Run a knn search | Elasticsearch API documentation (v8)

Run a knn search Deprecated Technical preview

POST /{index}/_knn_search

NOTE: The kNN search API has been replaced by the knn option in the search API.

Perform a k-nearest neighbor (kNN) search on a dense_vector field and return the matching documents. Given a query vector, the API finds the k closest vectors and returns those documents as search hits.

Elasticsearch uses the HNSW algorithm to support efficient kNN search. Like most kNN algorithms, HNSW is an approximate method that sacrifices result accuracy for improved search speed. This means the results returned are not always the true k closest neighbors.

The kNN search API supports restricting the search using a filter. The search will return the top k documents that also match the filter query.

A kNN search response has the exact same structure as a search API response. However, certain sections have a meaning specific to kNN search:

The document _score is determined by the similarity between the query and document vector.
The hits.total object contains the total number of nearest neighbor candidates considered, which is num_candidates * num_shards. The hits.total.relation will always be eq, indicating an exact value.

Path parameters

index string | array[string] Required

A comma-separated list of index names to search; use _all or to perform the operation on all indices.

Query parameters

routing string

A comma-separated list of specific routing values.

application/json

Body

_source boolean | object

Defines how to fetch a source. Fetching can be disabled entirely, or the source can be filtered.
One of:
_types:SourceConfig boolean _types:SourceFilter object
Hide attributes Show attributes

excludes string | array[string]

includes string | array[string]
docvalue_fields array[object]

The request returns doc values for field names matching these patterns in the hits.fields property of the response. It accepts wildcard (*) patterns.
Hide docvalue_fields attributes Show docvalue_fields attributes object
- field string Required
  
  Path to field or array of paths. Some API's support wildcards in the path to select multiple fields.
- format string
  
  The format in which the values are returned.
- include_unmapped boolean
stored_fields string | array[string]
fields string | array[string]
filter object | array[object]

A query to filter the documents that can match. The kNN search will return the top k documents that also match this filter. The value can be a single query or a list of queries. If filter isn't provided, all documents are allowed to match.

One of:
query_dsl:QueryContainer object array-2 array[object]

An Elasticsearch Query DSL (Domain Specific Language) object that defines a query.

External documentation

An Elasticsearch Query DSL (Domain Specific Language) object that defines a query.

An Elasticsearch Query DSL (Domain Specific Language) object that defines a query.

External documentation
knn object Required
Hide knn attributes Show knn attributes object
- field string Required
  
  Path to field or array of paths. Some API's support wildcards in the path to select multiple fields.
- query_vector array[number] Required
- k number Required
  
  The final number of nearest neighbors to return as top hits
- num_candidates number Required
  
  The number of nearest neighbor candidates to consider per shard

Responses

200 application/json
Hide response attributes Show response attributes object
- took number Required
  
  The milliseconds it took Elasticsearch to run the request.
- timed_out boolean Required
  
  If true, the request timed out before completion; returned results may be partial or empty.
- _shards object Required
  
  Hide _shards attributes Show _shards attributes object
  
  failed number Required
  
  successful number Required
  
  total number Required
  
  failures array[object]
  
  Hide failures attributes Show failures attributes object
  
  index string
  
  node string
  
  reason object Required
  
  Hide reason attributes Show reason attributes object
  
  type string Required
  
  The type of error
  
  reason string
  
  A human-readable explanation of the error, in English.
  
  stack_trace string
  
  The server stack trace. Present only if the error_trace=true parameter was sent with the request.
  
  caused_by object
  
  root_cause array[object]
  
  suppressed array[object]
  
  shard number Required
  
  status string
  
  skipped number
- hits object Required
  
  Hide hits attributes Show hits attributes object
  
  total object | number
  
  Total hit count information, present only if track_total_hits wasn't false in the search request.
  
  One of:
  _types:TotalHits object number-2 number
  
  hits array[object] Required
  
  Hide hits attributes Show hits attributes object
  
  _index string Required
  
  _id string
  
  _score number | string | null
  
  One of:
  number-1 number string-2 string | null
  
  _explanation object
  
  Hide _explanation attributes Show _explanation attributes object
  
  description string Required
  
  details array[object] Required
  
  value number Required
  
  fields object
  
  Hide fields attribute Show fields attribute object
  
  * object Additional properties
  
  highlight object
  
  Hide highlight attribute Show highlight attribute object
  
  * array[string] Additional properties
  
  inner_hits object
  
  Hide inner_hits attribute Show inner_hits attribute object
  
  * object Additional properties
  
  Hide * attribute Show * attribute object
  
  hits object Required
  
  matched_queries array[string] | object
  
  One of:
  array-1 array[string] object-2 object
  
  _nested object
  
  Hide _nested attributes Show _nested attributes object
  
  field string Required
  
  Path to field or array of paths. Some API's support wildcards in the path to select multiple fields.
  
