elasticsearch中bucket_script聚合父级必须是多桶聚合

亦凉 2021-11-10 13:56 591阅读 0赞

## 场景 ##

业务需求中，在计算人均通话数时，使用聚合的时候使用到了内联以及反内联聚合，当`bucket_script`聚合作为反内联`reverse_nested`的子聚和的时候，会报如下错误：

org.elasticsearch.ElasticsearchException: Elasticsearch exception [type=class_cast_exception, reason=org.elasticsearch.search.aggregations.bucket.nested.InternalReverseNested cannot be cast to org.elasticsearch.search.aggregations.InternalMultiBucketAggregation]

该场景中的嵌套聚合中的子聚合如下（父级聚合此处不展示）：

{ 
    	"reverse_nested": { 
    		"reverse_nested": { },
    		"aggregations": { 
    			"agg_count": { 
    				"value_count": { 
    					"field": "taskId.keyword"
    				}
    			},
    			"agg_cardinality_tel": { 
    				"cardinality": { 
    					"field": "tel.keyword"
    				}
    			},
    			"agg_bucketScript": { 
    				"bucket_script": { 
    					"buckets_path": { 
    						"userCount": "agg_cardinality_tel",
    						"docCount": "agg_count"
    					},
    					"script": { 
    						"source": "params.docCount / params.userCount",
    						"lang": "painless"
    					},
    					"gap_policy": "skip"
    				}
    			}
    		}
    	}
    }

## 原因分析 ##

`bucket_script`聚合的是建立在多桶聚合的前提下，即父级聚合必须是多桶聚合，[官方文档][Link 1]已对此做过说明。

> `bucket_selector` 等聚合方式的聚合场景亦是如此。

A parent pipeline aggregation which executes a script which can perform per bucket computations on specified metrics in the parent multi-bucket aggregation. The specified metric must be numeric and the script must return a numeric value.

## 解决方案 ##

将`bucket_script`聚合与`reverse_nested`聚合放在同层级，关联path即可。

{ 
    	"reverse_nested": { 
    		"reverse_nested": { },
    		"aggregations": { 
    			"agg_count": { 
    				"value_count": { 
    					"field": "taskId.keyword"
    				}
    			},
    			"agg_cardinality_tel": { 
    				"cardinality": { 
    					"field": "tel.keyword"
    				}
    			}
    		}
    	},
    	"agg_bucketScript": { 
    		"bucket_script": { 
    			"buckets_path": { 
    				"userCount": "reverse_nested>agg_cardinality_tel",
    				"docCount": "reverse_nested>agg_count"
    			},
    			"script": { 
    				"source": "params.docCount / params.userCount",
    				"lang": "painless"
    			},
    			"gap_policy": "skip"
    		}
    	}
    }

[Link 1]: https://www.elastic.co/guide/en/elasticsearch/reference/6.4/search-aggregations-pipeline-bucket-script-aggregation.html#search-aggregations-pipeline-bucket-script-aggregation