redis-adapter socket.io CPU issue

[devashishg]

I have been using "@socket.io/redis-adapter", I have got one namespaces created and it has multiple number of rooms, and every room there are 3-5 client connected.

Functioning wise It works well,
but with highly concurrent load environment, redis CPU goes very high.
from redis slow logs i have observed that for each requestId
"publish" "socket.io-request#/#" "{\"uid\":\"dGaEaaa\",\"requestId\":\"vsu1L\",\"type\":0,\"rooms\":[\"room1\"]}"

there are 44 response publish commands out of which 4-5 has valid socket Id,
"publish" "socket.io-response#/#" "{\"requestId\":\"vsu1L\",\"sockets\":['socketId']}"

but rest of them has no socketId.
"publish" "socket.io-response#/#" "{\"requestId\":\"vsu1L\",\"sockets\":[]}"

I did not understand much after reading through the documentations what could be the reason.

Socket server setup looks as follow,

const socketConfig: Partial<ServerOptions> = {
        pingInterval: 25000,
        allowEIO3: true,
 };

this.socketClient = new Server(server, socketConfig);

 this.socketClient.adapter(
    createAdapter(this.pubClient, this.subClient),
 );

Please let me know if someone has any idea what could be the reason here.