[Synthetics] Stop per-card maintenance-window refetch storm on overview scroll

x-pack/solutions/observability/plugins/synthetics/public/apps/synthetics/hooks/use_fetch_maintenance_windows.test.ts

@@ -0,0 +1,38 @@
+/*
+ * 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; you may not use this file except in compliance with the Elastic License
+ * 2.0.
+ */
+
+import { renderHook } from '@testing-library/react';
+import { useQuery } from '@kbn/react-query';
+import { useFetchMaintenanceWindows } from './use_fetch_maintenance_windows';
+
+jest.mock('@kbn/react-query', () => ({
+  useQuery: jest.fn().mockReturnValue({ data: undefined, isLoading: false }),
+}));
+
+jest.mock('../../../utils/api_service', () => ({
+  apiService: { get: jest.fn() },
+}));
+
+const useQueryMock = useQuery as jest.Mock;
+
+describe('useFetchMaintenanceWindows', () => {
+  afterEach(() => jest.clearAllMocks());
+
+  it('sets staleTime equal to the refetch interval, so a component mount between polls does not trigger its own fetch', () => {
+    // This hook is called per-card from the virtualized overview grid
+    // (`MetricItemIcon` -> `useMonitorMWs`). Without a `staleTime` matching
+    // `refetchInterval`, react-query's default `staleTime: 0` treats every
+    // remount as needing a fresh fetch, so scrolling (which constantly
+    // mounts new cards) fires a fetch per card instead of sharing the one
+    // already-cached result.
+    renderHook(() => useFetchMaintenanceWindows());
+
+    const options = useQueryMock.mock.calls[0][2];
+    expect(options.staleTime).toBe(options.refetchInterval);
+    expect(options.staleTime).toBeGreaterThan(0);
+  });
+});

x-pack/solutions/observability/plugins/synthetics/public/apps/synthetics/hooks/use_fetch_maintenance_windows.ts

@@ -38,6 +38,12 @@ export const useFetchMaintenanceWindows = () => {
       ),
     {
       refetchInterval: REFRESH_INTERVAL_MS,
+      // Without this, cached data is stale immediately (the default) and every
+      // component mount re-fetches on top of the interval polling above. This
+      // hook is called per-card from the virtualized overview grid
+      // (`MetricItemIcon` -> `useMonitorMWs`), so scrolling constantly mounts
+      // fresh subscribers — each one triggering its own request otherwise.
+      staleTime: REFRESH_INTERVAL_MS,
     }
   );
 };