When to use docvalue_fields

Elastic Stack Elasticsearch
1

Hi,

I see that Kibana is using docvalue_fields all the time for the @timestamp field.

When is using docvalue_fields vs stored_fields better? Is there a general use case? Aren't all fields fetched using doc_values anyway?

2

I'm not sure they are supposed to be interchangeable.

Fields | Elasticsearch Reference [5.6] | Elastic states;

The stored_fields parameter is about fields that are explicitly marked as stored in the mapping, which is off by default and generally not recommended.

3

And what about docvalue_fields?

4

Can you elaborate?

5

Sure.

There is this docvalue_fields option for the Search API: https://www.elastic.co/guide/en/elasticsearch/reference/5.6/search-request-docvalue-fields.html

When should I use that?
My index has only keyword fields and all have doc_values enabled for them, so what does this option do in the Search API?

6

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7

Kibana uses docvalue_fields for date fields to get the value back in a consistent format. If Kibana used the value from _source, then parsing the date would be almost impossible because the formats would vary wildly from installation to installation.