc",
        "_id" : "9",
        "_score" : 0.06382885,
        "_source" : {
          "title" : "金都酒店",
          "content" : "淮南",
          "price" : 900
        }
      },
      {
        "_index" : "my_index",
        "_type" : "_doc",
        "_id" : "8",
        "_score" : 0.06382885,
        "_source" : {
          "title" : "金都酒店",
          "content" : "淮北",
          "price" : 700
        }
      }
    ]
  }
}

② 使用scroll_id獲取下一頁(yè)數(shù)據(jù)：

POST /_search/scroll
{
  "scroll": "1m",
  "scroll_id": "DXF1ZXJ5QW5kRmV0Y2gBAAAAAAACQVUWZFFwRElpblJROU9lZV9LeXI5MUpPQQ=="
}

執(zhí)行上述查詢后，會(huì)返回下一頁(yè)數(shù)據(jù)和一個(gè)新的scroll_id：

{
  "_scroll_id" : "DXF1ZXJ5QW5kRmV0Y2gBAAAAAAACQVUWZFFwRElpblJROU9lZV9LeXI5MUpPQQ==",
  "took" : 4,
  "timed_out" : false,
  "_shards" : {
    "total" : 1,
    "successful" : 1,
    "skipped" : 0,
    "failed" : 0
  },
  "hits" : {
    "total" : {
      "value" : 12,
      "relation" : "eq"
    },
    "max_score" : 0.06382885,
    "hits" : [
      {
        "_index" : "my_index",
        "_type" : "_doc",
        "_id" : "10",
        "_score" : 0.06382885,
        "_source" : {
          "title" : "麗舍酒店",
          "content" : "阜陽(yáng)",
          "price" : 1000,
          "uploadTime" : 1678073241
        }
      },
      {
        "_index" : "my_index",
        "_type" : "_doc",
        "_id" : "11",
        "_score" : 0.06382885,
        "_source" : {
          "title" : "文軒酒店",
          "content" : "蚌埠",
          "price" : 1020
        }
      },
      {
        "_index" : "my_index",
        "_type" : "_doc",
        "_id" : "12",
        "_score" : 0.06382885,
        "_source" : {
          "title" : "大理酒店",
          "content" : "長(zhǎng)沙",
          "price" : 1100
        }
      },
      {
        "_index" : "my_index",
        "_type" : "_doc",
        "_id" : "3",
        "_score" : 0.05390298,
        "_source" : {
          "title" : "金都欣欣酒店",
          "content" : "天津",
          "price" : 200
        }
      },
      {
        "_index" : "my_index",
        "_type" : "_doc",
        "_id" : "2",
        "_score" : 0.046648744,
        "_source" : {
          "title" : "金都嘉怡假日酒店",
          "content" : "北京",
          "price" : 337
        }
      }
    ]
  }
}

③ 重復(fù)步驟②，直到所有數(shù)據(jù)都被檢索完畢

POST /_search/scroll
{
  "scroll": "1m",
  "scroll_id": "DXF1ZXJ5QW5kRmV0Y2gBAAAAAAACQVUWZFFwRElpblJROU9lZV9LeXI5MUpPQQ=="
}

{
  "_scroll_id" : "DXF1ZXJ5QW5kRmV0Y2gBAAAAAAACQVUWZFFwRElpblJROU9lZV9LeXI5MUpPQQ==",
  "took" : 1,
  "timed_out" : false,
  "_shards" : {
    "total" : 1,
    "successful" : 1,
    "skipped" : 0,
    "failed" : 0
  },
  "hits" : {
    "total" : {
      "value" : 12,
      "relation" : "eq"
    },
    "max_score" : 0.06382885,
    "hits" : [ ]
  }
}

④ 當(dāng)所有數(shù)據(jù)都被檢索完畢后，需要使用clear_scroll API來(lái)清除scroll_id。

DELETE /_search/scroll
{
    "scroll_id": [
        "DXF1ZXJ5QW5kRmV0Y2gBAAAAAAACQVUWZFFwRElpblJROU9lZV9LeXI5MUpPQQ==",
        "DXF1ZXJ5QW5kRmV0Y2gBAAAAAAACQVUWZFFwRElpblJROU9lZV9LeXI5MUpPQQ=="
    ]
}

