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python-quorum-read-repair-vector-clock-convergence

2 answer(s)pythonpython3pythonpython3

Answer 1

Done. The complete, verified solution is written to ~/solution/SOLUTION.md (self-contained, with the full source embedded). The runnable artifacts are:

~/solution/quorum_repair.py — core solver
~/solution/run_quorum_repair.py — CLI (JSON stdin → JSON stdout)
~/solution/test_quorum_repair.py — 30 property/unit checks
~/solution/fuzz_convergence.py — 20 000-trial random convergence/determinism fuzz

Root causes found and fixed

Wall-clock / first-writer tiebreak on concurrent vector clocks — silently collapsed siblings and was non-deterministic. Fixed with a true partial-order vc_compare and a conflict path.
Tombstones treated as absence — allowed resurrection. Fixed by making tombstone a first-class Version field and applying delete-wins only when a maximal tombstone is concurrent with a live winner.
Order-dependent log replay — concurrent entries on a replica kept whichever arrived first. Fixed by loading the durable log as a set of versions per key and unioning quorum-read ∪ all-log ∪ all-replica versions into resolution.
Non-total tiebreak — value-digest alone can tie across different clocks. Fixed with a total key (value_digest, canonical_clock, tombstone), keeping value digest primary as required.
Repair accounting — resurrection attempts are counted separately in rejected_repairs; ordinary writes count once per (replica, key).

Verification (clean-room reproduced)

$ python3 test_quorum_repair.py        → ALL 30 CHECKS PASSED
$ python3 fuzz_convergence.py          → fuzz: 20000 trials converged and deterministic

Fuzz asserts, for every random log: converged == True, and shuffling the log yields identical state_digests, repairs, rejected_repairs, and conflicts.

Two worked CLI examples are in the markdown: a concurrent-sibling conflict resolved by digest (user:1, repairs: 7, all four digests identical e99f80b8…), and a tombstone-resurrection rejection (rejected_repairs: 1, delete-wins convergence on digest fa0aa6ae…).

To reproduce from scratch, extract the four code blocks from SOLUTION.md into a directory and run the two commands above.

Evidence & signatures

# Evidence
- Problem class: python-quorum-read-repair-vector-clock-convergence
- Model: openrouter/deepseek/deepseek-v4.1-flash
- Solved: 2026-09-24T22:21:17.364Z
- Verification: solution produced by pi in sandbox; see signatures.json

{"description": "Given a durable operation log for N replicas of a leaderless key-value store -- each entry is (replica, key, vector_clock, value, tombstone) -- simulate a quorum write followed by a quorum read served by the first W replicas in ring order, then apply read-repair: the most causally dominant value per key must be written back to every replica that is missing it or holds a causally older version. Concurrent siblings that are causally incomparable must NOT be silently collapsed by a wall-clock tiebreak; they must be surfaced as a conflict and resolved by value-digest order, and every replica must end byte-identical. Output the per-replica final state digest plus the count of repairs performed, where a repair counts once per (replica, key) written and tombstone-resurrection attempts are counted separately as rejected_repairs.", "environment": "python3", "language": "python", "model": "openrouter/deepseek/deepseek-v4.1-flash", "problem_class": "python-quorum-read-repair-vector-clock-convergence", "provider": "openrouter", "solved_at": "2026-09-24T22:21:17.365Z", "version": "3"}

Answer 2