fix: high cpu usage with large amount of channels #37395

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Merged

kodiakhq merged 18 commits into develop from fix/SUP-862

Nov 11, 2025

.changeset/quiet-cars-smile.md

-Original file line number
+Diff line change
@@ -0,0 +1,5 @@
+    ---
+    "@rocket.chat/meteor": patch
+    ---
+    Fixes client slowdown for users with large amount of channels

apps/meteor/client/views/root/hooks/loggedIn/useUnread.ts

-Original file line number
+Diff line change
@@ -1,13 +1,15 @@
     import { manageFavicon } from '@rocket.chat/favicon';
     import { useSession, useSessionDispatch, useUserPreference, useUserSubscriptions } from '@rocket.chat/ui-contexts';
-    import { useEffect } from 'react';
+    import { useEffect, useRef } from 'react';
     import { useFireGlobalEvent } from '../../../../hooks/useFireGlobalEvent';
     const query = { open: { $ne: false }, hideUnreadStatus: { $ne: true }, archived: { $ne: true } };
     const options = { fields: { unread: 1, alert: 1, rid: 1, t: 1, name: 1, ls: 1, unreadAlert: 1, fname: 1, prid: 1 } };
     const updateFavicon = manageFavicon();
+    type UnreadData = { unread: number; alert: boolean | undefined; unreadAlert: string | undefined };
     export const useUnread = () => {
     	const unreadAlertEnabled = useUserPreference('unreadAlert');
     	const setUnread = useSessionDispatch('unread');
@@ Expand All / @@ -18,37 +20,48 @@ export const useUnread = () => { @@
     	const subscriptions = useUserSubscriptions(query, options);
+    	// We keep a lightweight snapshot of the last emitted per-subscription unread state so we only
+    	// fire "unread-changed-by-subscription" for subscriptions whose unread-relevant fields changed.
+    	// Previously we emitted one global event per subscription on ANY change, which scaled O(N)
+    	// with the user subscription count (thousands) for every single message event, dominating CPU.
+    	const prevSubsRef = useRef(new Map<string, UnreadData>());
     	useEffect(() => {
-    		let unreadAlert: false | '•' = false;
+    		let badgeIndicator: false | '•' = false;
+    		let unreadCount = 0;
+    		const nextSnapshot = new Map<string, UnreadData>();
-    		const unreadCount = subscriptions.reduce((ret, subscription) => {
-    			fireEventUnreadChangedBySubscription(subscription);
+    		for (const subscription of subscriptions) {
+    			const { rid, unread: unreadValue, alert, unreadAlert: subscriptionUnreadAlert } = subscription;
+    			const prev = prevSubsRef.current.get(rid);
+    			// Emit per-sub event only if something that influences unread UI changed.
+    			if (!prev || prev.unread !== unreadValue || prev.alert !== alert || prev.unreadAlert !== subscriptionUnreadAlert) {
+    				fireEventUnreadChangedBySubscription(subscription);
+    			}
+    			nextSnapshot.set(rid, { unread: unreadValue, alert, unreadAlert: subscriptionUnreadAlert });
-    			if (subscription.alert || subscription.unread > 0) {
-    				// Increment the total unread count.
-    				if (subscription.alert === true && subscription.unreadAlert !== 'nothing') {
-    					if (subscription.unreadAlert === 'all' || unreadAlertEnabled !== false) {
-    						unreadAlert = '•';
+    			if (alert || unreadValue > 0) {
+    				if (alert === true && subscriptionUnreadAlert !== 'nothing') {
+    					if (subscriptionUnreadAlert === 'all' || unreadAlertEnabled !== false) {
+    						badgeIndicator = '•';
     					}
     				}
-    				return ret + subscription.unread;
+    				unreadCount += unreadValue;
     			}
-    			return ret;
-    		}, 0);
+    		}
+    		prevSubsRef.current = nextSnapshot; // swap snapshot
     		if (unreadCount > 0) {
-    			if (unreadCount > 999) {
-    				setUnread('999+');
-    			} else {
-    				setUnread(unreadCount);
-    			}
-    		} else if (unreadAlert !== false) {
-    			setUnread(unreadAlert);
+    			setUnread(unreadCount > 999 ? '999+' : unreadCount);
+    		} else if (badgeIndicator !== false) {
+    			setUnread(badgeIndicator);
     		} else {
     			setUnread('');
     		}
     		fireEventUnreadChanged(unreadCount);
-    	}, [setUnread, unread, subscriptions, unreadAlertEnabled, fireEventUnreadChangedBySubscription, fireEventUnreadChanged]);
+    	}, [setUnread, subscriptions, unreadAlertEnabled, fireEventUnreadChangedBySubscription, fireEventUnreadChanged]);
     	useEffect(() => {
     		updateFavicon(unread);
@@ Expand Down @@

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fix: high cpu usage with large amount of channels #37395

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