index_prefixes

The index_prefixes parameter enables the indexing of term prefixes to speed up prefix searches. It accepts the following optional settings:

min_chars

The minimum prefix length to index. Must be greater than 0, and defaults to 2. The value is inclusive.

max_chars

The maximum prefix length to index. Must be less than 20, and defaults to 5. The value is inclusive.

This example creates a text field using the default prefix length settings:

 PUT my-index-000001 {
  "mappings": {
    "properties": {
      "body_text": {
        "type": "text",
        "index_prefixes": { }    1
      }
    }
  }
}

1. An empty settings object will use the default min_chars and max_chars settings

This example uses custom prefix length settings:

 PUT my-index-000001 {
  "mappings": {
    "properties": {
      "full_name": {
        "type": "text",
        "index_prefixes": {
          "min_chars" : 1,
          "max_chars" : 10
        }
      }
    }
  }
}

index_prefixes parameter instructs Elasticsearch to create a subfield "._index_prefix". This field will be used to do fast prefix queries. When doing highlighting, add "._index_prefix" subfield to the matched_fields parameter to highlight the main field based on the found matches of the prefix field, like in the request below:

 GET my-index-000001/_search {
  "query": {
    "prefix": {
      "full_name": {
        "value": "ki"
      }
    }
  },
  "highlight": {
    "fields": {
      "full_name": {
        "matched_fields": ["full_name._index_prefix"]
      }
    }
  }
}