Test rate aggregation on counters (#96472)

This is a test showing how rate aggregation result changes when computed on a counter field as opposed to non-metric numeric fields or metric fields of type "gauge". The original rate aggregation implementation (different form the time series rate aggregation) requires it to be nested inside a date histogram or composite aggregation. In the time series implementation we use the actual timestamp difference instead of the date histogram calendar interval.

x-pack/plugin/src/yamlRestTest/resources/rest-api-spec/test/analytics/rate.yml

@@ -205,3 +205,126 @@
   - length: { aggregations.by_date.buckets: 2 }
   - match: { aggregations.by_date.buckets.0.rate.value: 6.0 }
   - match: { aggregations.by_date.buckets.1.rate.value: 18.0 }
+
+---
+"rate aggregation on counter field":
+  - skip:
+      version: " - 8.6.99"
+      reason: "counter field support added in 8.7"
+      features: close_to
+
+  - do:
+      indices.create:
+        index: test-rate
+        body:
+          settings:
+            index:
+              mode: time_series
+              routing_path: [ host ]
+              time_series:
+                start_time: 2021-04-28T00:00:00Z
+                end_time: 2021-04-29T00:00:00Z
+          mappings:
+            properties:
+              "@timestamp":
+                type: date
+              host:
+                type: keyword
+                time_series_dimension: true
+              bytes_gauge:
+                type : long
+                time_series_metric: gauge
+              bytes_counter:
+                type: long
+                time_series_metric: counter
+              byes:
+                type: long
+
+  - do:
+      bulk:
+        refresh: true
+        index: test-rate
+        body:
+          - '{"index": {}}'
+          - '{"@timestamp": "2021-04-28T18:50:00.000Z", "host": "one", "bytes_counter": 1000, "bytes_gauge": 1000, "bytes": 1000 }'
+          - '{"index": {}}'
+          - '{"@timestamp": "2021-04-28T18:50:01.000Z", "host": "one", "bytes_counter": 1100, "bytes_gauge": 100, "bytes": 100 }'
+          - '{"index": {}}'
+          - '{"@timestamp": "2021-04-28T18:50:02.000Z", "host": "one", "bytes_counter": 1200, "bytes_gauge": 100, "bytes": 100 }'
+          - '{"index": {}}'
+          - '{"@timestamp": "2021-04-28T18:50:03.000Z", "host": "one", "bytes_counter": 1250, "bytes_gauge": 50, "bytes": 50 }'
+          - '{"index": {}}'
+          - '{"@timestamp": "2021-04-28T18:50:04.000Z", "host": "one", "bytes_counter": 1310, "bytes_gauge": 60, "bytes": 60 }'
+          - '{"index": {}}'
+          - '{"@timestamp": "2021-04-28T18:50:05.000Z", "host": "one", "bytes_counter": 1350, "bytes_gauge": 40, "bytes": 40 }'
+          - '{"index": {}}'
+          - '{"@timestamp": "2021-04-28T18:50:06.000Z", "host": "one", "bytes_counter": 1420, "bytes_gauge": 70, "bytes": 70 }'
+          - '{"index": {}}'
+          - '{"@timestamp": "2021-04-28T18:50:07.000Z", "host": "one", "bytes_counter": 1500, "bytes_gauge": 80, "bytes": 80 }'
+          - '{"index": {}}'
+          - '{"@timestamp": "2021-04-28T18:50:08.000Z", "host": "one", "bytes_counter": 1520, "bytes_gauge": 20, "bytes": 20 }'
+          - '{"index": {}}'
+          - '{"@timestamp": "2021-04-28T18:50:09.000Z", "host": "one", "bytes_counter": 1550, "bytes_gauge": 30, "bytes": 30 }'
+
+  - do:
+      search:
+        index: test-rate
+        body:
+          size: 0
+          query:
+            bool:
+              filter:
+                range:
+                  "@timestamp":
+                    gte: "2021-04-28T18:00:00.000Z"
+                    lte: "2021-04-28T19:00:00.000Z"
+          aggs:
+            date_histogram:
+              date_histogram:
+                field: "@timestamp"
+                fixed_interval: 1m
+                time_zone: Europe/Ljubljana
+                min_doc_count: 1
+              aggs:
+                8:
+                  sum_bucket:
+                    buckets_path: 8-bucket>8-metric
+                9:
+                  sum_bucket:
+                    buckets_path: 9-bucket>9-metric
+                10:
+                  rate:
+                    field: bytes_gauge
+                    unit: second
+                11:
+                  rate:
+                    field: bytes
+                    unit: second
+                8-bucket:
+                  terms:
+                    field: host
+                    order:
+                      _key: desc
+                    size: 500
+                  aggs:
+                    8-metric:
+                      rate:
+                        field: bytes_gauge
+                        unit: second
+                9-bucket:
+                  time_series: { }
+                  aggs:
+                    9-metric:
+                      rate:
+                        field: bytes_counter
+                        unit: second
+
+  - match: { hits.total.value: 10 }
+  - length: { aggregations.date_histogram.buckets: 1 }
+  - match: { aggregations.date_histogram.buckets.0.key_as_string: "2021-04-28T20:50:00.000+02:00" }
+  - match: { aggregations.date_histogram.buckets.0.doc_count: 10 }
+  - close_to: { aggregations.date_histogram.buckets.0.11.value: { value: 25.83, error: 0.01 } }
+  - close_to: { aggregations.date_histogram.buckets.0.10.value: { value: 25.83, error: 0.01 } }
+  - close_to: { aggregations.date_histogram.buckets.0.8.value: { value: 25.83, error: 0.01 } }
+  # Rate aggregation on counters uses the actual bucket time interval instead of the parent date histogram calendar interval
+  - close_to: { aggregations.date_histogram.buckets.0.9.value: { value: 0.06, error: 0.01 } }