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Idempotent Transactional Workflow (POPL 2013)

Idempotent Transactional Workflow (POPL 2013). G. Ramalingam Kapil Vaswani Microsoft Research India. The Problem. Can we simplify writing such applications?. Application. Partitioned Data. s cale-out. Transfer ( amt , acct1, acct2) { Debit amt from acct1; Credit amt to acct2; }.

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Idempotent Transactional Workflow (POPL 2013)

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  1. Idempotent Transactional Workflow(POPL 2013) G. Ramalingam Kapil Vaswani Microsoft Research India

  2. The Problem Can we simplify writing such applications? Application Partitioned Data scale-out

  3. Transfer (amt, acct1, acct2) { • Debit amt from acct1; • Credit amt to acct2; • }

  4. ACID Transaction • Strong consistency • Distributed transaction • Transfer (amt, acct1, acct2) • atomic { • Debit amt from acct1; • Credit amt to acct2; • }

  5. Workflow • Weaker consistency • No isolation • No distributed transaction • Transfer (amt, acct1, acct2) • atomic {Debit …}; • atomic {Credit …}; Claim: Workflows are common in applications over partitioned data What about process failure?

  6. The Problem Modern Cloud Platforms • Goal • Fault-tolerance in application • A transactional workflow engine • decentralized! Application Logic Stopping (non-byzantine) failure Storage Layer (failures handled by storage layer)

  7. Making Workflows Fault-Tolerant request response

  8. Taking a step back … Request or response may be lost! Resending messages is a critical element of fault-tolerance • Transfer (amt, acct1, acct2) { • Debit amt from acct1; • Credit amt to acct2; • } Must be Idempotent! (tolerate duplicate messages)

  9. Goal:IdempotentFault-Tolerance • (Idempotent Workflow) • A program is said to be idempotent & fault-tolerantiff • its behavior is unaffected by process failures • its behavior is unaffected by duplicate input requests • Behavioral equivalence: • duplicate output responses allowed • progress (liveness) conditions • slightly weakened

  10. Making WorkflowsIdempotent & Fault-Tolerant request response

  11. Making Computations Idempotent request response Make every effectful step idempotent: Associate unique id with every step Modify step to log execution of step Modify step to check if it has already executed All must be done atomically !

  12. AutomatedIdempotent Fault-Tolerance • As a library • In C# & F# • Technically, a monad • As a compiler • As a programming-language construct

  13. Formal Results Theorem. A well-typed monadic program is idempotent and fault-tolerant. Any (well-typed) program e can be automatically translated (compiled) into a program compile[e] Theorem. compile[e] is an idempotent and fault-tolerant realization of e.

  14. Idempotence: A Language Construct • “idworkflowuid e’’ • transfer (uid, amt, acct1, acct2) { • idworkflowuid{ • atomic T1 Debit amt from acct1 • atomic T2 Credit amt to acct2} • } • }

  15. Extensions • Compensating actions • Undo earlier actions when later actions encounter logical failure • Automatic retry • Detect process failures & restart • Checkpointing • Restart at most recent checkpoint

  16. Questions? Fault-Tolerance & Idempotence: Simpler Together

  17. Problem Setting client service Application Logic Storage Layer partitioned data

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