feat(engine): Phase 3b-2-b — per-segment timeline dispatch for combinable stats - #48
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…able stats Task #34 gap #1 of 3. The §7 schema-timeline primitive (`SchemaRegistry::timeline_for_metric`) and the cross-schema combiner (`engines::timeline_dispatch::combine_statistic`) landed in PRs #20 / #22 / #25, but `SimpleEngine::handle_query_promql` was still resolving a single `agg_id` via `resolve_agg_info_promql` and running the full query against it. A query whose time range spans a reconfigure boundary (old `agg_id` retired, new `agg_id` created) saw a data cliff for the pre-boundary slice. This PR wires the dispatcher: * New `SimpleEngine::try_handle_query_promql_via_timeline`: 1. Parse + pattern-match the query, extract metric name. 2. Build a probe `QueryExecutionContext` to read the resolved `[t1, t2]` + `Statistic`. 3. Call `timeline_for_query(metric, t1, t2)`. Bail out with `None` (fall-through to default single-agg path) if fewer than two segments, or if the statistic is non-combinable (quantile / topk / cardinality / rate / increase — those follow in PR B2 with a Partial HTTP response surface). 4. Per segment: reuse `build_query_execution_context_promql_for_agg_id` from PR #37 (the extracted forced-agg-id entry point), clip the store plan's `[start, end]` to the segment's bounds, execute, collect results. 5. Group by label-tuple and fold per-group per-segment scalars through `combine_statistic`. Emit the combined scalar as an `InstantVectorElement`. Purged segments or segments whose `agg_id` is no longer in the config go into `unresolved` so the combiner sees them. * `handle_query_promql` now tries the timeline path first; returns immediately on `Some`, falls through to the existing single-agg path on `None`. Zero behavior change when the timeline has 0–1 segments for the query's metric (the common case today). ## Scope Combinable stats only: Count / Sum / Min / Max. Non-combinable stats still take the single-agg path — PR B2 will surface `CombinedResult::Partial` on the HTTP response so users see `{covered, missing: [segments]}` explicitly instead of a silent data cliff. ## Validation - `cargo test -p query_engine_rust --lib` — 728 pass (baseline unchanged; the dispatcher stays dormant when tests only register one schema per metric). - `cargo clippy --all-targets -- -D warnings` — clean - `cargo fmt --all -- --check` — clean ## Follow-ups (explicit non-scope here) - **Integration test** seeding two agg_ids + cross-boundary Sum query. Requires the full `PrecomputeEngine` setup harness the existing e2e tests use; deferred as a dedicated PR so this one stays a focused dispatcher patch. - **PR B2**: Partial response surface for non-combinable stats on the HTTP adapter. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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Task #34 gap #2 of 3. #48's dispatcher activated per-segment execution for combinable stats (Count/Sum/Min/Max) but refused to run for non-combinable stats (Quantile/Topk/Cardinality/ Rate/Increase) — those still fell through to the single-agg path and saw the same data cliff the dispatcher was written to prevent. Reason: there was no way to tell the HTTP caller "this answer is Partial because the query spans a reconfigure boundary and the statistic can't be combined scalarly." Changes: - **`QueryResult::vector_with_warnings` + `warnings()` accessor.** `InstantVector` and `RangeVector` gain a `#[serde(default, skip_serializing_if = "Vec::is_empty")]` `warnings: Vec<String>` field. Default constructors (`QueryResult::vector`, `QueryResult::matrix`) stay wire- compatible — they still serialise without the field when empty, so every existing caller and snapshot test holds. - **Prometheus adapter** adds a top-level `warnings: []` on `PrometheusResponse` (also skip-if-empty), matching upstream's native API. `format_success_response` + `format_range_success_response` thread through any warnings the engine populated; absent → no field. - **Dispatcher** drops the combinable-only early return. The full loop now runs for every statistic whenever the timeline has ≥2 segments. `combine_statistic` still returns `Full(v)` for cleanly-combinable inputs and `Partial { covered, missing }` everywhere else — on Partial we accumulate the `covered` scalar (when present), flag `any_partial`, and build a human-readable warnings list with the metric, range, statistic, dropped-group count, and up to three unresolved segments (agg_id, clipped range, status, coverage). Over-three are summarised; the full set is still inspectable via `GET /api/v1/db/timeline`. 5 new unit tests: 3 in `engines::query_result::tests` covering the default-empty / with-warnings / matrix wire contract; 2 in the Prometheus adapter covering the response-side serialisation contract. 734 lib tests pass (+5), clippy clean, fmt clean. Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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Summary
Task #34 gap #1 of 3 — the blocker for "queries spanning a reconfigure boundary no longer see a data cliff." The §7 schema-timeline primitive (`SchemaRegistry::timeline_for_metric`) and the cross-schema combiner (`engines::timeline_dispatch::combine_statistic`) landed in #20 / #22 / #25, but `SimpleEngine::handle_query_promql` was still resolving a single `agg_id` via `resolve_agg_info_promql` and running the full query against it. A query whose time range spans a reconfigure boundary (old `agg_id` retired, new one created) saw a data cliff for the pre-boundary slice.
This PR wires the dispatcher.
What's in this PR
Scope
Combinable stats only: Count / Sum / Min / Max. Non-combinable stats (quantile / topk / cardinality / rate / increase) stay on the single-agg path — PR B2 will surface `CombinedResult::Partial` on the HTTP adapter so users see `{covered, missing: [segments]}` explicitly instead of a silent cliff.
Zero behavior change when timeline has 0–1 segments for the query's metric (the common case today).
Validation
Follow-ups (explicit non-scope here)
🤖 Generated with Claude Code