count_fields_in_index.md

How to get the number of fields in an index

There is no soleley ES internal way to query this. However, there are different approaches to get (approximate or exact) counts with the help of other tools (e.g. jq, or python). Most of this is taken from this SO post and its answers.

Challenges

• Counting the occurrence of type may lead to wrong results for multi-type fields, e.g. text/keyword.
• Counting the occurrence of type may lead to wrong results for fields with the name type or type as part of the name, e.g. content_type.

Examples

Using curl, grep and wc

From this SO anwser.

curl -s -XGET "https://<user>:<pass>@<elastic.url>:<port>/<index_name>/_mapping?pretty | grep '"type"' | wc -l

Pros:

• one-liner from shell
• grep, wc, and curl generally widely available

Cons:

• counting type occurences may count fields twice or even more (see challenges above)

Using curl and jq

Using curl, the ES _field_caps endpoint and jq lets us count the fields. From this SO answer.

curl -s -XGET "https://<user>:<pass>@<elastic.url>:<port>/<index_name>/_field_caps?fields=*" | jq '.fields|length'       

Pros:

• one-liner from shell
• jq and curl generally widely available

Cons:

• counting _fields.length is not enough to know the number of fields, as there can be sub-fields as well?