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94 lines
3.2 KiB
Text
94 lines
3.2 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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The `doc_values` field is an on-disk data structure that is built at index time and
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enables efficient data access. It stores the same values as
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`_source`, but in a column-oriented format that is more efficient for
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sorting and aggregations.
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Doc values are supported on most field types,
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excluding `text` and `annotated_text` fields. See also <<doc-values-disable>>.
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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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[[doc-values-disable]]
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==== Disabling doc values
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For all fields that support them, `doc_values` are enabled by default. In
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some field types, such as <<search-as-you-type,`search_as_you_type`>>,
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`doc_values` appear in API responses but can't be configured. Setting
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`doc_values` for these fields might result in an error or have no effect.
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If you're
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certain you don't need to sort or aggregate on a field or access its
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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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