333 lines
9.5 KiB
Plaintext
333 lines
9.5 KiB
Plaintext
[[search-suggesters-completion]]
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=== Completion Suggester
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NOTE: In order to understand the format of suggestions, please
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read the <<search-suggesters>> page first.
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The `completion` suggester provides auto-complete/search-as-you-type
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functionality. This is a navigational feature to guide users to
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relevant results as they are typing, improving search precision.
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It is not meant for spell correction or did-you-mean functionality
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like the `term` or `phrase` suggesters.
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Ideally, auto-complete functionality should be as fast as a user
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types to provide instant feedback relevant to what a user has already
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typed in. Hence, `completion` suggester is optimized for speed.
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The suggester uses data structures that enable fast lookups,
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but are costly to build and are stored in-memory.
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[[completion-suggester-mapping]]
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==== Mapping
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To use this feature, specify a special mapping for this field,
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which indexes the field values for fast completions.
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[source,js]
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--------------------------------------------------
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PUT music/song/_mapping
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{
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"song" : {
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"properties" : {
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...
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"suggest" : {
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"type" : "completion"
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}
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}
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}
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}
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--------------------------------------------------
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Mapping supports the following parameters:
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`analyzer`::
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The index analyzer to use, defaults to `simple`.
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In case you are wondering why we did not opt for the `standard`
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analyzer: We try to have easy to understand behaviour here, and if you
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index the field content `At the Drive-in`, you will not get any
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suggestions for `a`, nor for `d` (the first non stopword).
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`search_analyzer`::
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The search analyzer to use, defaults to value of `analyzer`.
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`preserve_separators`::
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Preserves the separators, defaults to `true`.
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If disabled, you could find a field starting with `Foo Fighters`, if you
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suggest for `foof`.
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`preserve_position_increments`::
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Enables position increments, defaults to `true`.
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If disabled and using stopwords analyzer, you could get a
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field starting with `The Beatles`, if you suggest for `b`. *Note*: You
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could also achieve this by indexing two inputs, `Beatles` and
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`The Beatles`, no need to change a simple analyzer, if you are able to
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enrich your data.
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`max_input_length`::
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Limits the length of a single input, defaults to `50` UTF-16 code points.
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This limit is only used at index time to reduce the total number of
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characters per input string in order to prevent massive inputs from
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bloating the underlying datastructure. Most usecases won't be influenced
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by the default value since prefix completions seldom grow beyond prefixes longer
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than a handful of characters.
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[[indexing]]
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==== Indexing
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You index suggestions like any other field. A suggestion is made of an
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`input` and an optional `weight` attribute. An `input` is the expected
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text to be matched by a suggestion query and the `weight` determines how
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the suggestions will be scored. Indexing a suggestion is as follows:
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[source,js]
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--------------------------------------------------
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PUT music/song/1?refresh=true
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{
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"suggest" : {
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"input": [ "Nevermind", "Nirvana" ],
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"weight" : 34
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}
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}
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--------------------------------------------------
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The following parameters are supported:
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`input`::
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The input to store, this can be an array of strings or just
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a string. This field is mandatory.
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`weight`::
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A positive integer or a string containing a positive integer,
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which defines a weight and allows you to rank your suggestions.
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This field is optional.
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You can index multiple suggestions for a document as follows:
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[source,js]
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--------------------------------------------------
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PUT music/song/1?refresh=true
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{
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"suggest" : [
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{
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"input": "Nevermind",
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"weight" : 10
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},
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{
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"input": "Nirvana",
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"weight" : 3
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}
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]
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}
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--------------------------------------------------
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You can use the following shorthand form. Note that you can not specify
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a weight with suggestion(s).
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[source,js]
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--------------------------------------------------
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{
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"suggest" : [ "Nevermind", "Nirvana" ]
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}
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--------------------------------------------------
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[[querying]]
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==== Querying
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Suggesting works as usual, except that you have to specify the suggest
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type as `completion`. Suggestions are near real-time, which means
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new suggestions can be made visible by <<indices-refresh,refresh>> and
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documents once deleted are never shown.
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[source,js]
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--------------------------------------------------
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POST music/_suggest?pretty
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{
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"song-suggest" : {
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"prefix" : "n",
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"completion" : {
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"field" : "suggest"
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}
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}
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}
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{
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"_shards" : {
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"total" : 5,
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"successful" : 5,
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"failed" : 0
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},
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"song-suggest" : [ {
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"text" : "n",
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"offset" : 0,
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"length" : 1,
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"options" : [ {
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"text" : "Nirvana",
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"score" : 34.0
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} ]
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} ]
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}
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--------------------------------------------------
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The configured weight for a suggestion is returned as `score`.
