60 lines
1.9 KiB
Plaintext
60 lines
1.9 KiB
Plaintext
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[[index-boost]]
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=== `boost`
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Individual fields can be _boosted_ -- count more towards the relevance score
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-- at index time, with the `boost` parameter as follows:
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[source,js]
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--------------------------------------------------
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PUT my_index
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{
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"mappings": {
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"my_type": {
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"properties": {
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"title": {
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"type": "string",
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"boost": 2 <1>
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},
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"content": {
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"type": "string"
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}
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}
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}
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}
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}
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--------------------------------------------------
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// AUTOSENSE
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<1> Matches on the `title` field will have twice the weight as those on the
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`content` field, which has the default `boost` of `1.0`.
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Note that a `title` field will usually be shorter than a `content` field. The
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default relevance calculation takes field length into account, so a short
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`title` field will have a higher natural boost than a long `content` field.
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[WARNING]
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.Why index time boosting is a bad idea
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==================================================
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We advise against using index time boosting for the following reasons:
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* You cannot change index-time `boost` values without reindexing all of your
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documents.
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* Every query supports query-time boosting which achieves the same effect. The
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difference is that you can tweak the `boost` value without having to reindex.
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* Index-time boosts are stored as part of the <<norms,`norm`>>, which is only one
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byte. This reduces the resolution of the field length normalization factor
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which can lead to lower quality relevance calculations.
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==================================================
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The only advantage that index time boosting has is that it is copied with the
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value into the <<mapping-all-field,`_all`>> field. This means that, when
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querying the `_all` field, words that originated from the `title` field will
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have a higher score than words that originated in the `content` field.
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This functionality comes at a cost: queries on the `_all` field are slower
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when index-time boosting is used.
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