注意，scroll查詢會(huì)占用Elasticsearch的資源，因此在使用時(shí)需要注意性能問(wèn)題。同時(shí)，scroll查詢也不適用于實(shí)時(shí)數(shù)據(jù)的查詢，因?yàn)閟croll查詢只能查詢到在scroll查詢開始時(shí)已經(jīng)存在的數(shù)據(jù)。

08. ElasticSearch 深分頁(yè)是什么？

ElasticSearch 深分頁(yè)是指在搜索結(jié)果中，需要跳過(guò)大量的文檔才能到達(dá)目標(biāo)文檔的情況。這種情況通常發(fā)生在需要訪問(wèn)大量文檔的搜索結(jié)果中，例如搜索結(jié)果有數(shù)百萬(wàn)個(gè)文檔，但只需要訪問(wèn)其中的前幾個(gè)文檔。這個(gè)查詢的實(shí)現(xiàn)原理類似于mysql中的limit。比如查詢10001條數(shù)據(jù)，需要把前10000條取出來(lái)過(guò)濾，最后得到數(shù)據(jù)。

在 ElasticSearch 中，深分頁(yè)可能會(huì)導(dǎo)致性能問(wèn)題，因?yàn)槊看翁^(guò)大量文檔時(shí)，ElasticSearch 都需要執(zhí)行一次查詢，并且需要將查詢結(jié)果中的所有文檔加載到內(nèi)存中，這會(huì)占用大量的 CPU 和內(nèi)存資源。

為了避免這種情況，可以使用 ElasticSearch 的 Scroll API 或 Search After API 來(lái)進(jìn)行分頁(yè)查詢。這些 API 可以在不加載所有文檔的情況下，快速地獲取搜索結(jié)果中的指定文檔。

09. ElasticSearch 分頁(yè)查詢的最大限制是多少？

當(dāng)查詢頁(yè)很深或者查詢的數(shù)據(jù)量很大時(shí)，就會(huì)發(fā)生深分頁(yè)。ElasticSearch 分頁(yè)查詢的最大限制是 10000 條數(shù)據(jù)，當(dāng)查詢條數(shù)超過(guò)10000時(shí)，會(huì)報(bào)錯(cuò)。

GET /my_index/_search
{
  "query": {
    "match": {
      "title": "酒店"
    }
  }, 
  "from": 0,
  "size": 10001
}

查詢結(jié)果會(huì)報(bào)錯(cuò)：Result window is too large, from + size must be less than or equal to: [10000] but was [10001]. See the scroll api for a more efficient way to request large data sets. This limit can be set by changing the [index.max_result_window] index level setting.

也就是說(shuō)我們最多只能分頁(yè)查詢10000條數(shù)據(jù)。

10. ElasticSearch 如何解除分頁(yè)查詢的限制？

max_result_window 屬性控制從Elasticsearch中檢索文檔的最大數(shù)量，默認(rèn)情況下，它的值為10000?？梢酝ㄟ^(guò)修改 index.max_result_window 參數(shù)來(lái)增加搜索結(jié)果的最大數(shù)量。如果您需要檢索更多的文檔，請(qǐng)?jiān)黾觤ax_result_window的值。但是，需要注意的是，增加max_result_window的值可能會(huì)影響Elasticsearch的性能。

第一種辦法：在kibana中執(zhí)行，解除索引最大查詢數(shù)的限制

PUT /my_index/_settings
{
  "index.max_result_window":200000
}

第二種辦法：在創(chuàng)建索引的時(shí)候加上

PUT /my_index
{
  "settings": {
    "index": {
      "max_result_window": 10000
    }
  }
}

11. ElasticSearch 查詢文檔總命中數(shù)最大限制為多少？

ElasticSearch中可以根據(jù)搜索結(jié)果中的 hits.total.value 值獲取查詢文檔的總命中數(shù)， 但最大返回條數(shù)是有限制的，默認(rèn)情況下最大為 10000 條。數(shù)據(jù)量不大的情況下這個(gè)數(shù)值沒問(wèn)題。但是當(dāng)數(shù)據(jù)超出 10000 的時(shí)候，這個(gè) hits.total.value 將不會(huì)增長(zhǎng)了，固定為 10000，這個(gè)時(shí)候的匹配文檔數(shù)量統(tǒng)計(jì)就不準(zhǔn)了。

