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. Redis is distributed under the BSD license and is henceforth unbounded by any licensing constraints as in the case of mongodb.

Use Cases
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 Controller
Helps organize messages scoped by every queue.

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.

NOTE: This datastructure is serialized using msgpack.

Queue Controller
Queues are scoped by project, which is prefixed to the queue name.

Queues ( Redis Sorted Set )
Id: queues_set

The set helps faster existence checks, while the list helps paginated retrieval of queues.

Queue Information (Redis Hash)
This Data structure holds all meta information about a queue.

Scope: 

Claims list ( Redis Set )
contains claim ids active for a queue.

Redis ID: 

Claim info(Redis Hash)
Contains the metadata information for a particular claim.

Catalogue Controller
TBD

Pools Controller
TBD

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. It is also one of the requirements for the graduation of Marconi.

Future Work
1. Support Async connections to the redis database.