Andy Gross from Basho discussed Riak Core, an open source distributed systems framework extracted from Riak. Riak Core provides abstractions like virtual nodes, preference lists, and event watchers to help developers build distributed applications. It is currently Erlang-only but will support other languages. Riak Core aims to allow developers to outsource complex distributed systems tasks and implement their own distributed systems more easily.

1. Building Distributed
Systems With Riak Core
Andy Gross (@argv0)
VP Engineering
Basho
DevNation SF 2010

2. Riak K/V
• Distributed Key-Value Store
• Based on Amazon’s Dynamo
• HTTP and Binary (Protocol Buffers) APIs
• Data access by {Bucket, Key}
• Javascript Map/Reduce
• Link Walking
• Pluggable Storage (Bitcask, InnoDB, ...)

3. High-Level Dynamo
• Decentralized (no “master” nodes)
• Homogeneous (all nodes can do anything)
• Vector clocks (no reliance on physical time)
• Gossip Protocol (no global state)
• Consistent Hashing for replica placement
(a local calculation for each node)

4. N, R, W Values
• N = number of replicas to store (on
distinct nodes)
• R = number of replica responses needed
for a successful read (specified per-request)
• W = number of replica responses needed
for a successful write (specified per-
request)

8. Harvesting A
Framework
• We noticed that Riak code fell into one of
two categories
• Code specific to K/V storage
• “generic” distributed systems code
• So we split Riak into K/V and Core

9. Distributed
Coordination
• Making many machines act like one
• Division of labor
• Load balancing
• State storage
• Mutual exclusion/locking

10. Riak Core Applications
Your App Riak K/V
Riak Core

11. Riak Core Applications
Your App
Your
App Riak K/V
Riak Core

12. Riak Core Abstractions
• Virtual Nodes
• Preference Lists
• Ring Event Watchers
• Node Event Watchers

13. Virtual Nodes
• Primary actor in a Dynamo-based system
• Handles load for (1/num_partitions)
• Implements commands dispatched from
clients
• Handles handoff when nodes join/leave

14. Preference Lists
• Lists of virtual nodes obtained by hashing a
request (document, sessionid, etc).
• Allows any node to compute document
locations
• Central to replication in Riak
• Down nodes are filtered out, replaced with
next-best nodes in the ring.

15. Ring Event Watchers
• Notified when ring state changes due to
node addition/removal
• API: ring_update(NewRing)
• Can modify ring state in an app-specific
fashion

16. Node Event Watchers
• Nodes run and advertise “services”
• API: service_update(Services)
• Active service list used to generate per-app
preference lists.

17. Use cases
• If distributed systems isn’t your core
business, outsource it!
• Providing a distribution layer on top of
non-distributed systems like:
• Couch, Redis, Memcached
• Implementing your own systems.

18. Current Status and
Roadmap
• Erlang-only now, but not for long (HTTP
and PB APIs coming)
• Some harvesting left to do (versioned
objects, ring/node handler utilities)
• Project templates - skeleton code for
writing Riak Core-based systems.
• Stronger consistency models (with a Paxos/
ZAB-like protocol)

19. Thanks!
• http://wiki.basho.com
• http://github.com/basho
• http://twitter.com/basho/team
• irc://freenode.net/#riak
• Riak SF Meetup (on meetup.com)
• Visit us! 795 Folsom @ 4th (Twitter Bldg.)