如集群中總共有30000條文檔，查詢所有時(shí) hits.total.value 的值卻為10000：

{
  "took" : 1,
  "timed_out" : false,
  "_shards" : {
    "total" : 1,
    "successful" : 1,
    "skipped" : 0,
    "failed" : 0
  },
  "hits" : {
    "total" : {
      "value" : 10000,
      "relation" : "eq"
    },
    "max_score" : null,
    "hits" : [
        // ...
     ]
  }
}

12. ElasticSearch 如何解除查詢文檔總命中數(shù)的限制？

Elasticsearch 的 track_total_hits 參數(shù)用于控制查詢時(shí)是否計(jì)算總命中數(shù)，如果想要統(tǒng)計(jì)準(zhǔn)確的匹配文檔數(shù)，需要使用參數(shù) track_total_hits 來(lái)開啟精確匹配。默認(rèn)情況下會(huì)計(jì)算前10000條數(shù)據(jù)的總命中數(shù)，如果想解除這個(gè)限制，需要將track_total_hits 參數(shù)設(shè)置為true。

track_total_hits 參數(shù)有三種取值：

true：計(jì)算總命中數(shù)。
false：不計(jì)算總命中數(shù)。
數(shù)字：只計(jì)算前 n 條數(shù)據(jù)的總命中數(shù)。

① 計(jì)算總命中數(shù)：

GET /my_index/_search
{
  "query": {
    "match": {
      "title": "酒店"
    }
  },
  "track_total_hits": true
}

查詢文檔的總命中數(shù) hits.total.value 值為12，文檔列表 hits.hits 中10條文檔（from=0，size=10）

{
  "took" : 3,
  "timed_out" : false,
  "_shards" : {
    "total" : 1,
    "successful" : 1,
    "skipped" : 0,
    "failed" : 0
  },
  "hits" : {
    "total" : {
      "value" : 12,
      "relation" : "eq"
    },
    "max_score" : 0.06382885,
    "hits" : [
      {
        "_index" : "my_index",
        "_type" : "_doc",
        "_id" : "1",
        "_score" : 0.06382885,
        "_source" : {
          "title" : "文雅酒店",
          "content" : "青島",
          "price" : 556
        }
      },
      {
        "_index" : "my_index",
        "_type" : "_doc",
        "_id" : "4",
        "_score" : 0.06382885,
        "_source" : {
          "title" : "金都酒店",
          "content" : "上海",
          "price" : 300
        }
      },
      {
        "_index" : "my_index",
        "_type" : "_doc",
        "_id" : "5",
        "_score" : 0.06382885,
        "_source" : {
          "title" : "自如酒店",
          "content" : "南京",
          "price" : 400
        }
      },
      {
        "_index" : "my_index",
        "_type" : "_doc",
        "_id" : "6",
        "_score" : 0.06382885,
        "_source" : {
          "title" : "如家酒店",
          "content" : "杭州",
          "price" : 500
        }
      },
      {
        "_index" : "my_index",
        "_type" : "_doc",
        "_id" : "7",
        "_score" : 0.06382885,
        "_source" : {
          "title" : "非常酒店",
          "content" : "合肥",
          "price" : 600
        }
      },
      {
        "_index" : "my_index",
        "_type" : "_doc",
        "_id" : "9",
        "_score" : 0.06382885,
        "_source" : {
          "title" : "金都酒店",
          "content" : "淮南",
          "price" : 900
        }
      },
      {
        "_index" : "my_index",
        "_type" : "_doc",
        "_id" : "8",
        "_score" : 0.06382885,
        "_source" : {
          "title" : "金都酒店",
          "content" : "淮北",
          "price" : 700
        }
      },
      {
        "_index" : "my_index",
        "_type" : "_doc",
        "_id" : "10",
        "_score" : 0.06382885,
        "_source" : {
          "title" : "麗舍酒店",
          "content" : "阜陽(yáng)",
          "price" : 1000,
          "uploadTime" : 1678073241
        }
      },
      {
        "_index" : "my_index",
        "_type" : "_doc",
        "_id" : "11",
        "_score" : 0.06382885,
        "_source" : {
          "title" : "文軒酒店",
          "content" : "蚌埠",
          "price" : 1020
        }
      },
      {
        "_index" : "my_index",
        "_type" : "_doc",
        "_id" : "12",
        "_score" : 0.06382885,
        "_source" : {
          "title" : "大理酒店",
          "content" : "長(zhǎng)沙",
          "price" : 1100
        }
      }
    ]
  }
}