  offset number Required
  
  _nested object
  
  _ignored array[string]
  
  ignored_field_values object
  
  Hide ignored_field_values attribute Show ignored_field_values attribute object
  
  * array[number | string | boolean | null | object] Additional properties
  
  A field value.
  
  _shard string
  
  _node string
  
  _routing string
  
  _source object
  
  _rank number
  
  _seq_no number
  
  _primary_term number
  
  _version number
  
  sort array[number | string | boolean | null | object]
  
  A field value.
  
  A field value.
  
  One of:
  _types:FieldValue number _types:FieldValue number _types:FieldValue string _types:FieldValue boolean _types:FieldValue string | null _types:FieldValue object
  
  max_score number | string | null
  
  One of:
  number-1 number string-2 string | null
- fields object
  
  The field values for the documents. These fields must be specified in the request using the fields parameter.
  
  Hide fields attribute Show fields attribute object
  
  * object Additional properties
- max_score number
  
  The highest returned document score. This value is null for requests that do not sort by score.

POST /{index}/_knn_search

curl \
 --request POST http://api.example.com/{index}/_knn_search \
 --header "Authorization: $API_KEY" \
 --header "Content-Type: application/json" \
 --data '{"":true,"docvalue_fields":[{"field":"string","format":"string","include_unmapped":true}],"stored_fields":"string","fields":"string","filter":{},"knn":{"field":"string","query_vector":[42.0],"k":42.0,"num_candidates":42.0}}'

Request examples

{
  "": true,
  "docvalue_fields": [
    {
      "field": "string",
      "format": "string",
      "include_unmapped": true
    }
  ],
  "stored_fields": "string",
  "fields": "string",
  "filter": {},
  "knn": {
    "field": "string",
    "query_vector": [
      42.0
    ],
    "k": 42.0,
    "num_candidates": 42.0
  }
}

Response examples (200)

{
  "took": 42.0,
  "timed_out": true,
  "_shards": {
    "failed": 42.0,
    "successful": 42.0,
    "total": 42.0,
    "failures": [
      {
        "index": "string",
        "node": "string",
        "reason": {
          "type": "string",
          "reason": "string",
          "stack_trace": "string",
          "caused_by": {},
          "root_cause": [
            {}
          ],
          "suppressed": [
            {}
          ]
        },
        "shard": 42.0,
        "status": "string"
      }
    ],
    "skipped": 42.0
  },
  "hits": {
    "total": {
      "relation": "eq",
      "value": 42.0
    },
    "hits": [
      {
        "_index": "string",
        "_id": "string",
        "_score": 42.0,
        "_explanation": {
          "description": "string",
          "details": [
            {}
          ],
          "value": 42.0
        },
        "fields": {
          "additionalProperty1": {},
          "additionalProperty2": {}
        },
        "highlight": {
          "additionalProperty1": [
            "string"
          ],
          "additionalProperty2": [
            "string"
          ]
        },
        "inner_hits": {
          "additionalProperty1": {
            "hits": {}
          },
          "additionalProperty2": {
            "hits": {}
          }
        },
        "matched_queries": [
          "string"
        ],
        "_nested": {
          "field": "string",
          "offset": 42.0,
          "_nested": {}
        },
        "_ignored": [
          "string"
        ],
        "ignored_field_values": {
          "additionalProperty1": [
            {}
          ],
          "additionalProperty2": [
            {}
          ]
        },
        "_shard": "string",
        "_node": "string",
        "_routing": "string",
        "_source": {},
        "_rank": 42.0,
        "_seq_no": 42.0,
        "_primary_term": 42.0,
        "_version": 42.0,
        "sort": [
          42.0
        ]
      }
    ],
    "max_score": 42.0
  },
  "fields": {
    "additionalProperty1": {},
    "additionalProperty2": {}
  },
  "max_score": 42.0
}

Run a knn search Deprecated Technical preview

Path parameters

Query parameters

Body

_source boolean | object

filter object | array[object]

Responses

total object | number

_score number | string | null

matched_queries array[string] | object

max_score number | string | null