78 lines
1.9 KiB
Plaintext
78 lines
1.9 KiB
Plaintext
[[mapper-murmur3]]
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=== Mapper Murmur3 Plugin
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The mapper-murmur3 plugin provides the ability to compute hash of field values
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at index-time and store them in the index. This can sometimes be helpful when
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running cardinality aggregations on high-cardinality and large string fields.
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:plugin_name: mapper-murmur3
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include::install_remove.asciidoc[]
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[[mapper-murmur3-usage]]
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==== Using the `murmur3` field
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The `murmur3` is typically used within a multi-field, so that both the original
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value and its hash are stored in the index:
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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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"my_field": {
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"type": "keyword",
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"fields": {
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"hash": {
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"type": "murmur3"
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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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}
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--------------------------
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// CONSOLE
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Such a mapping would allow to refer to `my_field.hash` in order to get hashes
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of the values of the `my_field` field. This is only useful in order to run
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`cardinality` aggregations:
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[source,js]
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--------------------------
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# Example documents
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PUT my_index/my_type/1
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{
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"my_field": "This is a document"
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}
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PUT my_index/my_type/2
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{
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"my_field": "This is another document"
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}
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GET my_index/_search
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{
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"aggs": {
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"my_field_cardinality": {
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"cardinality": {
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"field": "my_field.hash" <1>
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}
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}
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}
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}
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--------------------------
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// CONSOLE
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<1> Counting unique values on the `my_field.hash` field
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Running a `cardinality` aggregation on the `my_field` field directly would
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yield the same result, however using `my_field.hash` instead might result in
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a speed-up if the field has a high-cardinality. On the other hand, it is
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discouraged to use the `murmur3` field on numeric fields and string fields
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that are not almost unique as the use of a `murmur3` field is unlikely to
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bring significant speed-ups, while increasing the amount of disk space required
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to store the index.
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