② 不計(jì)算總命中數(shù)：

GET /my_index/_search
{
  "query": {
    "match": {
      "title": "酒店"
    }
  },
  "track_total_hits": false
}

查詢結(jié)果中不返回總命中數(shù) hits.total.value ，文檔列表 hits.hits 中10條文檔（from=0，size=10）

{
  "took" : 8,
  "timed_out" : false,
  "_shards" : {
    "total" : 1,
    "successful" : 1,
    "skipped" : 0,
    "failed" : 0
  },
  "hits" : {
    "max_score" : 0.06382885,
    "hits" : [
      {
        "_index" : "my_index",
        "_type" : "_doc",
        "_id" : "1",
        "_score" : 0.06382885,
        "_source" : {
          "title" : "文雅酒店",
          "content" : "青島",
          "price" : 556
        }
      },
      {
        "_index" : "my_index",
        "_type" : "_doc",
        "_id" : "4",
        "_score" : 0.06382885,
        "_source" : {
          "title" : "金都酒店",
          "content" : "上海",
          "price" : 300
        }
      },
      {
        "_index" : "my_index",
        "_type" : "_doc",
        "_id" : "5",
        "_score" : 0.06382885,
        "_source" : {
          "title" : "自如酒店",
          "content" : "南京",
          "price" : 400
        }
      },
      {
        "_index" : "my_index",
        "_type" : "_doc",
        "_id" : "6",
        "_score" : 0.06382885,
        "_source" : {
          "title" : "如家酒店",
          "content" : "杭州",
          "price" : 500
        }
      },
      {
        "_index" : "my_index",
        "_type" : "_doc",
        "_id" : "7",
        "_score" : 0.06382885,
        "_source" : {
          "title" : "非常酒店",
          "content" : "合肥",
          "price" : 600
        }
      },
      {
        "_index" : "my_index",
        "_type" : "_doc",
        "_id" : "9",
        "_score" : 0.06382885,
        "_source" : {
          "title" : "金都酒店",
          "content" : "淮南",
          "price" : 900
        }
      },
      {
        "_index" : "my_index",
        "_type" : "_doc",
        "_id" : "8",
        "_score" : 0.06382885,
        "_source" : {
          "title" : "金都酒店",
          "content" : "淮北",
          "price" : 700
        }
      },
      {
        "_index" : "my_index",
        "_type" : "_doc",
        "_id" : "10",
        "_score" : 0.06382885,
        "_source" : {
          "title" : "麗舍酒店",
          "content" : "阜陽(yáng)",
          "price" : 1000,
          "uploadTime" : 1678073241
        }
      },
      {
        "_index" : "my_index",
        "_type" : "_doc",
        "_id" : "11",
        "_score" : 0.06382885,
        "_source" : {
          "title" : "文軒酒店",
          "content" : "蚌埠",
          "price" : 1020
        }
      },
      {
        "_index" : "my_index",
        "_type" : "_doc",
        "_id" : "12",
        "_score" : 0.06382885,
        "_source" : {
          "title" : "大理酒店",
          "content" : "長(zhǎng)沙",
          "price" : 1100
        }
      }
    ]
  }
}

③ 只計(jì)算前5條數(shù)據(jù)的總命中數(shù)：

GET /my_index/_search
{
  "query": {
    "match": {
      "title": "酒店"
    }
  },
  "track_total_hits": 5
}

前5條數(shù)據(jù)的總命中數(shù) hits.total.value 值為5，文檔列表 hits.hits 中10條文檔（from=0，size=10）

