docs(rfc): RFC 0005 §3.6 amendment — blooms on trace-context ids, with measured evidence

[jensholdgaard]

What

The RFC 0005 §3.6 amendment recording #489's bloom filters on trace_id/span_id — the evidence-first sequencing agreed with the maintainer: code + pre-merge measurement first (runs #12/#14), the RFC text now carrying the measured numbers.

The amendment also corrects the original table's reasoning on the record: "dict and bloom both lose" conflated two different costs. Dictionaries lose on near-random ids (true); the bloom is the only pruning mechanism an exact-id lookup has, precisely because those same ids defeat min/max statistics. Measured cost of the original decision: 72.4 MB to find 9 rows (run #12); with blooms: 4.8 MB (run #14) and the RFC 0031 L3 must-win passes at 21.9× / 514.6×.

Invariants / hazards

Docs-only. §3.5 unaffected (blooms are optional column metadata; both compat directions unaffected, stated in the amendment).

Checks run

mdbook build (clean), cargo fmt --all --check (trivially — no code).

🤖 Generated with Claude Code

https://claude.ai/code/session_01WQY9wfrfRggqSpMLH8Xj3Y

Summary by CodeRabbit

• Documentation
  • Updated the Parquet storage guidance to specify bloom-filter support for trace and span identifiers.
  • Documented measured improvements in data pruning and query performance.
  • Clarified that the change affects metadata only and remains compatible with existing files and readers.

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Review details

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: c7b572a2-4d52-4eb7-b724-b12d97b21fc5

📥 Commits

Reviewing files that changed from the base of the PR and between bc2612c and 3245306.

📒 Files selected for processing (1)

• docs/rfcs/0005-parquet-storage.md

📝 Walkthrough

Walkthrough

The Parquet storage RFC now enables bloom filters for trace_id and span_id while retaining disabled dictionary encoding, and documents the rationale, measured query effects, and metadata-only compatibility behavior.

Changes

Parquet encoding policy

Layer / File(s)	Summary
Trace-context bloom-filter policy docs/rfcs/0005-parquet-storage.md	The encoding table enables bloom filters for trace_id and span_id, and a dated amendment documents the rationale, measurements, and compatibility details.

Estimated code review effort: 1 (Trivial) | ~3 minutes

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly states the RFC amendment and the bloom-filter change for trace-context IDs.
Description check	✅ Passed	The PR description covers the change, rationale, hazards, and checks, but it omits the template's Related and Checklist sections.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch rfc0005-bloom-amendment

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[Copilot]

Pull request overview

Updates RFC 0005’s Parquet encoding policy rationale to reflect measured evidence that bloom filters materially improve exact trace_id/span_id lookups, and records the benchmarking results that motivated the change.

Changes:

• Mark trace_id and span_id as bloom-filtered in the §3.6 encoding policy table.
• Add a dated amendment block explaining why blooms help near-random IDs and citing comparative run measurements.

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[coderabbitai]

Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@docs/rfcs/0005-parquet-storage.md`:
- Around line 556-571: The amendment’s bloom-filter reduction figure is
arithmetically inconsistent: 72.4 MB divided by 4.8 MB rounds to 15.1×. Update
the “With blooms (run `#14`)” sentence to say 15.1×, unless authoritative
unrounded measurements are available and should be cited instead.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

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ℹ️ Review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: 0000f871-140f-4005-ab62-1080f55c6d7d

📥 Commits

Reviewing files that changed from the base of the PR and between 44296d2 and bc2612c.

📒 Files selected for processing (1)

• docs/rfcs/0005-parquet-storage.md

[Copilot]

Pull request overview

Copilot reviewed 1 out of 1 changed files in this pull request and generated 1 comment.

[Copilot]

Pull request overview

Copilot reviewed 1 out of 1 changed files in this pull request and generated 1 comment.

[Copilot]

Pull request overview

Copilot reviewed 1 out of 1 changed files in this pull request and generated no new comments.