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make CLS play nice with Redis

node-redis is fast. It uses a lot of smart techniques to do this that lean heavily upon Redis's architecture. One of its biggest wins is the way that it takes advantage of pipelining to batch up commands and push them to the Redis server in chunks. This works great, unless you're using CLS, which wants to provide consistent access to stored values across entire asynchronous call chains. You could use ns.bind to put all your Redis callbacks on the correct continuation chain, but that breaks down if you forget even one callback passed to client.get().

This shim's job is to take care of the bookkeeping for you. It monkeypatches the Redis driver to ensure that all the callbacks you provide are bound to the CLS namespace you provide to the shim. Use it like so:

var cls = require('continuation-local-storage');
var ns = cls.createNamespace('test');
var patchRedis = require('cls-redis');
var redis = require('redis');
var client = redis.createClient();

You can patch Redis for more than one namespace, but you're going to notice the performance impact pretty quickly, so try not to do that.

Also, if you're using CLS with Q, you're probably going to want to take a look at cls-q as well. At some point, I may figure out how to eliminate the need for it, but both Q and node-redis like to hide their callbacks in such a way that CLS and the asyncListener infrastructure have a hard time capturing them.


The tests assume a Redis server is up and running on localhost on the standard port.