{
  "took" : 1,
  "timed_out" : false,
  "_shards" : {
    "total" : 1,
    "successful" : 1,
    "skipped" : 0,
    "failed" : 0
  },
  "hits" : {
    "total" : {
      "value" : 5,
      "relation" : "gte"
    },
    "max_score" : 0.06382885,
    "hits" : [
      {
        "_index" : "my_index",
        "_type" : "_doc",
        "_id" : "1",
        "_score" : 0.06382885,
        "_source" : {
          "title" : "文雅酒店",
          "content" : "青島",
          "price" : 556
        }
      },
      {
        "_index" : "my_index",
        "_type" : "_doc",
        "_id" : "4",
        "_score" : 0.06382885,
        "_source" : {
          "title" : "金都酒店",
          "content" : "上海",
          "price" : 300
        }
      },
      {
        "_index" : "my_index",
        "_type" : "_doc",
        "_id" : "5",
        "_score" : 0.06382885,
        "_source" : {
          "title" : "自如酒店",
          "content" : "南京",
          "price" : 400
        }
      },
      {
        "_index" : "my_index",
        "_type" : "_doc",
        "_id" : "6",
        "_score" : 0.06382885,
        "_source" : {
          "title" : "如家酒店",
          "content" : "杭州",
          "price" : 500
        }
      },
      {
        "_index" : "my_index",
        "_type" : "_doc",
        "_id" : "7",
        "_score" : 0.06382885,
        "_source" : {
          "title" : "非常酒店",
          "content" : "合肥",
          "price" : 600
        }
      },
      {
        "_index" : "my_index",
        "_type" : "_doc",
        "_id" : "9",
        "_score" : 0.06382885,
        "_source" : {
          "title" : "金都酒店",
          "content" : "淮南",
          "price" : 900
        }
      },
      {
        "_index" : "my_index",
        "_type" : "_doc",
        "_id" : "8",
        "_score" : 0.06382885,
        "_source" : {
          "title" : "金都酒店",
          "content" : "淮北",
          "price" : 700
        }
      },
      {
        "_index" : "my_index",
        "_type" : "_doc",
        "_id" : "10",
        "_score" : 0.06382885,
        "_source" : {
          "title" : "麗舍酒店",
          "content" : "阜陽(yáng)",
          "price" : 1000,
          "uploadTime" : 1678073241
        }
      },
      {
        "_index" : "my_index",
        "_type" : "_doc",
        "_id" : "11",
        "_score" : 0.06382885,
        "_source" : {
          "title" : "文軒酒店",
          "content" : "蚌埠",
          "price" : 1020
        }
      },
      {
        "_index" : "my_index",
        "_type" : "_doc",
        "_id" : "12",
        "_score" : 0.06382885,
        "_source" : {
          "title" : "大理酒店",
          "content" : "長(zhǎng)沙",
          "price" : 1100
        }
      }
    ]
  }
}

④ 計(jì)算前15條文檔的總命中數(shù)：

GET /my_index/_search
{
  "query": {
    "match": {
      "title": "酒店"
    }
  },
  "track_total_hits": 15
}

前15條數(shù)據(jù)的總命中數(shù) hits.total.value 值為12，文檔列表 hits.hits 中10條文檔（from=0，size=10）

{
  "took" : 1,
  "timed_out" : false,
  "_shards" : {
    "total" : 1,
    "successful" : 1,
    "skipped" : 0,
    "failed" : 0
  },
  "hits" : {
    "total" : {
      "value" : 12,
      "relation" : "eq"
    },
    "max_score" : 0.06382885,
    "hits" : [
      {
        "_index" : "my_index",
        "_type" : "_doc",
        "_id" : "1",
        "_score" : 0.06382885,
        "_source" : {
          "title" : "文雅酒店",
          "content" : "青島",
          "price" : 556
        }
      },
      {
        "_index" : "my_index",
        "_type" : "_doc",
        "_id" : "4",
        "_score" : 0.06382885,
        "_source" : {
          "title" : "金都酒店",
          "content" : "上海",
          "price" : 300
        }
      },
      {
        "_index" : "my_index",
        "_type" : "_doc",
        "_id" : "5",
        "_score" : 0.06382885,
        "_source" : {
          "title" : "自如酒店",
          "content" : "南京",
          "price" : 400
        }
      },
      {
        "_index" : "my_index",
        "_type" : "_doc",
        "_id" : "6",
        "_score" : 0.06382885,
        "_source" : {
          "title" : "如家酒店",
          "content" : "杭州",
          "price" : 500
        }
      },
      {
        "_index" : "my_index",
        "_type" : "_doc",
        "_id" : "7",
        "_score" : 0.06382885,
        "_source" : {
          "title" : "非常酒店",
          "content" : "合肥",
          "price" : 600
        }
      },
      {
        "_index" : "my_index",
        "_type" : "_doc",
        "_id" : "9",
        "_score" : 0.06382885,
        "_source" : {
          "title" : "金都酒店",
          "content" : "淮南",
          "price" : 900
        }
      },
      {
        "_index" : "my_index",
        "_type" : "_doc",
        "_id" : "8",
        "_score" : 0.06382885,
        "_source" : {
          "title" : "金都酒店",
          "content" : "淮北",
          "price" : 700
        }
      },
      {
        "_index" : "my_index",
        "_type" : "_doc",
        "_id" : "10",
        "_score" : 0.06382885,
        "_source" : {
          "title" : "麗舍酒店",
          "content" : "阜陽(yáng)",
          "price" : 1000,
          "uploadTime" : 1678073241
        }
      },
      {
        "_index" : "my_index",
        "_type" : "_doc",
        "_id" : "11",
        "_score" : 0.06382885,
        "_source" : {
          "title" : "文軒酒店",
          "content" : "蚌埠",
          "price" : 1020
        }
      },
      {
        "_index" : "my_index",
        "_type" : "_doc",
        "_id" : "12",
        "_score" : 0.06382885,
        "_source" : {
          "title" : "大理酒店",
          "content" : "長(zhǎng)沙",
          "price" : 1100
        }
      }
    ]
  }
}

