Node & Redis: Redis Clients

Question

Assume you have multiple db's in Redis you would like to insert and/or remove data from. You have a flow like;

• Insert data to DB #1
• After the first insertion's callback do some stuff and insert data to DB #2
• After the second insertion's callback do some stuff again and finally insert data to DB #3

I use one variable called redisClient that is basically created as;

redisClient = redis.createClient();

And while selecting a new DB, I use select command with the extra pre-caution callback, so my select command is like;

redisClient.select(1, function(err) {
  //Some programming logic (Insertion, deletion and stuff)
  redisClient.select(2, function(err) {
    //Do some additional programming logic (Insertion, deletion and stuff)
  }
});

However things get constantly mix. I would like to note that the redisClient variable has been assigned only once and later on used throughout the entire application. Now I was wondering, how reasonable would it be to use seperate redisClients for each DB I have in Redis. So it would be like;

redisClientForDB1 = redis.createClient();
redisClientForDB2 = redis.createClient();
redisClientForDB3 = redis.createClient();

I was wondering would it be reasonable, or would it be a right way for an application that will receive 4K requests per sec and about to go to the production mode. What issues this model might face?

Answer 1

Just as Carl Zulauf said, it's best to open 3 different connections (one per DB):

redisClient = {
  DB1: redis.createClient(),
  DB2: redis.createClient(),
  DB3: redis.createClient()
};

It's best to open all connections once during the initialization of your server:

async.parallel([
  DB1.select.bind(DB1, 1),
  DB2.select.bind(DB2, 2),
  DB3.select.bind(DB3, 3)
], next);

So, after you created redisClient object and initialized it you can use it to handle all your redis operations.

If you'll use redis this way node will open 3 (and only 3) connections per node process.

---

N.B. It's also a good idea to put it all into one node module:

module.exports = {
  DB1: redis.createClient(),
  DB2: redis.createClient(),
  DB3: redis.createClient(),
  init: function(next) {
    var select = redis.RedisClient.prototype.select;
    require('async').parallel([
      select.bind(this.DB1, 1),
      select.bind(this.DB2, 2),
      select.bind(this.DB3, 3)
    ], next);
  }
};

Then you'll be able to initialize all your redis connections by calling init function once (because node caching require calls):

require('./lib/my_redis').init(function(err) {
  if (err) throw err;
  server.listen();
});

Then when require('./lib/my_redis').DB1.set('key','val') will be called in any of your modules DB1 will be already initialized.