timely-util: avoid rebuilding well-formed bucket chains in restore#36897
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BucketChain::restore allocated a new BTreeMap and moved every bucket on each call, even when the chain was already well-formed. Callers invoke restore after every peel, so this cost ~19% of an MV sink correction buffer prototype's read path. Scan for well-formedness first and return early. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
petrosagg
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…36897) ### Motivation `BucketChain::restore` allocates a fresh `BTreeMap` and moves every bucket over on each call, even when the chain is already well-formed — which is the common case, since callers invoke `restore` after every `peel`. In a correction buffer prototype this churn accounted for ~19% of the read-path samples; the production temporal bucketing operators pay the same cost on every frontier advance. ### Description Scan the buckets for well-formedness (each within two bits of its predecessor, starting from an imaginary -2) and return early without touching the map. The scan is O(buckets) without allocation; the slow path is unchanged. ### Verification Existing `temporal` unit tests pass. Measured ~20% improvement on bucketed correction-buffer benchmarks whose read path peels and restores per timestamp. 🤖 Generated with [Claude Code](https://claude.com/claude-code) Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>
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Motivation
BucketChain::restoreallocates a freshBTreeMapand moves every bucket over on each call, even when the chain is already well-formed — which is the common case, since callers invokerestoreafter everypeel.In a correction buffer prototype this churn accounted for ~19% of the read-path samples; the production temporal bucketing operators pay the same cost on every frontier advance.
Description
Scan the buckets for well-formedness (each within two bits of its predecessor, starting from an imaginary -2) and return early without touching the map.
The scan is O(buckets) without allocation; the slow path is unchanged.
Verification
Existing
temporalunit tests pass.Measured ~20% improvement on bucketed correction-buffer benchmarks whose read path peels and restores per timestamp.
🤖 Generated with Claude Code