Implement a Simple FIFO Queue

Problem

You want to use Redis to implement a simple abstract first-in, first-out queue, with basic push and pop operations.

Solution

Redis' built-in List datatype is a natural-born queue. To effectively implement a simple queue, all you need to do is utilize a limited set of List operations.

redis> LPUSH queue1 tom
(integer) 1
redis> LPUSH queue1 dick
(integer) 2
redis> LPUSH queue1 harry
(integer) 3
redis> RPOP queue1
tom
redis> RPOP queue1
dick
redis> RPOP queue1
harry

Discussion

Redis comes with four basic list push and pop operations (RPUSH, LPUSH, LPOP, RPOP), as well as blocking pop operations. They are all O(1) operations, so the time complexity of the commands does not depend upon the length of the list.

Implementing a simple queue atop the Redis commands is straight-forward and is a good introduction to building thin Redis-powered abstractions.

For example, here's a Python queue that provides object-level interaction (and uses INCR to ensure a unique ID for each new queue):

r = redis.Redis()

class Queue(object):
    """An abstract FIFO queue"""
    def __init__(self):
        local_id = r.incr("queue_space")
        id_name = "queue:%s" %(local_id)
        self.id_name = id_name

def push(self, element):
    """Push an element to the tail of the queue""" 
        id_name = self.id_name
        push_element = redis.lpush(id_name, element)

def pop(self):
    """Pop an element from the head of the queue"""
        id_name = self.id_name
        popped_element = redis.rpop(id_name)
        return popped_element

See Also