Dynamo Kay Ousterhout Goals Small files Always writeable

Dynamo Kay Ousterhout

Goals • Small files • Always writeable • Low latency – Measured at 99. 9 th percentile

Non-goals • Untrusted nodes • Relational schema. Store e u l a V • Hierarchical namespace y e K

Big (Old? ) Ideas

Replication: Store every object on N nodes N=3

Consistent Hashing A B G Key C F E D

Consistent Hashing H A B G Key C F E D

Consistent Hashing + Virtual Nodes H A B G Key C F E D

Conflict Resolution: Vector Clocks

Basic put() N = 3, W = 2 k: v ([G, 1]) H k: v A B G Coordinator C F E D

get() with Sloppy Quorum N = 3, W = 2, R = 2 k? k: v ([G, 1]) G k: v ([G, 1]) A H B Coordinator C F E D

Takeaway: Tunable! Change N, R, W for desired consistency, availability

Antientropy: Merkle Trees Node A Node B Hash of children Object hashes at leaves

More Ideas • • Hinted handoff Explicit join/leave mechanism (gossip-based) Seed nodes Local notion of failure

Comments

System Scope “…the system needs to have scalable and robust solutions for load balancing, membership and failure detection, failure recovery, replica synchronization, overload handling, state transfer, concurrency and job scheduling, request marshaling, request routing, system monitoring and alarming, and configuration management. ”

Triggers • Client registers to be notified when key changes • Challenging with eventual consistency! • Solution: sloppy triggers

Setting N, R, W • …is annoying! • Can we auto-configure R? • What about W?

Supporting Multiple N, R, W • Different availability/consistency tradeoffs for each object • …without making multiple systems