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The `text` field uses the `input` of your indexed suggestion.
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Suggestions are document oriented, you can specify fields to be
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returned as part of suggestion payload. All field types (`string`,
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`numeric`, `date`, etc) are supported.
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For example, if you index a "title" field along with the suggestion
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as follows:
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[source,js]
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--------------------------------------------------
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POST music/song
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{
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"suggest" : "Nirvana",
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"title" : "Nevermind"
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}
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--------------------------------------------------
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You can get the "title" as part of the suggestion
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payload by specifying it as a `payload`:
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[source,js]
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--------------------------------------------------
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POST music/_suggest?pretty
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{
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"song-suggest" : {
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"prefix" : "n",
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"completion" : {
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"field" : "suggest"
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"payload" : [ "title" ] <1>
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}
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}
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}
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{
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"_shards" : {
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"total" : 5,
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"successful" : 5,
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"failed" : 0
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},
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"song-suggest" : [ {
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"text" : "n",
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"offset" : 0,
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"length" : 1,
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"options" : [ {
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"text" : "Nirvana",
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"score" : 34.0,
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"payload" : {
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"title" : [ "Nevermind" ]
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}
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} ]
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} ]
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}
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--------------------------------------------------
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<1> The fields to be returned as part of each suggestion payload.
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The basic completion suggester query supports the following parameters:
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`field`:: The name of the field on which to run the query (required).
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`size`:: The number of suggestions to return (defaults to `5`).
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`payload`:: The name of the field or field name array to be returned
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as payload (defaults to no fields).
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NOTE: The completion suggester considers all documents in the index.
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See <<suggester-context>> for an explanation of how to query a subset of
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documents instead.
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NOTE: Specifying `payload` fields will incur additional search performance
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hit. The `payload` fields are retrieved eagerly (single pass) for top
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suggestions at the shard level using field data or from doc values.
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[[fuzzy]]
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==== Fuzzy queries
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The completion suggester also supports fuzzy queries - this means,
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you can have a typo in your search and still get results back.
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[source,js]
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--------------------------------------------------
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POST music/_suggest?pretty
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{
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"song-suggest" : {
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"prefix" : "n",
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"completion" : {
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"field" : "suggest",
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"fuzzy" : {
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"fuzziness" : 2
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}
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}
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}
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}
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--------------------------------------------------
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Suggestions that share the longest prefix to the query `prefix` will
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be scored higher.
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The fuzzy query can take specific fuzzy parameters.
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The following parameters are supported:
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[horizontal]
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`fuzziness`::
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The fuzziness factor, defaults to `AUTO`.
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See <<fuzziness>> for allowed settings.
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`transpositions`::
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if set to `true`, transpositions are counted
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as one change instead of two, defaults to `true`
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`min_length`::
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Minimum length of the input before fuzzy
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suggestions are returned, defaults `3`
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`prefix_length`::
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Minimum length of the input, which is not
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checked for fuzzy alternatives, defaults to `1`
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`unicode_aware`::
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If `true`, all measurements (like fuzzy edit
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distance, transpositions, and lengths) are
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measured in Unicode code points instead of
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in bytes. This is slightly slower than raw
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bytes, so it is set to `false` by default.
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NOTE: If you want to stick with the default values, but
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still use fuzzy, you can either use `fuzzy: {}`
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or `fuzzy: true`.
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[[regex]]
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==== Regex queries
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The completion suggester also supports regex queries meaning
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you can express a prefix as a regular expression
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[source,js]
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--------------------------------------------------
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POST music/_suggest?pretty
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{
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"song-suggest" : {
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"regex" : "n[ever|i]r",
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"completion" : {
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"field" : "suggest",
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}
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}
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}
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--------------------------------------------------
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The regex query can take specific regex parameters.
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The following parameters are supported:
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[horizontal]
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`flags`::
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Possible flags are `ALL` (default), `ANYSTRING`, `COMPLEMENT`,
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`EMPTY`, `INTERSECTION`, `INTERVAL`, or `NONE`. See <<query-dsl-regexp-query, regexp-syntax>>
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for their meaning
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`max_determinized_states`::
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Regular expressions are dangerous because it's easy to accidentally
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create an innocuous looking one that requires an exponential number of
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internal determinized automaton states (and corresponding RAM and CPU)
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for Lucene to execute. Lucene prevents these using the
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`max_determinized_states` setting (defaults to 10000). You can raise
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this limit to allow more complex regular expressions to execute.
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