elasticsearch sort (“Missing Values” 和 “Unmapped Fields” 的区别)

missing value: 

   index中定义了对应字段, 但是对于一些特别的文档不存在该字段的内容, missing value 决定对于这些文档采取的策略

unmapped field:

  当你从多个index中查找并且排序时, 对于一个index存在filed1, 但是另一个index没有定义filed1, 通过unmapped field解决index的mappings中没有定义的情况.

总结: missing value 解决index的mapping中定义了但是doc中缺失该字段, unmapped filed 解决index的mapping上就没有定义对应的sort字段的情况;

主要翻译网上的内容:

It really depends on how many indices you are using. Missing values define how to sort documents from the index where this field is defined but some documents don't have any value specified for this field. The unmapped fields are needed when you search multiple indices and you are sorting on a field that is defined in one index, but not defined in another.

摘自:https://discuss.elastic.co/t/difference-between-missing-values-and-unmapped-fields/132382