13. ElasticSearch 分頁(yè)查詢的性能優(yōu)化有哪些？

盡量減少查詢的字段，只查詢需要的字段。
盡量減少查詢的數(shù)據(jù)量，只查詢需要的數(shù)據(jù)。
使用 scroll 查詢或者搜索后再次查詢的方式來(lái)避免過(guò)多的分頁(yè)查詢。
使用索引優(yōu)化技術(shù)，如分片、副本等來(lái)提高查詢性能。文章來(lái)源地址http://www.zghlxwxcb.cn/news/detail-401588.html

14. SpringBoo整合ES實(shí)現(xiàn)：from+size 分頁(yè)查詢？

GET /my_index/_search
{
  "query": {
    "match": {
      "title": "酒店"
    }
  }, 
  "from": 0, // 從第 1 條數(shù)據(jù)開始
  "size": 3  // 返回 3 條數(shù)據(jù)
}

@Slf4j
@Service
public class ElasticSearchImpl {

    @Autowired
    private RestHighLevelClient restHighLevelClient;

    public void searchUser() throws IOException {
        SearchSourceBuilder searchSourceBuilder = new SearchSourceBuilder();
        // query 查詢
        MatchQueryBuilder matchQueryBuilder = new MatchQueryBuilder("title","酒店");
        searchSourceBuilder.query(matchQueryBuilder);
        
        // 分頁(yè)查詢
        int page = 1; // 第1頁(yè)
        int pageSize = 3; // 每頁(yè)返回3條數(shù)據(jù)
        searchSourceBuilder.from((page-1)*pageSize);
        searchSourceBuilder.size(pageSize);

        SearchRequest searchRequest = new SearchRequest(new String[]{"my_index"},searchSourceBuilder);
        SearchResponse searchResponse = restHighLevelClient.search(searchRequest, RequestOptions.DEFAULT);

        // 搜索結(jié)果
        SearchHits searchHits = searchResponse.getHits();
        SearchHit[] hits = searchHits.getHits();
        for (SearchHit hit : hits) {
            // hits.hits._source：匹配的文檔的原始數(shù)據(jù)
            String sourceAsString = hit.getSourceAsString();
        }
        System.out.println(searchResponse);

    }
}

15. SpringBoo整合ES實(shí)現(xiàn)：searchAfetr 分頁(yè)查詢？

POST /my_index/_search
{
  "size": 3,
  "query": {
    "match": {
      "title": "酒店"
    }
  },
  "sort": [
    {
      "price": "asc"
    }
  ],
  "track_total_hits": true
}

POST /my_index/_search
{
  "size": 1000,
  "query": {
    "match": {
      "title": "酒店"
    }
  },
  "sort": [
    {
      "price": "asc"
    }
  ],
  "search_after": [337]
}

@Slf4j
@Service
public class ElasticSearchImpl {
    @Autowired
    private RestHighLevelClient restHighLevelClient;

    public void searchUser() throws IOException {
        SearchSourceBuilder searchSourceBuilder = new SearchSourceBuilder();
        // query 查詢
        MatchQueryBuilder matchQueryBuilder = new MatchQueryBuilder("title","酒店");
        searchSourceBuilder.query(matchQueryBuilder);

