From 42fbfd7e4dd04794e1820b2ff8a2c860885cba5e Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Alejandro=20Fern=C3=A1ndez=20Haro?=
 <alejandro.haro@elastic.co>
Date: Tue, 17 Aug 2021 21:46:54 +0100
Subject: [PATCH] Add debounce to the status observers to reduce unnecessary
 CPU loops (#108952)

---
 src/core/server/status/plugins_status.test.ts | 31 +++++++++++++++++--
 src/core/server/status/plugins_status.ts      |  1 +
 2 files changed, 30 insertions(+), 2 deletions(-)

diff --git a/src/core/server/status/plugins_status.test.ts b/src/core/server/status/plugins_status.test.ts
index a6579069acbc0..b7c0733de728e 100644
--- a/src/core/server/status/plugins_status.test.ts
+++ b/src/core/server/status/plugins_status.test.ts
@@ -247,7 +247,6 @@ describe('PluginStatusService', () => {
       subscription.unsubscribe();
 
       expect(statusUpdates).toEqual([
-        { a: { level: ServiceStatusLevels.available, summary: 'All dependencies are available' } },
         { a: { level: ServiceStatusLevels.degraded, summary: 'a degraded' } },
         { a: { level: ServiceStatusLevels.unavailable, summary: 'a unavailable' } },
         { a: { level: ServiceStatusLevels.available, summary: 'a available' } },
@@ -274,7 +273,6 @@ describe('PluginStatusService', () => {
       subscription.unsubscribe();
 
       expect(statusUpdates).toEqual([
-        { a: { level: ServiceStatusLevels.available, summary: 'All dependencies are available' } },
         { a: { level: ServiceStatusLevels.degraded, summary: 'a degraded' } },
         { a: { level: ServiceStatusLevels.unavailable, summary: 'a unavailable' } },
         { a: { level: ServiceStatusLevels.available, summary: 'a available' } },
@@ -357,6 +355,35 @@ describe('PluginStatusService', () => {
       }).toThrowError();
     });
 
+    it('debounces plugins custom status registration', async () => {
+      const service = new PluginsStatusService({
+        core$: coreAllAvailable$,
+        pluginDependencies,
+      });
+      const available: ServiceStatus = {
+        level: ServiceStatusLevels.available,
+        summary: 'a available',
+      };
+
+      const statusUpdates: Array<Record<string, ServiceStatus>> = [];
+      const subscription = service
+        .getDependenciesStatus$('b')
+        .subscribe((status) => statusUpdates.push(status));
+
+      const pluginA$ = new BehaviorSubject(available);
+      service.set('a', pluginA$);
+
+      expect(statusUpdates).toStrictEqual([]);
+
+      const delay = (ms: number) => new Promise((resolve) => setTimeout(resolve, ms));
+
+      // Waiting for the debounce timeout should cut a new update
+      await delay(25);
+      subscription.unsubscribe();
+
+      expect(statusUpdates).toStrictEqual([{ a: available }]);
+    });
+
     it('debounces events in quick succession', async () => {
       const service = new PluginsStatusService({
         core$: coreAllAvailable$,
diff --git a/src/core/server/status/plugins_status.ts b/src/core/server/status/plugins_status.ts
index 6a8ef1081e165..7ef3ddb31d978 100644
--- a/src/core/server/status/plugins_status.ts
+++ b/src/core/server/status/plugins_status.ts
@@ -76,6 +76,7 @@ export class PluginsStatusService {
 
   public getDerivedStatus$(plugin: PluginName): Observable<ServiceStatus> {
     return this.update$.pipe(
+      debounceTime(25), // Avoid calling the plugin's custom status logic for every plugin that depends on it.
       switchMap(() => {
         // Only go up the dependency tree if any of this plugin's dependencies have a custom status
         // Helps eliminate memory overhead of creating thousands of Observables unnecessarily.