Deterministic Parallel and Distributed Programming with Clojure

Quick Intro to deterministic parallelism. Practical examples in Clojure. LVar(s), CRDT(s), Bloom, Derflow and others.

Transcript

1. Deterministic Parallel and Distributed Programming with Clojure Quick Intro Alexey Kachayev, 2014
2. About me • CTO at Attendify.com • Clojure, Erlang, Go, Haskell • Fn.py library author • CPython & Storm contributor
3. Find me •@kachayev •github.com/kachayev •kachayev <$> gmail.com
4. Topic
5. Will talk •Parallel & Distributed •Determinism: why & when •Models and approaches
6. Clojure & Concurrency
7. Atom
8. Agent
9. STM
10. core.async
11. Deterministic
12. Non-Deterministic
13. Why Determinism? • easy to reason about • easy to maintain • less bugs • less bugs that you can’t reproduce on your machine • less data losses (no data losses?) • provable correctness
14. Why Determinism? • you should know why determinism is good if you listen to Clojure conference talks • we will talk about "ordering non-determinism" only (there’re many other reasons however)
15. Parallel & Distributed
16. Parallel • > 1 independent workers (actors?) • loose coordination • great opportunities • … at a high price
17. Distribution • More parallelism (!) • For lower latency • For storage replication • For HA • And more … but more non-determinism factors • Unpredictable latencies • "Random" workers crash
18. Deterministic distributed program? lets think…
19. Use consensus, Luke!
20. Consensus • Non-distributed: locks, semaphores etc • Distributed: 2p-commit, paxos, zab, raft • … but this price is too high in many cases! • … you’re trading availability in most cases
21. Is there any other way?
22. Monotonicity
23. Theory • "Logic and Lattices for Distributed Programming" http://goo.gl/5q7CJF • "CRDTs: Consistency without concurrency control" http://goo.gl/Ouu4sc • "A comprehensive study of Convergent and Commutative Replicated Data Types" http://goo.gl/I1alMi • "A Lattice-Theoretical Approach to Deterministic Parallelism with Shared State" http://goo.gl/cdv1UK
24. Theory • Monotonic logic • Bounded Join Semi-Lattices
25. Practice • mobile application • chat message stream • k-ordered message IDs • "latest viewed message" mark • offline-mode support
26. Practice
27. Practice
28. BTW…. we don’t know global events ordering in practice :(
29. Monotonicity!
30. LVar • Haskell library lvish • Monotonically growing, lattice-based data structures • determinism VS. quasi-determinism • threshold reads • freezing variables
31. LVar
32. CRDT(s)
33. CRDT • Conflict-Free Replicated Data Type • Convergent Replicated Data Type • Commutative Replicated Data Type
34. CRDT: The Idea
35. CRDT • Counters (G-Counter, PN-Counter) • Registers (LWW-Register, MV-Register) • Sets (G-Set, 2P-Set, PN-Set, OR-Set) • Graphs
36. Knockbox
37. Dataflow programming
38. Bloom • disorderly programming • state represented with lattices (few built-in) and collections (table, scratch, channel) • runtime implementation as Ruby DSL • static analysis tools (points of order) • visualisation tools
39. Bloom
40. Derflow • Deterministic dataflow programming • Growing set of single-assignment variables • Operations: declare, bind, read/wait • Streams: produce/consume • Erlang implementation: http://goo.gl/lnnfVd
41. Summary
42. Why Clojure? • strong concurrency primitives (atom) • immutable data types • CRDT library "knockbox" (dead?) • not that much done for distributed computing (riak_core in Erlang) • one can use Akka/Pulsar • aphyr/jepsen for testing partition tolerance • a big room for experiments
43. Links • "Eventually Consistent Data Structures" http://goo.gl/HgtIzY • "Knockbox, an Eventual Consistency Toolkit" http://goo.gl/r5XxRH • "LVars: lattice-based data structures for deterministic parallelism" http:// goo.gl/IJljEQ • "MVar, IVar, and LVar programs in Haskell" http://goo.gl/dF36k4 • "Distributed deterministic dataflow programming for Erlang" http://goo.gl/ y2oH0P • "Sync Free" http://goo.gl/qXZHnb
44. Learn Clojure For Great Good
45. Learn Haskell For Great Good
46. Q/A thanks for your attention,