        // 計(jì)算總命中數(shù)：track_total_hits
        searchSourceBuilder.trackTotalHits(true);

        // 每次返回3條數(shù)據(jù)
        searchSourceBuilder.size(3);

        // 設(shè)置排序字段
        searchSourceBuilder.sort(SortBuilders.fieldSort("price").order(SortOrder.ASC));

        SearchRequest searchRequest = new SearchRequest(new String[]{"my_index"},searchSourceBuilder);
        SearchResponse searchResponse = restHighLevelClient.search(searchRequest, RequestOptions.DEFAULT);

        List<Map<String, Object>> result = new ArrayList<>();
        while (searchResponse.getHits().getHits()!=null && searchResponse.getHits().getHits().length>0){
            SearchHit[] hits = searchResponse.getHits().getHits();
            for (SearchHit hit : hits) {
                Map<String, Object> sourceAsMap = hit.getSourceAsMap();
                result.add(sourceAsMap);
            }
            // 取得最后一條數(shù)據(jù)的排序值sort，下次查詢時(shí)將從這個(gè)地方開始取數(shù)
            Object[] lastNum = hits[hits.length - 1].getSortValues();
            searchSourceBuilder.searchAfter(lastNum);
            searchRequest.source(searchSourceBuilder);
            // 做下次查詢
            searchResponse = restHighLevelClient.search(searchRequest, RequestOptions.DEFAULT);
        }
        System.out.println(result);
    }
}

16. SpringBoo整合ES實(shí)現(xiàn)：scroll 分頁(yè)查詢?

@Slf4j
@Service
public class ElasticSearchImpl {

    @Autowired
    private RestHighLevelClient restHighLevelClient;

    public void search() throws IOException {
        SearchSourceBuilder searchSourceBuilder = new SearchSourceBuilder();
        // query 查詢
        MatchQueryBuilder matchQueryBuilder = new MatchQueryBuilder("title","酒店");
        searchSourceBuilder.query(matchQueryBuilder);
        // 計(jì)算總命中數(shù)：track_total_hits
        searchSourceBuilder.trackTotalHits(true);
        // 每次返回7條數(shù)據(jù)
        searchSourceBuilder.size(7);
        // 設(shè)置排序字段
        searchSourceBuilder.sort(SortBuilders.fieldSort("price").order(SortOrder.ASC));

        SearchRequest searchRequest = new SearchRequest(new String[]{"my_index"},searchSourceBuilder);
        // 指定游標(biāo)的過(guò)期時(shí)間
        searchRequest.scroll(TimeValue.timeValueMinutes(1L));
        SearchResponse searchResponse = restHighLevelClient.search(searchRequest, RequestOptions.DEFAULT);
        // 獲取 scrollId
        String scrollId = searchResponse.getScrollId();
        SearchHit[] searchHits = searchResponse.getHits().getHits();
        List<Map<String, Object>> result = new ArrayList<>();
        for (SearchHit hit: searchHits) {
            result.add(hit.getSourceAsMap());
        }
        while (true) {
            // 根據(jù) scrollId 查詢下一頁(yè)數(shù)據(jù)
            SearchScrollRequest scrollRequest = new SearchScrollRequest(scrollId);
            // 指定游標(biāo)的過(guò)期時(shí)間
            scrollRequest.scroll(TimeValue.timeValueMinutes(1L));
            SearchResponse scrollResp = restHighLevelClient.scroll(scrollRequest, RequestOptions.DEFAULT);
            SearchHit[] hits = scrollResp.getHits().getHits();
            if (hits != null && hits.length > 0) {
                for (SearchHit hit : hits) {
                    result.add(hit.getSourceAsMap());
                }
            } else {
                break;
            }
        }
        System.out.println(result);
        // After checking, we delete the id stored in the cache. After scrolling, clear the scrolling context
        ClearScrollRequest clearScrollRequest = new ClearScrollRequest();
        clearScrollRequest.addScrollId(scrollId);
        ClearScrollResponse clearScrollResponse = restHighLevelClient.clearScroll(clearScrollRequest, RequestOptions.DEFAULT);
        boolean succeeded = clearScrollResponse.isSucceeded();
        System.out.println(succeeded);
        restHighLevelClient.close();
    }
}

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