Cola

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Cola is a simple distributed, transactional queue gem for Ruby backed by Redis. It uses Redis lists to provide its functionality with minimal additions. Cola supports transactions, retries, deadletter queues and timeouts. This gem is based on https://github.com/taganaka/redis-queue

Install

Run

gem install rb-cola

or add this to your Gemfile

gem 'rb-cola'

Usage

Create a queue, push and pop messages to and from the queue:

q = ::Cola::Queue.new
q.push("message")
message = q.pop
q.commit

See the files under examples folder for more information.

Push

You can push messages onto the queue using push or <<:

queue << message
queue.push(message)
queue.push(another_message, ttl: 30) # this message will expire in 30 seconds

Pop

You can pull the messages from the queue with blocking or non-blocking actions. Blocking actions will wait until a message is available to pop. Non-blocking actions will return nil is no message is available.

Envelope

Each message is stored in an envelope when put on the queue. pop and process return the message itself when called. However, you can use pop_with_envelope to get the entire envelope.

Attribute	Description	Default
message	The message	nil
timestamp	Message timestamp	Timestamp of the push
retries	Number of times the message has been retried	0
last_reason	The reason for the last retry failure	nil
version	Envelope version	0
uuid	Unique ID of the message	Automatically generated
ttl	Time to live	0

Retries

By default, if a pop fails, the message is lost and an exception is raised. This can be changed so Cola retries the message more than once. See options for more info. This is most useful when used with the process function in case an exception is raised within the process block.

Deadletter Queue

In case of multiple failures, the message can be pushed to a deadletter queue for further manual inspection. This is disabled by default.

Message Expiry

When pushing messages onto the queue, you can assign them a Time to Live (ttl). Messages will expire after their ttl is passed and they are not picked up for processing.

Options

When creating a queue, you can use the following options:

Option	Description	Default
redis	Redis instance to use	Using the current redis instance
deadletter	Support deadletter queue	false
queue_name	Set the queue name	Random queue name
timeout	Message timeout	0 (No timeout)
retries	Number of retries	0 (No retries)

Example:

q = ::Cola::Queue.new(timeout: 10, redis: @some_redis_instance)