Plan: borrowed-view types for zero-allocation percentile queries#16
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thinkingfish merged 4 commits intomainfrom Apr 30, 2026
Merged
Plan: borrowed-view types for zero-allocation percentile queries#16thinkingfish merged 4 commits intomainfrom
thinkingfish merged 4 commits intomainfrom
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Design notes for adding CumulativeROHistogram*Ref and SparseHistogram*Ref view types that let columnar consumers compute quantiles directly off &[u32] slices without per-snapshot allocation or revalidation. https://claude.ai/code/session_01KZce8ZFiJEunLpALcsqxES
Refactor CumulativeIter/QuantileRangeIter/SparseIter structs to hold &[u32] slices directly instead of a reference to the owned histogram, enabling both owned and ref types to return the same iterator type. Add four borrowed-view types generated via the existing macros: - CumulativeROHistogramRef<'a> / CumulativeROHistogram32Ref<'a> - SparseHistogramRef<'a> / SparseHistogram32Ref<'a> Each ref type is Copy and mirrors the read-only API of its owned counterpart (from_parts, from_parts_unchecked, config/index/count accessors, iter, quantiles/quantile, SampleQuantiles trait impl, From<&Owned>, IntoIterator). Cumulative refs additionally expose iter_with_quantiles, bucket_quantile_range, and total_count. Validation logic is DRYed: owned from_parts delegates to the ref type's private validate() fn. Owned quantile methods delegate via as_ref(). New tests cover validation parity, quantile parity, unchecked constructor, From<&Owned>, iterator agreement, bucket_quantile_range, empty/single-sample edge cases, and u32/u64 symmetry (~30 new tests across both files).
Bump version to 1.3.1-alpha.0 (feature PR off main@1.3.0) and add [Unreleased] CHANGELOG entries for the four new ref types, from_parts_unchecked, as_ref(), From<&Owned>, and SampleQuantiles impls. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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Summary
Design notes only — no implementation yet. Captures the plan for adding
CumulativeROHistogram*Ref<'a>andSparseHistogram*Ref<'a>borrowed-view types that let columnar consumers (e.g. metriken-query) compute quantiles directly off&[u32]slices without per-snapshotVecallocation or revalidation.For a 1k-snapshot × 4-percentile query this drops ~2k transient allocations.
See
IMPLEMENTATION_PLAN.mdfor the full design:Copy, slice-borrowing, lifetime)from_parts+ hot-pathfrom_parts_uncheckedas_ref()/From<&Owned>/IntoIterator/SampleQuantilesimplscumulative.rsandsparse.rslib.rsre-exports1.3.1-alpha.0Test plan
cargo testpasses (including new validation/parity/iterator/edge-case tests)cargo clippy --all-targets --all-features -- -D warningscleancargo doc --no-depsrenders new typeshttps://claude.ai/code/session_01KZce8ZFiJEunLpALcsqxES
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