71 lines
2.3 KiB
Plaintext
71 lines
2.3 KiB
Plaintext
[[mapping-boost-field]]
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=== `_boost`
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deprecated[1.0.0.RC1,See <<function-score-instead-of-boost>>]
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Boosting is the process of enhancing the relevancy of a document or
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field. Field level mapping allows to define an explicit boost level on a
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specific field. The boost field mapping (applied on the
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<<mapping-root-object-type,root object>>) allows
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to define a boost field mapping where *its content will control the
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boost level of the document*. For example, consider the following
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mapping:
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[source,js]
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--------------------------------------------------
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{
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"tweet" : {
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"_boost" : {"name" : "my_boost", "null_value" : 1.0}
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}
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}
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--------------------------------------------------
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The above mapping defines a mapping for a field named `my_boost`. If the
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`my_boost` field exists within the JSON document indexed, its value will
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control the boost level of the document indexed. For example, the
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following JSON document will be indexed with a boost value of `2.2`:
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[source,js]
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--------------------------------------------------
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{
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"my_boost" : 2.2,
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"message" : "This is a tweet!"
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}
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--------------------------------------------------
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[[function-score-instead-of-boost]]
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==== Function score instead of boost
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Support for document boosting via the `_boost` field has been removed
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from Lucene and is deprecated in Elasticsearch as of v1.0.0.RC1. The
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implementation in Lucene resulted in unpredictable result when
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used with multiple fields or multi-value fields.
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Instead, the <<query-dsl-function-score-query>> can be used to achieve
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the desired functionality by boosting each document by the value in
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any field the document:
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[source,js]
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--------------------------------------------------
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{
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"query": {
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"function_score": {
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"query": { <1>
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"match": {
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"title": "your main query"
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}
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},
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"functions": [{
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"field_value_factor": { <2>
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"field": "my_boost_field"
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}
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}],
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"score_mode": "multiply"
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}
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}
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}
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--------------------------------------------------
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<1> The original query, now wrapped in a `function_score` query.
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<2> This function returns the value in `my_boost_field`, which is then
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multiplied by the query `_score` for each document.
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