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86 lines
3 KiB
Text
86 lines
3 KiB
Text
[[doc-values]]
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=== `doc_values`
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Most fields are <<mapping-index,indexed>> by default, which makes them
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searchable. The inverted index allows queries to look up the search term in
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unique sorted list of terms, and from that immediately have access to the list
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of documents that contain the term.
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Sorting, aggregations, and access to field values in scripts requires a
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different data access pattern. Instead of looking up the term and finding
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documents, we need to be able to look up the document and find the terms that
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it has in a field.
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Doc values are the on-disk data structure, built at document index time, which
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makes this data access pattern possible. They store the same values as the
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`_source` but in a column-oriented fashion that is way more efficient for
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sorting and aggregations. Doc values are supported on almost all field types,
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with the __notable exception of `text` and `annotated_text` fields__.
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[[doc-value-only-fields]]
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==== Doc-value-only fields
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<<number,Numeric types>>, <<date,date types>>, the <<boolean,boolean type>>,
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<<ip,ip type>>, <<geo-point,geo_point type>> and the <<keyword,keyword type>>
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can also be queried when they are not <<mapping-index,indexed>> but only
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have doc values enabled.
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Query performance on doc values is much slower than on index structures, but
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offers an interesting tradeoff between disk usage and query performance for
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fields that are only rarely queried and where query performance is not as
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important. This makes doc-value-only fields a good fit for fields that are
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not expected to be normally used for filtering, for example gauges or
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counters on metric data.
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Doc-value-only fields can be configured as follows:
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[source,console]
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--------------------------------------------------
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PUT my-index-000001
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{
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"mappings": {
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"properties": {
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"status_code": { <1>
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"type": "long"
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},
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"session_id": { <2>
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"type": "long",
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"index": false
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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 `status_code` field is a regular long field.
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<2> The `session_id` field has `index` disabled, and is therefore a
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doc-value-only long field as doc values are enabled by default.
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==== Disabling doc values
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All fields which support doc values have them enabled by default. If you are
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sure that you don't need to sort or aggregate on a field, or access the field
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value from a script, you can disable doc values in order to save disk space:
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[source,console]
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--------------------------------------------------
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PUT my-index-000001
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{
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"mappings": {
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"properties": {
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"status_code": { <1>
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"type": "keyword"
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},
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"session_id": { <2>
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"type": "keyword",
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"doc_values": false
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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 `status_code` field has `doc_values` enabled by default.
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<2> The `session_id` has `doc_values` disabled, but can still be queried.
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NOTE: You cannot disable doc values for <<wildcard-field-type,`wildcard`>>
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fields.
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