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Explain API

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Explain API

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The explain api computes a score explanation for a query and a specific document. This can give useful feedback whether a document matches or didn’t match a specific query.

Note that a single index must be provided to the index parameter.

Usage

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Full query example:

GET /twitter/_explain/0
{
      "query" : {
        "match" : { "message" : "elasticsearch" }
      }
}

This will yield the following result:

{
   "_index":"twitter",
   "_type":"_doc",
   "_id":"0",
   "matched":true,
   "explanation":{
      "value":1.6943597,
      "description":"weight(message:elasticsearch in 0) [PerFieldSimilarity], result of:",
      "details":[
         {
            "value":1.6943597,
            "description":"score(freq=1.0), product of:",
            "details":[
               {
                  "value":2.2,
                  "description":"boost",
                  "details":[]
               },
               {
                  "value":1.3862944,
                  "description":"idf, computed as log(1 + (N - n + 0.5) / (n + 0.5)) from:",
                  "details":[
                     {
                        "value":1,
                        "description":"n, number of documents containing term",
                        "details":[]
                     },
                     {
                        "value":5,
                        "description":"N, total number of documents with field",
                        "details":[]
                     }
                  ]
               },
               {
                  "value":0.5555555,
                  "description":"tf, computed as freq / (freq + k1 * (1 - b + b * dl / avgdl)) from:",
                  "details":[
                     {
                        "value":1.0,
                        "description":"freq, occurrences of term within document",
                        "details":[]
                     },
                     {
                        "value":1.2,
                        "description":"k1, term saturation parameter",
                        "details":[]
                     },
                     {
                        "value":0.75,
                        "description":"b, length normalization parameter",
                        "details":[]
                     },
                     {
                        "value":3.0,
                        "description":"dl, length of field",
                        "details":[]
                     },
                     {
                        "value":5.4,
                        "description":"avgdl, average length of field",
                        "details":[]
                     }
                  ]
               }
            ]
         }
      ]
   }
}

There is also a simpler way of specifying the query via the q parameter. The specified q parameter value is then parsed as if the query_string query was used. Example usage of the q parameter in the explain api:

GET /twitter/_explain/0?q=message:search

This will yield the same result as the previous request.

All parameters:

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`_source`	Set to `true` to retrieve the `_source` of the document explained. You can also retrieve part of the document by using `_source_includes` & `_source_excludes` (see Get API for more details)
`stored_fields`	Allows to control which stored fields to return as part of the document explained.
`routing`	Controls the routing in the case the routing was used during indexing.
`parent`	Same effect as setting the routing parameter.
`preference`	Controls on which shard the explain is executed.
`source`	Allows the data of the request to be put in the query string of the url.
`q`	The query string (maps to the query_string query).
`df`	The default field to use when no field prefix is defined within the query.
`analyzer`	The analyzer name to be used when analyzing the query string. Defaults to the default search analyzer.
`analyze_wildcard`	Should wildcard and prefix queries be analyzed or not. Defaults to false.
`lenient`	If set to true will cause format based failures (like providing text to a numeric field) to be ignored. Defaults to false.
`default_operator`	The default operator to be used, can be AND or OR. Defaults to OR.

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