fix(bench): query the corpus tenant in b2/otel-demo (was always empty)

[jensholdgaard]

What

Fixes a latent bug in the b2/otel-demo bench arm that made it silently measure an empty query, and surfaced it by running the bench against the real frozen otel-demo corpus (the corpus/otel-demo-v* release assets — fetched with gh release download, no container runtime needed).

The bug

b2/otel-demo hardcoded tenant: "a", but the corpus loader writes every record under bench-tenant (corpus.rs BENCH_TENANT). So the query hit the RFC0007.5 empty-result early return and "benchmarked" a 0-row query at ~1.1 µs — a meaningless number the arm had always produced (it's env-gated, so it had never been validated against a real corpus). The b2/synthetic arm was unaffected (it writes its own records under "a").

Fix

• BuiltStore now carries the tenant it wrote under (&'static str; the loader is single-tenant).
• template_exact takes a tenant; b2/otel-demo uses built.tenant and probes the query up front, asserting it returns busiest_template_rows — so a future tenant/template mismatch fails loudly instead of silently timing an empty query. The probe also logs scanned/pruned row groups + bytes.

Validated against the real corpus (indicative, laptop — NOT §9)

corpus	mined rows	files	busiest template → result	row groups scanned	latency
v1	38,782	1	t29 → 4,682	1/1	783 µs
v4	735,377	5	t45 → 89,382	5/5	2.9 ms

Headline finding (the synthetic bench hid it): on real data a template-exact query prunes nothing (v4 scanned 5/5 row groups) — a template recurs in every time partition, so every row group's template_id min/max matches. b2/synthetic isolated each template to its own file, which made pruning look perfect; real logs don't. The inverted-index-collapse locality needs the time-range predicate + partition pruning (the querier's explicitly-deferred refinement). Captured in scratch/b2-otel-demo-findings.md; this shapes the real B2 measurement (a time-windowed query) and is a strong argument for prioritizing partition-level time pruning.

Tests

• store.rs rejects_a_non_empty_bucket still green; BuiltStore.tenant populated from the loader constant.
• The otel-demo probe assertion is the regression guard (empty-query result now fails the bench).
• Local: cargo fmt --all --check, cargo clippy --workspace --all-targets --all-features -D warnings, cargo test --workspace all green.

Part of epic #81. Follow-up: a CI workflow that fetches the frozen corpus and runs b1/b2 (the b1/otel-demo arm wiring + partition-time-pruning are separate).

🤖 Generated with Claude Code

[jensholdgaard]

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ℹ️ Review info

⚙️ Run configuration

Configuration used: defaults

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Run ID: 10b13115-a917-4c77-b712-8fd0fb3d8539

📥 Commits

Reviewing files that changed from the base of the PR and between 166662b and 3957022.

📒 Files selected for processing (2)

• crates/ourios-bench/benches/b2.rs
• crates/ourios-bench/src/store.rs

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix/b2-otel-demo-tenant

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[Copilot]

Pull request overview

This PR fixes the b2/otel-demo Criterion bench arm so it queries the same tenant that the corpus loader writes under, preventing silent “0-row” measurements and adding an up-front probe that fails loudly if the bench is miswired.

Changes:

• Extend BuiltStore to carry the tenant used during corpus load/write, and populate it from corpus::BENCH_TENANT.
• Update the b2 bench helper to build QueryRequests with an explicit tenant, and wire b2/otel-demo to use built.tenant.
• Add an otel-demo probe assertion plus additional logging of query scan/prune stats to surface empty/incorrect queries immediately.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
crates/ourios-bench/src/store.rs	Adds BuiltStore.tenant and returns the loader’s BENCH_TENANT so downstream benches can query the correct tenant.
crates/ourios-bench/benches/b2.rs	Threads tenant into template_exact, uses built.tenant for otel-demo, and probes/logs query results and scan stats before benchmarking.

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