String datatype

Fields of type string accept text values. Strings may be sub-divided into:

Full text

Full text values, like the body of an email, are typically used for text based relevance searches, such as: Find the most relevant documents that match a query for "quick brown fox".

These fields are analyzed, that is they are passed through an analyzer to convert the string into a list of individual terms before being indexed. The analysis process allows Elasticsearch to search for individual words within each full text field. Full text fields are not used for sorting and seldom used for aggregations (although the significant terms aggregation is a notable exception).

Keywords
Keywords are exact values like email addresses, hostnames, status codes, or tags. They are typically used for filtering (Find me all blog posts where status is published), for sorting, and for aggregations. Keyword fields are not_analyzed. Instead, the exact string value is added to the index as a single term.

Below is an example of a mapping for a full text (analyzed) and a keyword (not_analyzed) string field:

PUT my_index
{
  "mappings": {
    "my_type": {
      "properties": {
        "full_name": { 
          "type":  "string"
        },
        "status": {
          "type":  "string", 
          "index": "not_analyzed"
        }
      }
    }
  }
}

The full_name field is an analyzed full text field — index:analyzed is the default.

The status field is a not_analyzed keyword field.

Sometimes it is useful to have both a full text (analyzed) and a keyword (not_analyzed) version of the same field: one for full text search and the other for aggregations and sorting. This can be achieved with multi-fields.

Parameters for string fields

The following parameters are accepted by string fields:

analyzer

The analyzer which should be used for analyzed string fields, both at index-time and at search-time (unless overridden by the search_analyzer). Defaults to the default index analyzer, or the standard analyzer.

boost

Field-level index time boosting. Accepts a floating point number, defaults to 1.0.

doc_values

Should the field be stored on disk in a column-stride fashion, so that it can later be used for sorting, aggregations, or scripting? Accepts true or false. Defaults to true for not_analyzed fields. Analyzed fields do not support doc values.

fielddata

Can the field use in-memory fielddata for sorting, aggregations, or scripting? Accepts { "format": "disabled" } or { "format": "paged_bytes" } (default). Not analyzed fields will use doc values in preference to fielddata.

fields

Multi-fields allow the same string value to be indexed in multiple ways for different purposes, such as one field for search and a multi-field for sorting and aggregations, or the same string value analyzed by different analyzers.

ignore_above

Do not index or analyze any string longer than this value. Defaults to 0 (disabled).

include_in_all

Whether or not the field value should be included in the _all field? Accepts true or false. Defaults to false if index is set to no, or if a parent object field sets include_in_all to false. Otherwise defaults to true.

index

Should the field be searchable? Accepts analyzed (default, treat as full-text field), not_analyzed (treat as keyword field) and no.

index_options

What information should be stored in the index, for search and highlighting purposes. Defaults to positions for analyzed fields, and to docs for not_analyzed fields.

norms

Whether field-length should be taken into account when scoring queries. Defaults depend on the index setting:

  • analyzed fields default to { "enabled": true, "loading": "lazy" }.
  • not_analyzed fields default to { "enabled": false }.

null_value

Accepts a string value which is substituted for any explicit null values. Defaults to null, which means the field is treated as missing. If the field is analyzed, the null_value will also be analyzed.

position_increment_gap

The number of fake term position which should be inserted between each element of an array of strings. Defaults to the position_increment_gap configured on the analyzer which defaults to 100. 100 was chosen because it prevents phrase queries with reasonably large slops (less than 100) from matching terms across field values.

store

Whether the field value should be stored and retrievable separately from the _source field. Accepts true or false (default).

search_analyzer

The analyzer that should be used at search time on analyzed fields. Defaults to the analyzer setting.

search_quote_analyzer

The analyzer that should be used at search time when a phrase is encountered. Defaults to the search_analyzer setting.

similarity

Which scoring algorithm or similarity should be used. Defaults to default, which uses TF/IDF.

term_vector

Whether term vectors should be stored for an analyzed field. Defaults to no.