How to increase performance of redis sub?

Question

How to increase performance of redis sub?

I have code like that

var subscribeNewMessages = require("redis").createClient(config.redis.port, config.redis.host);
subscribeNewMessages.subscribe('new-messages');

io.of('/new-messages').on('connection', function (client) {
        subscribeNewMessages.on("message", function(channel, message) {
            var obj = JSON.parse(message);
            if (client.userId == obj.toUserId || client.guestId == obj.toUserId) {
                client.send(message);
            }
            obj = null;
        });
})

And how can I optimize it? Because this code parses string json for each new messages.

Also when I try to publish to redis chanel I need to JSON.stringify

redis1.publish(channelPrefix, JSON.stringify(clientData));

node.js
redis
socket.io
node-redis

Answer 1

There isn't going to be a way to avoid JSON.parse()/JSON.stringify() as long as you're storing js objects. You could use a different serialization format like msgpack, but you're still calling functions to serialize/unserialize your data (also JSON.parse()/JSON.stringify() are already pretty hard to beat performance-wise in node).

I think the only real performance adjustment you could make with the code you've provided is to only parse the JSON once for all clients instead of for each client. Example:

var subscribeNewMessages = require('redis').createClient(config.redis.port, config.redis.host);
subscribeNewMessages.subscribe('new-messages');

var nsNewMsgs = io.of('/new-messages');
subscribeNewMessages.on('message', function(channel, message) {
  var obj = JSON.parse(message),
      clients = nsNewMsgs.connected,
      ids = Object.keys(clients);
  for (var i = 0, len = ids.length, client; i < len; ++i) {
    client = clients[ids[i]];
    if (client.userId == obj.toUserId || client.guestId == obj.toUserId)
      client.send(message);
  }
});

Depending on your application, you might even be able to avoid the for-loop entirely if you can store the socket.id values in your published messages, then you can simply look up clients[obj.userSockId] and clients[obj.guestSockId] because the connected is keyed on socket.id.