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Proposes an AIMD (Additive-Increase / Multiplicative-Decrease) controller that replaces the static CAPACITY_MULTIPLIER and PARALLEL_THRESHOLD knobs with a feedback-driven concurrency limiter. Covers placement, state machine, overload detection, integration points in the engine, transfer, and CLI crates, trade-offs vs Vegas/BBR/Gradient2, implementation phases mapped to tasks #2091-#2093, and open questions on per-pipeline scope, --bwlimit interaction, and local-only feedback signal quality.
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Adds the standalone limiter type defined by the design RFC at docs/design/aimd-concurrency-limiter.md. The implementation lives in crates/engine/src/concurrent_delta/work_queue/limiter.rs and exposes: - LimiterConfig builder with min_limit / max_limit / alpha / beta_num / beta_den / build(). - AimdLimiter with try_acquire, target, in_flight, rtt_ema_nanos, and a pub is_rtt_spike predicate. - RAII Ticket guard (#[must_use]) with record_success / record_overload / record_error and Drop fallback for panic paths. - OverloadReason variants for RttSpike / QueueSaturated / DiskCommitPressure / ErrorRate. Internals follow the RFC: integer-only RTT EMA (alpha_ema = 1/8 per RFC 6298), variance smoothed with beta = 1/4, RTT-spike threshold of ema + 2*sqrt(var) via Newton-method isqrt, slow-start doubling until the first decrease, debounce window of 2*rtt_ema after each multiplicative decrease, and AcqRel/Acquire atomic ordering on every target/in_flight transition. Twelve unit tests cover the algorithm: target saturation (single threaded and under thread contention), additive increase, multiplicative decrease, min/max clamps, debounce suppression, RTT EMA convergence, ticket Drop on panic, transient-vs-deterministic error classification, slow-start doubling, RTT-spike predicate, builder clamps, and the isqrt helper. Not yet integrated. Callers (WorkQueueSender, disk-commit, CLI) are wired in the follow-on tickets: - #2092: convergence tests under injected error. - #2093: --adaptive-concurrency / --no-adaptive-concurrency CLI flag.
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* feat(engine): AIMD concurrency limiter type (#2091) Adds the standalone limiter type defined by the design RFC at docs/design/aimd-concurrency-limiter.md. The implementation lives in crates/engine/src/concurrent_delta/work_queue/limiter.rs and exposes: - LimiterConfig builder with min_limit / max_limit / alpha / beta_num / beta_den / build(). - AimdLimiter with try_acquire, target, in_flight, rtt_ema_nanos, and a pub is_rtt_spike predicate. - RAII Ticket guard (#[must_use]) with record_success / record_overload / record_error and Drop fallback for panic paths. - OverloadReason variants for RttSpike / QueueSaturated / DiskCommitPressure / ErrorRate. Internals follow the RFC: integer-only RTT EMA (alpha_ema = 1/8 per RFC 6298), variance smoothed with beta = 1/4, RTT-spike threshold of ema + 2*sqrt(var) via Newton-method isqrt, slow-start doubling until the first decrease, debounce window of 2*rtt_ema after each multiplicative decrease, and AcqRel/Acquire atomic ordering on every target/in_flight transition. Twelve unit tests cover the algorithm: target saturation (single threaded and under thread contention), additive increase, multiplicative decrease, min/max clamps, debounce suppression, RTT EMA convergence, ticket Drop on panic, transient-vs-deterministic error classification, slow-start doubling, RTT-spike predicate, builder clamps, and the isqrt helper. Not yet integrated. Callers (WorkQueueSender, disk-commit, CLI) are wired in the follow-on tickets: - #2092: convergence tests under injected error. - #2093: --adaptive-concurrency / --no-adaptive-concurrency CLI flag. * style: cargo fmt --all * fix(engine): clippy lints on AIMD limiter (abs_diff, div_ceil, format args)
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…2093) Add convergence tests for the AIMD adaptive-concurrency limiter: - Alternating success/overload stabilizes target within bounded range - Sustained successes grow target monotonically - Debounce window expires after 2 * rtt_ema - Slow-start doubles over multiple windows - Overload during slow-start transitions to additive growth Add --adaptive-concurrency / --no-adaptive-concurrency CLI flag pair, wired through ParsedArgs -> ConfigInputs -> ClientConfigBuilder -> ClientConfig -> WriteConfig. Default is disabled (opt-in).
