Limit fetching index patterns (elastic#56603)

Should address elastic#56352.

I did a look up and it seems like only id and title a really used in case that savedObjectsCache is used. So I simply limited that request to fetch only title

src/plugins/data/public/index_patterns/index_patterns/index_patterns.test.ts

@@ -19,7 +19,12 @@
 
 // eslint-disable-next-line max-classes-per-file
 import { IndexPatterns } from './index_patterns';
-import { SavedObjectsClientContract, IUiSettingsClient, HttpSetup } from 'kibana/public';
+import {
+  SavedObjectsClientContract,
+  IUiSettingsClient,
+  HttpSetup,
+  SavedObjectsFindResponsePublic,
+} from 'kibana/public';
 
 jest.mock('./index_pattern', () => {
   class IndexPattern {
@@ -45,9 +50,17 @@ jest.mock('./index_patterns_api_client', () => {
 
 describe('IndexPatterns', () => {
   let indexPatterns: IndexPatterns;
+  let savedObjectsClient: SavedObjectsClientContract;
 
   beforeEach(() => {
-    const savedObjectsClient = {} as SavedObjectsClientContract;
+    savedObjectsClient = {} as SavedObjectsClientContract;
+    savedObjectsClient.find = jest.fn(
+      () =>
+        Promise.resolve({
+          savedObjects: [{ id: 'id', attributes: { title: 'title' } }],
+        }) as Promise<SavedObjectsFindResponsePublic<any>>
+    );
+
     const uiSettings = {} as IUiSettingsClient;
     const http = {} as HttpSetup;
 
@@ -61,4 +74,27 @@ describe('IndexPatterns', () => {
     expect(indexPattern).toBeDefined();
     expect(indexPattern).toBe(await indexPatterns.get(id));
   });
+
+  test('savedObjectCache pre-fetches only title', async () => {
+    expect(await indexPatterns.getIds()).toEqual(['id']);
+    expect(savedObjectsClient.find).toHaveBeenCalledWith({
+      type: 'index-pattern',
+      fields: ['title'],
+      perPage: 10000,
+    });
+  });
+
+  test('caches saved objects', async () => {
+    await indexPatterns.getIds();
+    await indexPatterns.getTitles();
+    await indexPatterns.getFields(['id', 'title']);
+    expect(savedObjectsClient.find).toHaveBeenCalledTimes(1);
+  });
+
+  test('can refresh the saved objects caches', async () => {
+    await indexPatterns.getIds();
+    await indexPatterns.getTitles(true);
+    await indexPatterns.getFields(['id', 'title'], true);
+    expect(savedObjectsClient.find).toHaveBeenCalledTimes(3);
+  });
 });

src/plugins/data/public/index_patterns/index_patterns/index_patterns.ts

@@ -30,6 +30,8 @@ import { IndexPatternsApiClient, GetFieldsOptions } from './index_patterns_api_c
 
 const indexPatternCache = createIndexPatternCache();
 
+type IndexPatternCachedFieldType = 'id' | 'title';
+
 export class IndexPatterns {
   private config: IUiSettingsClient;
   private savedObjectsClient: SavedObjectsClientContract;
@@ -50,7 +52,7 @@ export class IndexPatterns {
     this.savedObjectsCache = (
       await this.savedObjectsClient.find({
         type: 'index-pattern',
-        fields: [],
+        fields: ['title'],
         perPage: 10000,
       })
     ).savedObjects;
@@ -76,16 +78,18 @@ export class IndexPatterns {
     return this.savedObjectsCache.map(obj => obj?.attributes?.title);
   };
 
-  getFields = async (fields: string[], refresh: boolean = false) => {
+  getFields = async (fields: IndexPatternCachedFieldType[], refresh: boolean = false) => {
     if (!this.savedObjectsCache || refresh) {
       await this.refreshSavedObjectsCache();
     }
     if (!this.savedObjectsCache) {
       return [];
     }
     return this.savedObjectsCache.map((obj: Record<string, any>) => {
-      const result: Record<string, any> = {};
-      fields.forEach((f: string) => (result[f] = obj[f] || obj?.attributes?.[f]));
+      const result: Partial<Record<IndexPatternCachedFieldType, string>> = {};
+      fields.forEach(
+        (f: IndexPatternCachedFieldType) => (result[f] = obj[f] || obj?.attributes?.[f])
+      );
       return result;
     });
   };