elasticsearch - difference between a field and the field.keyword

Question

If I add a document with several fields to an Elasticsearch index, when I view it in Kibana, I get each time the same field twice. One of them will be called

some_field

and the other one will be called

some_field.keyword

Where does this behaviour come from and what is the difference between both of them?

PS: one of them is aggregatable (not sure what that means) and the other (without keyword) is not.

Answer 1

Update : A short answer would be that type: text is analyzed, meaning it is broken up into distinct words when stored, and allows for free-text searches on one or more words in the field. The .keyword field takes the same input and keeps as one large string, meaning it can be aggregated on, and you can use wildcard searches on it. Aggregatable means you can use it in aggregations in elasticsearch, which resembles a sql group by if you are familiar with that. In Kibana you would probably use the .keyword field with aggregations to count distinct values etc.

---

Please take a look on this article about text vs. keyword.

Briefly: since Elasticsearch 5.0 string type was replaced by text and keyword types. Since then when you do not specify explicit mapping, for simple document with string:

{
  "some_field": "string value"
}

below dynamic mapping will be created:

{
  "some_field": {
    "type" "text",
    "fields": {
      "keyword": {
        "type": "keyword",
        "ignore_above": 256
      }
    }
  }
}

As a consequence, it will both be possible to perform full-text search on some_field, and keyword search and aggregations using the some_field.keyword field.

I hope this answers your question.