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…2093) Add convergence tests for the AIMD adaptive-concurrency limiter: - Alternating success/overload stabilizes target within bounded range - Sustained successes grow target monotonically - Debounce window expires after 2 * rtt_ema - Slow-start doubles over multiple windows - Overload during slow-start transitions to additive growth Add --adaptive-concurrency / --no-adaptive-concurrency CLI flag pair, wired through ParsedArgs -> ConfigInputs -> ClientConfigBuilder -> ClientConfig -> WriteConfig. Default is disabled (opt-in).
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…2093) (#3961) Add convergence tests for the AIMD adaptive-concurrency limiter: - Alternating success/overload stabilizes target within bounded range - Sustained successes grow target monotonically - Debounce window expires after 2 * rtt_ema - Slow-start doubles over multiple windows - Overload during slow-start transitions to additive growth Add --adaptive-concurrency / --no-adaptive-concurrency CLI flag pair, wired through ParsedArgs -> ConfigInputs -> ClientConfigBuilder -> ClientConfig -> WriteConfig. Default is disabled (opt-in).
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May 18, 2026
Proposes an AIMD (Additive-Increase / Multiplicative-Decrease) controller that replaces the static CAPACITY_MULTIPLIER and PARALLEL_THRESHOLD knobs with a feedback-driven concurrency limiter. Covers placement, state machine, overload detection, integration points in the engine, transfer, and CLI crates, trade-offs vs Vegas/BBR/Gradient2, implementation phases mapped to tasks #2091-#2093, and open questions on per-pipeline scope, --bwlimit interaction, and local-only feedback signal quality.
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May 18, 2026
* feat(engine): AIMD concurrency limiter type (#2091) Adds the standalone limiter type defined by the design RFC at docs/design/aimd-concurrency-limiter.md. The implementation lives in crates/engine/src/concurrent_delta/work_queue/limiter.rs and exposes: - LimiterConfig builder with min_limit / max_limit / alpha / beta_num / beta_den / build(). - AimdLimiter with try_acquire, target, in_flight, rtt_ema_nanos, and a pub is_rtt_spike predicate. - RAII Ticket guard (#[must_use]) with record_success / record_overload / record_error and Drop fallback for panic paths. - OverloadReason variants for RttSpike / QueueSaturated / DiskCommitPressure / ErrorRate. Internals follow the RFC: integer-only RTT EMA (alpha_ema = 1/8 per RFC 6298), variance smoothed with beta = 1/4, RTT-spike threshold of ema + 2*sqrt(var) via Newton-method isqrt, slow-start doubling until the first decrease, debounce window of 2*rtt_ema after each multiplicative decrease, and AcqRel/Acquire atomic ordering on every target/in_flight transition. Twelve unit tests cover the algorithm: target saturation (single threaded and under thread contention), additive increase, multiplicative decrease, min/max clamps, debounce suppression, RTT EMA convergence, ticket Drop on panic, transient-vs-deterministic error classification, slow-start doubling, RTT-spike predicate, builder clamps, and the isqrt helper. Not yet integrated. Callers (WorkQueueSender, disk-commit, CLI) are wired in the follow-on tickets: - #2092: convergence tests under injected error. - #2093: --adaptive-concurrency / --no-adaptive-concurrency CLI flag. * style: cargo fmt --all * fix(engine): clippy lints on AIMD limiter (abs_diff, div_ceil, format args)
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…2093) (#3961) Add convergence tests for the AIMD adaptive-concurrency limiter: - Alternating success/overload stabilizes target within bounded range - Sustained successes grow target monotonically - Debounce window expires after 2 * rtt_ema - Slow-start doubles over multiple windows - Overload during slow-start transitions to additive growth Add --adaptive-concurrency / --no-adaptive-concurrency CLI flag pair, wired through ParsedArgs -> ConfigInputs -> ClientConfigBuilder -> ClientConfig -> WriteConfig. Default is disabled (opt-in).
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Summary
Testing
Codex Task