了解 ElasticSearch 上的聚合结果

Question

我正在处理 ElasticSearch 中的特定查询。查询的目标是返回所有具有最新时间戳的唯一结果。 所以只是为了给出背景，在弹性搜索数据库中，每个具有不同时间戳的唯一字段“x”可以有多个条目。我希望 ES 查询返回每个唯一字段 x 的最新时间戳。 所以数据看起来像 ES 数据库中的：

{"x" : "1", "time": 1536574915}
{"x" : "2", "time": 1536574919}
{"x" : "1", "time": 1536574815}
{"x" : "2", "time": 1536574819}
{"x" : "3", "time": 1536574915}
{"x" : "4", "time": 1536574915}

预期输出是

{"x" : "1", "time": 1536574915}
{"x" : "2", "time": 1536574919}
{"x" : "3", "time": 1536574915}
{"x" : "4", "time": 1536574915}

我目前使用的查询是：

{
            "size": 0,
            "query": {
                "bool": {
                    "must": [],
                    "filter": {
                        "range": {
                            "time": {
                                "lte": "2019-11-16", Can give epoch conversion here
                                "format": "date_optional_time"
                                }
                            }
                        }
                    }
                },
            "aggs": {
                "group_by": {
                 "terms": {
                        "field": "x"
                        },
                    "aggs": {
                        "resource": {
                            "terms": {
                                "field": "time",
                                "size": 1,
                                "order": {
                                    "_key": "desc"
                                }

                            },

                            "aggs": {
                                "include_source": {
                                    "top_hits": {
                                        "from": 0,
                                        "size": 1,
                                        "_source": {}
                                    }
                                }
                            }
                        }
                    }
                }
            }
        }

上述查询返回的结果有

[
    {
        "_scroll_id": "DnF1ZXJ5VGhlbkZldGNoAgAAAAAAAAECFmtnNUY4dHFKUXVldXdQMkNSaE1femcAAAAAAAABAxZrZzVGOHRxSlF1ZXV3UDJDUmhNX3pn",
        "took": 227,
        "timed_out": false,
        "_shards": {
            "total": 2,
            "successful": 2,
            "skipped": 0,
            "failed": 0
        },
        "hits": {
            "total": 343533,
            "max_score": 0.0,
            "hits": [
                {
                }
            ]
},
   "aggregations": {
                "group_by": {
                    "doc_count_error_upper_bound": 4,
                    "sum_other_doc_count": 343513,
                    "buckets": [
                  { # here is the actual data.
                  }
           ]
        }
      }
    },
    {
       #another scroll_id. Removed the data as its huge.
   }
]

我的问题是，上述案例中的独特结果在哪里？ 是在 [hits][hits] 之内还是在“聚合”之内？如果在聚合中，对于一百万条记录，聚合只返回 10 个结果。如果我依赖每个滚动列表中的 [hits][hits]，那么结果是重复的。我试图了解，根据上述查询约束，我可以得到正确的唯一条目。还是查询格式不正确或缺少某些参数。 感谢任何帮助。 谢谢。

Answer 1

您的聚合不正确，因为您要检索每个 x 和 time 的热门匹配，而您的目标是检索每个 x 的最新匹配。您需要修改您的查询，如下所示，即您仅按x 聚合，而在您的top_hits 子聚合中，您通过减少time 对文档进行排序，并且只取最后一个。

{
  "size": 0,
  "aggs": {
    "group_by": {
      "terms": {
        "field": "x"
      },
      "aggs": {
        "resource": {
          "top_hits": {
            "from": 0,
            "size": 1,
            "sort": {
              "time": "desc"
            },
            "_source": {}
          }
        }
      }
    }
  }
}

您要查找的文档位于每个存储桶的 resource.hits.hits 部分：

  "aggregations" : {
    "group_by" : {
      "doc_count_error_upper_bound" : 0,
      "sum_other_doc_count" : 0,
      "buckets" : [
        {
          "key" : "1",
          "doc_count" : 2,
          "resource" : {
            "hits" : {
              "total" : 2,
              "max_score" : null,
              "hits" : [
                {
                  "_index" : "times",
                  "_type" : "doc",
                  "_id" : "PZt7G2cBJos57mIu0oy-",
                  "_score" : null,
                  "_source" : {
                    "x" : "1",
                    "time" : 1536574915
                  },
                  "sort" : [
                    1536574915
                  ]
                }
              ]
            }
          }
        },
        {
          "key" : "2",
          "doc_count" : 2,
          "resource" : {
            "hits" : {
              "total" : 2,
              "max_score" : null,
              "hits" : [
                {
                  "_index" : "times",
                  "_type" : "doc",
                  "_id" : "Ppt7G2cBJos57mIu0oy-",
                  "_score" : null,
                  "_source" : {
                    "x" : "2",
                    "time" : 1536574919
                  },
                  "sort" : [
                    1536574919
                  ]
                }
              ]
            }
          }
        },
        {
          "key" : "3",
          "doc_count" : 1,
          "resource" : {
            "hits" : {
              "total" : 1,
              "max_score" : null,
              "hits" : [
                {
                  "_index" : "times",
                  "_type" : "doc",
                  "_id" : "QZt7G2cBJos57mIu0oy-",
                  "_score" : null,
                  "_source" : {
                    "x" : "3",
                    "time" : 1536574915
                  },
                  "sort" : [
                    1536574915
                  ]
                }
              ]
            }
          }
        },
        {
          "key" : "4",
          "doc_count" : 1,
          "resource" : {
            "hits" : {
              "total" : 1,
              "max_score" : null,
              "hits" : [
                {
                  "_index" : "times",
                  "_type" : "doc",
                  "_id" : "Qpt7G2cBJos57mIu0oy-",
                  "_score" : null,
                  "_source" : {
                    "x" : "4",
                    "time" : 1536574915
                  },
                  "sort" : [
                    1536574915
                  ]
                }
              ]
            }
          }
        }
      ]
    }
  }