[Monitoring] Only do a single date_histogram agg for get_nodes calls (e…

…lastic#43481)

* I think this is working now

* Add a way to uncovert, and then fix tests

* Remove unnecessary export

x-pack/legacy/plugins/monitoring/server/lib/elasticsearch/convert_metric_names.js

@@ -0,0 +1,76 @@
+/*
+ * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+ * or more contributor license agreements. Licensed under the Elastic License;
+ * you may not use this file except in compliance with the Elastic License.
+ */
+
+import { cloneDeep } from 'lodash';
+import { LISTING_METRICS_NAMES } from './nodes/get_nodes/nodes_listing_metrics';
+
+// We should use some explicit prefix for the converted aggregation name
+// so we can easily strip them out later (see `convertMetricNames` and `uncovertMetricNames`)
+const CONVERTED_TOKEN = `odh_`;
+
+/**
+ * This work stemmed from this issue: https://github.com/elastic/kibana/issues/43477
+ *
+ * Historically, the `get_nodes` function created an aggregation with multiple sub `date_histogram`
+ * aggregations for each metric aggregation. From a top down view, the entire aggregations look liked:
+ * `terms` agg -> [`date_histogram` -> metric agg]x6
+ * However, this is very inefficient, as each `date_histogram` will create a new set of search buckets
+ * unnecessarily and users will hit the `search.max_buckets` ceiling sooner.
+ *
+ * To solve this, we need to create a single `date_histogram`, then perform each metric agg as a sub aggregations
+ * of this single `date_histogram`. This is not straightforward though. The logic to build these aggregations
+ * is shared code between the rest of the monitoring code base and is not easily updated to accommodate the
+ * changes from above. To circumvent that, this function will adjust the existing aggregation names to work
+ * for a single date_histogram.
+ *
+ * @param string prefix - This is the aggregation name prefix where the rest of the name will be the type of aggregation
+ * @param object metricObj The metric aggregation itself
+ */
+export function convertMetricNames(prefix, metricObj) {
+  return Object.entries(metricObj).reduce((newObj, [key, value]) => {
+    const newValue = cloneDeep(value);
+    if (key.includes('_deriv') && newValue.derivative) {
+      newValue.derivative.buckets_path = `${CONVERTED_TOKEN}${prefix}__${newValue.derivative.buckets_path}`;
+    }
+    newObj[`${CONVERTED_TOKEN}${prefix}__${key}`] = newValue;
+    return newObj;
+  }, {});
+}
+
+/**
+ * Building upon the comment for `convertMetricNames`, we are dynamically changing the aggregation names to allow
+ * the single `date_histogram` to work properly. Unfortunately, the code that looks at the response also needs to
+ * understand the naming changes. And yet again, this code is shared amongst the rest of the monitoring code base.
+ * To circumvent this, we need to convert the changed aggregation names back to the original, expected names.
+ * This feels messy, but possible because we keep the original name in the converted aggregation name.
+ *
+ * @param object byDateBucketResponse - The response object from the single `date_histogram` bucket
+ */
+export function uncovertMetricNames(byDateBucketResponse) {
+  const unconverted = {};
+  for (const metricName of LISTING_METRICS_NAMES) {
+    unconverted[metricName] = {
+      buckets: byDateBucketResponse.buckets.map(bucket => {
+        const { key_as_string, key, doc_count, ...rest } = bucket; /* eslint-disable-line camelcase */
+        const metrics = Object.entries(rest).reduce((accum, [key, value]) => {
+          if (key.startsWith(`${CONVERTED_TOKEN}${metricName}`)) {
+            const name = key.split('__')[1];
+            accum[name] = value;
+          }
+          return accum;
+        }, {});
+
+        return {
+          key_as_string, /* eslint-disable-line camelcase */
+          key,
+          doc_count, /* eslint-disable-line camelcase */
+          ...metrics,
+        };
+      })
+    };
+  }
+  return unconverted;
+}