Какой частоты рекомендуется использовать для обращения к серверу с целью получения новых сообщений?

The recommended frequency of server requests for new messages depends on the specific application and server load, but generally:

• For real-time chat applications, WebSocket or push notifications are used to receive messages instantly without constant requests.
• If periodic polling is used, the frequency is usually from 5 to 30 seconds.

Frequent polling (e.g., every second) can heavily load the server and network, while infrequent polling may delay receiving new messages.

The optimal approach is to use push technologies (Firebase Cloud Messaging, WebSocket), and if that's not possible, to set up polling with a reasonable interval, such as 10-15 seconds, and increase the interval when there is no activity.