171 lines
5.4 KiB
Plaintext
171 lines
5.4 KiB
Plaintext
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[[caching-heavy-aggregations]]
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== Caching heavy aggregations
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Frequently used aggregations (e.g. for display on the home page of a website)
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can be cached for faster responses. These cached results are the same results
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that would be returned by an uncached aggregation -- you will never get stale
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results.
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See <<shard-request-cache>> for more details.
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[[returning-only-agg-results]]
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== Returning only aggregation results
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There are many occasions when aggregations are required but search hits are not. For these cases the hits can be ignored by
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setting `size=0`. For example:
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[source,console]
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--------------------------------------------------
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GET /twitter/_search
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{
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"size": 0,
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"aggregations": {
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"my_agg": {
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"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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// TEST[setup:twitter]
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Setting `size` to `0` avoids executing the fetch phase of the search making the request more efficient.
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[[agg-metadata]]
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== Aggregation Metadata
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You can associate a piece of metadata with individual aggregations at request time that will be returned in place
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at response time.
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Consider this example where we want to associate the color blue with our `terms` aggregation.
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[source,console]
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--------------------------------------------------
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GET /twitter/_search
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{
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"size": 0,
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"aggs": {
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"titles": {
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"terms": {
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"field": "title"
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},
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"meta": {
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"color": "blue"
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}
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}
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}
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}
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--------------------------------------------------
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// TEST[setup:twitter]
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Then that piece of metadata will be returned in place for our `titles` terms aggregation
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[source,console-result]
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--------------------------------------------------
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{
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"aggregations": {
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"titles": {
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"meta": {
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"color" : "blue"
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},
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"doc_count_error_upper_bound" : 0,
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"sum_other_doc_count" : 0,
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"buckets": [
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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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// TESTRESPONSE[s/\.\.\./"took": "$body.took", "timed_out": false, "_shards": "$body._shards", "hits": "$body.hits"/]
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[[returning-aggregation-type]]
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== Returning the type of the aggregation
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Sometimes you need to know the exact type of an aggregation in order to parse its results. The `typed_keys` parameter
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can be used to change the aggregation's name in the response so that it will be prefixed by its internal type.
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Considering the following <<search-aggregations-bucket-datehistogram-aggregation,`date_histogram` aggregation>> named
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`tweets_over_time` which has a sub <<search-aggregations-metrics-top-hits-aggregation, 'top_hits` aggregation>> named
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`top_users`:
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[source,console]
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--------------------------------------------------
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GET /twitter/_search?typed_keys
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{
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"aggregations": {
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"tweets_over_time": {
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"date_histogram": {
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"field": "date",
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"calendar_interval": "year"
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},
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"aggregations": {
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"top_users": {
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"top_hits": {
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"size": 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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}
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--------------------------------------------------
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// TEST[setup:twitter]
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In the response, the aggregations names will be changed to respectively `date_histogram#tweets_over_time` and
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`top_hits#top_users`, reflecting the internal types of each aggregation:
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[source,console-result]
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--------------------------------------------------
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{
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"aggregations": {
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"date_histogram#tweets_over_time": { <1>
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"buckets" : [
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{
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"key_as_string" : "2009-01-01T00:00:00.000Z",
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"key" : 1230768000000,
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"doc_count" : 5,
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"top_hits#top_users" : { <2>
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"hits" : {
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"total" : {
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"value": 5,
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"relation": "eq"
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},
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"max_score" : 1.0,
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"hits" : [
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{
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"_index": "twitter",
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"_type": "_doc",
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"_id": "0",
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"_score": 1.0,
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"_source": {
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"date": "2009-11-15T14:12:12",
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"message": "trying out Elasticsearch",
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"user": "kimchy",
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"likes": 0
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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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},
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...
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}
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--------------------------------------------------
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// TESTRESPONSE[s/\.\.\./"took": "$body.took", "timed_out": false, "_shards": "$body._shards", "hits": "$body.hits"/]
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<1> The name `tweets_over_time` now contains the `date_histogram` prefix.
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<2> The name `top_users` now contains the `top_hits` prefix.
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NOTE: For some aggregations, it is possible that the returned type is not the same as the one provided with the
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request. This is the case for Terms, Significant Terms and Percentiles aggregations, where the returned type
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also contains information about the type of the targeted field: `lterms` (for a terms aggregation on a Long field),
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`sigsterms` (for a significant terms aggregation on a String field), `tdigest_percentiles` (for a percentile
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aggregation based on the TDigest algorithm).
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