[SOM] use aggregation for type counts (#168918)

## Summary

Use an aggregation for type counts in SO management instead of scrolling
through all the documents.

---------

Co-authored-by: kibanamachine <[email protected]>

src/plugins/saved_objects_management/server/lib/get_saved_objects_counts.ts

@@ -0,0 +1,45 @@
+/*
+ * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+ * or more contributor license agreements. Licensed under the Elastic License
+ * 2.0 and the Server Side Public License, v 1; you may not use this file except
+ * in compliance with, at your election, the Elastic License 2.0 or the Server
+ * Side Public License, v 1.
+ */
+
+import { estypes } from '@elastic/elasticsearch';
+import type { SavedObjectsFindOptions } from '@kbn/core-saved-objects-api-server';
+import type { SavedObjectsClientContract } from '@kbn/core/server';
+
+export const getSavedObjectCounts = async ({
+  types,
+  options,
+  client,
+}: {
+  types: string[];
+  options: SavedObjectsFindOptions;
+  client: SavedObjectsClientContract;
+}): Promise<Record<string, number>> => {
+  const body = await client.find<void, { types: estypes.AggregationsStringTermsAggregate }>({
+    ...options,
+    type: types,
+    perPage: 0,
+    aggs: {
+      types: {
+        terms: {
+          field: 'type',
+          size: types.length,
+        },
+      },
+    },
+  });
+
+  const buckets =
+    (body.aggregations?.types?.buckets as estypes.AggregationsStringTermsBucketKeys[]) || [];
+
+  const counts = buckets.reduce((memo, bucket) => {
+    memo[bucket.key] = bucket.doc_count;
+    return memo;
+  }, {} as Record<string, number>);
+
+  return counts;
+};

src/plugins/saved_objects_management/server/lib/index.ts

@@ -9,3 +9,4 @@
 export { toSavedObjectWithMeta } from './to_saved_object_with_meta';
 export { injectMetaAttributes } from './inject_meta_attributes';
 export { findRelationships } from './find_relationships';
+export { getSavedObjectCounts } from './get_saved_objects_counts';

src/plugins/saved_objects_management/server/routes/scroll_count.ts

@@ -10,6 +10,7 @@ import { schema } from '@kbn/config-schema';
 import type { IRouter, SavedObjectsCreatePointInTimeFinderOptions } from '@kbn/core/server';
 import { chain } from 'lodash';
 import type { v1 } from '../../common';
+import { getSavedObjectCounts } from '../lib';
 
 export const registerScrollForCountRoute = (router: IRouter) => {
   router.post(
@@ -44,27 +45,19 @@ export const registerScrollForCountRoute = (router: IRouter) => {
       const client = getClient({ includedHiddenTypes });
       const findOptions: SavedObjectsCreatePointInTimeFinderOptions = {
         type: typesToInclude,
-        perPage: 500,
+        ...(searchString ? { search: `${searchString}*`, searchFields: ['title'] } : {}),
+        ...(references ? { hasReference: references, hasReferenceOperator: 'OR' } : {}),
       };
-      if (searchString) {
-        findOptions.search = `${searchString}*`;
-        findOptions.searchFields = ['title'];
-      }
-      if (references) {
-        findOptions.hasReference = references;
-        findOptions.hasReferenceOperator = 'OR';
-      }
+
+      const rawCounts = await getSavedObjectCounts({
+        types: typesToInclude,
+        client,
+        options: findOptions,
+      });
 
       const counts: Record<string, number> = {};
       for (const type of typesToInclude) {
-        counts[type] = 0;
-      }
-
-      const finder = client.createPointInTimeFinder(findOptions);
-      for await (const { saved_objects: savedObjects } of finder.find()) {
-        for (const { type } of savedObjects) {
-          counts[type]++;
-        }
+        counts[type] = rawCounts[type] ?? 0;
       }
 
       const body: v1.ScrollCountResponseHTTP = counts;

src/plugins/saved_objects_management/tsconfig.json

@@ -28,6 +28,7 @@
     "@kbn/shared-ux-router",
     "@kbn/core-ui-settings-browser-mocks",
     "@kbn/core-ui-settings-browser",
+    "@kbn/core-saved-objects-api-server",
   ],
   "exclude": [
     "target/**/*",