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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.

The index and type parameters expect a single index and a single type respectively.

Usage

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Full query example:

curl -XGET 'localhost:9200/twitter/tweet/1/_explain' -d '{
      "query" : {
        "term" : { "message" : "search" }
      }
}'

This will yield the following result:

{
  "matches" : true,
  "explanation" : {
    "value" : 0.15342641,
    "description" : "fieldWeight(message:search in 0), product of:",
    "details" : [ {
      "value" : 1.0,
      "description" : "tf(termFreq(message:search)=1)"
    }, {
      "value" : 0.30685282,
      "description" : "idf(docFreq=1, maxDocs=1)"
    }, {
      "value" : 0.5,
      "description" : "fieldNorm(field=message, doc=0)"
    } ]
  }
}

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:

curl -XGET 'localhost:9200/twitter/tweet/1/_explain?q=message:search'

This will yield the same result as the previous request.

All parameters:

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`_source`	[1.0.0.Beta1] Added in 1.0.0.Beta1. Set to `true` to retrieve the `_source` of the document explained. You can also retrieve part of the document by using `_source_include` & `_source_exclude` (see Get API for more details)
`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. Defaults to _all field.
`analyzer`	The analyzer name to be used when analyzing the query string. Defaults to the analyzer of the _all field.
`analyze_wildcard`	Should wildcard and prefix queries be analyzed or not. Defaults to false.
`lowercase_expanded_terms`	Should terms be automatically lowercased or not. Defaults to true.
`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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