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RedisSMQ / Docs / Queues

Queues

A queue is responsible for holding messages which are produced by producers and are delivered to consumers.

RedisSMQ supports 3 types of queues: LIFO queues, FIFO queues, and Priority queues.

All RedisSMQ queue types are reliable. A queue is said to be reliable, when during a failure scenario, let it be for example a consumer crash, it can recover from such failure and the message being processed is not lost.

In a typical use case, both LIFO and FIFO queues use brpoplpush, which blocks the connection to the Redis server until a message is received. However, priority queues use pooling and lua scripting which introduce a little of overhead on the MQ and therefore priority queues are less performant than other queue types.

In the next examples for simplicity we are going to use a EQueueDeliveryModel.POINT_TO_POINT delivery model for all the queues. But you may choose any combination of EQueueType and EQueueDeliveryModel that fits your application.

LIFO (Last In, First Out) queues

RedisSMQ LIFO Queuing

In a LIFO queue the last published messages are always delivered first and the first published messages are delivered last.

const { Queue, EQueueType, EQueueDeliveryModel } = require('redis-smq');

const queue = new Queue();
queue.save(
  'my_queue',
  EQueueType.LIFO_QUEUE,
  EQueueDeliveryModel.POINT_TO_POINT,
  (err) => {
    if (err) console.error(err);
  },
);

See Queue.save() for more details.

FIFO (First In, First Out) Queues

RedisSMQ FIFO Queuing

In a FIFO queue the first published messages are delivered first and the last published messages are delivered last.

const { Queue, EQueueType, EQueueDeliveryModel } = require('redis-smq');

const queue = new Queue();
queue.save(
  'my_queue',
  EQueueType.FIFO_QUEUE,
  EQueueDeliveryModel.POINT_TO_POINT,
  (err) => {
    if (err) console.error(err);
  },
);

See Queue.save() for more details.

Priority Queues

RedisSMQ Priority Queuing

In a priority queue, messages with higher priority are always delivered first before messages with lower priority.

const { Queue, EQueueType, EQueueDeliveryModel } = require('redis-smq');

const queue = new Queue();
queue.save(
  'my_queue',
  EQueueType.PRIORITY_QUEUE,
  EQueueDeliveryModel.POINT_TO_POINT,
  (err) => {
    if (err) console.error(err);
  },
);

See Queue.save() for more details.

Setting Up a ProducibleMessage Priority

To set up a message priority, the ProducibleMessage Class provides the following methods:

Valid message priority values that you can apply to a given message are:

  • EMessagePriority.LOWEST
  • EMessagePriority.VERY_LOW
  • EMessagePriority.LOW
  • EMessagePriority.NORMAL
  • EMessagePriority.ABOVE_NORMAL
  • EMessagePriority.HIGH
  • EMessagePriority.VERY_HIGH
  • EMessagePriority.HIGHEST

See EMessagePriority.

Queue Namespaces

Queues in RedisSMQ are namespaced.

A queue namespace is used as a scope for a given set of queues to ensure unique queue names and to avoid name collisions when multiple queues share the same name.

A given queue can be either identified by a queue name like orders or explicitly by its queue name and namespace for example { ns: 'my-app', name: 'orders' }.

By default, when a namespace for a queue is not specified, the queue is assigned to the default namespace.

The default namespace can be configured from your configuration object. See Configuration for more details.

Queue Naming Requirements

A queue name is required to fulfill the following requirements:

  • To be composed of alphanumeric characters [a-z0-9] for example queue$ is an invalid queue name;
  • May include - and _ characters for example my-queue or my_queue are valid queue names;
  • To start with an alpha character [a-z] and ends with an alphanumeric character [a-z0-9] for example 3queue or my_queue_ are invalid queue names;
  • Is allowed to include dots (.) for denoting queues hierarchy for example sports.football. See Topic Exchange;

Managing Queues and Namespaces

To manage queues and namespaces RedisSMQ provides:

Queue Messages

To manage queue messages use:

Please note that queue acknowledged messages and dead-lettered messages are not saved by default.

To manage acknowledged and dead-lettered messages you need to enable acknowledged/dead-lettered messages storage from your RedisSMQ Configuration.