76 lines
2.3 KiB
Plaintext
76 lines
2.3 KiB
Plaintext
[[search-aggregations-bucket-sampler-aggregation]]
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=== Sampler Aggregation
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experimental[]
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A filtering aggregation used to limit any sub aggregations' processing to a sample of the top-scoring documents.
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.Example use cases:
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* Tightening the focus of analytics to high-relevance matches rather than the potentially very long tail of low-quality matches
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* Reducing the running cost of aggregations that can produce useful results using only samples e.g. `significant_terms`
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Example:
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[source,js]
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--------------------------------------------------
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{
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"query": {
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"match": {
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"text": "iphone"
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}
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},
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"aggs": {
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"sample": {
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"sampler": {
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"shard_size": 200
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},
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"aggs": {
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"keywords": {
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"significant_terms": {
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"field": "text"
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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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Response:
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[source,js]
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--------------------------------------------------
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{
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...
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"aggregations": {
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"sample": {
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"doc_count": 1000,<1>
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"keywords": {
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"doc_count": 1000,
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"buckets": [
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...
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{
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"key": "bend",
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"doc_count": 58,
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"score": 37.982536582524276,
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"bg_count": 103
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},
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....
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}
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--------------------------------------------------
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<1> 1000 documents were sampled in total because we asked for a maximum of 200 from an index with 5 shards. The cost of performing the nested significant_terms aggregation was therefore limited rather than unbounded.
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==== shard_size
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The `shard_size` parameter limits how many top-scoring documents are collected in the sample processed on each shard.
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The default value is 100.
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==== Limitations
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===== Cannot be nested under `breadth_first` aggregations
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Being a quality-based filter the sampler aggregation needs access to the relevance score produced for each document.
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It therefore cannot be nested under a `terms` aggregation which has the `collect_mode` switched from the default `depth_first` mode to `breadth_first` as this discards scores.
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In this situation an error will be thrown. |