Redis Storage Driver Design (Zaqar)

Objective

Redis is an in memory key-value datastore which can organize data as strings, hashes, lists, sets, sorted sets, bitmaps and hyperloglogs. Being In-memory makes it in ideal candidate for high load, low latency messages.

The main use cases of the driver are listed below:

1. High-throughput (2K+ messages/sec per queue)

2. Lots of small messages (<= 1K)

3. Messages are short-lived (minutes, not hours)

4. High durability is optional (2 copies, RAM only)

5. HA is still very important

Components of the basic driver

The basic driver includes support for a single instance redis store as a data backend.

The driver supports 6 main required functions of a marconi storage driver which are:

Message Controllers

Helps organize messages scoped by every queue.

Organization of Data

Message id's list ( Redis Sorted Set )
Each queue in the system has a set of message ids currently in the queue. The list is sorted based on a ranking which is incremented atomically using the counter(MESSAGE_RANK_COUNTER_SUFFIX) also stored in the database for every queue.

Messages(Redis Hash): Each message is stored using the UUID of the message as the redis key. The datastructure has the following information.

Name	Field
id	id
created iso	cr_iso
ttl	t
expires	e
body	b
claim	c
claim expiry time	c.e
client uuid	u
created time	cr

2. Queue Controller 3. Claims Controller 4. Catalogue Controller 5. Pools Controller

Current Status

The basic driver is a "Work in Progress" and is expected to be a part of the code base by Juno-3 deadline (Sept 4th 2014). The clustering and persistence extension is expected to be developed before the end of Kilo.

Blueprints

Blueprint URL	Functionality
[1]	Redis as an alternative driver for MongoDB
[2]	Redis Storage Driver for Marconi

Submitted Patches

Patch URL	Implemented Feature
[3]	Messages and Queue Controllers
[4]	Claims Controller
[5]	Pools and Catalog Controllers