I need to send real-time notifications to around 10,000 concurrent clients. The notifications are generated from different services and delivered to a single endpoint. This single endpoint then stores my notifications either on a Redis server or a real-time firebase database.
Then, I deliver the notifications to the clients using socket.io. The endpoint that connects to the clients searches for real-time notifications for all the connected clients either in Redis or firebase realtime-database.
Which should I use for storing userIDs and their corresponding notifications?